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Successional patterns of hard-bottom macrobenthic communities at kelp bed (Lessonia trabeculata) and barren ground sublittoral systems
... Morphological and phylogenetic studies confirmed its presence from Peru along the entire Chilean coast, forming non-continuous populations down to 20-m depth (Villouta and Santelices 1984;Hoffmann and Santelices 1997;Cho et al. 2006;Martin and Zuccarello 2012), and occasionally in intertidal areas when substratum is available (Villouta and Santelices 1986). This stability makes it one of the most important biomass resources in the Southeastern Pacific, sustaining a significant number of understory marine organisms within its forests (Villegas et al. 2008;Uribe et al. 2015;Stotz et al. 2016). It also has been suggested as a pollution bioindicator and putatively as a candidate to clean mining wastewaters, due to its capacity to retain heavy metals for long periods as living or dehydrated material (Sáez et al. 2012;Escudero et al. 2015;Manoli et al. 2015). ...
... Growth rate, prevalence of reproductive individuals and recruitment varied slightly over the sampling period of our study, suggesting that L. trabeculata is part of a mature subtidal community. Our results agree with observations reported by Villouta and Santelices (1984), Vásquez et al. (2006), Uribe et al. (2015) and Stotz et al. (2016). The slow growth may be underestimated by natural blade erosion, which in L. trabeculata from northern Chile may reach up to 0.39 cm day −1 , leading to a loss of about 50% biomass within 1 year (Tala and Edding 2005). ...
... As a compromise, we propose to evaluate pruning of individuals, and some months later to manually remove the thallus leftovers in order to promote recruitment recovery. The impact of these practises must however be analysed in a community context, including consequences on the associated assemblages, which have demonstrated to be highly susceptible to the disruption of this foundational species (Vásquez and Santelices 1990;Uribe et al. 2015). ...
Lessonia trabeculata is one of the most valuable seaweeds in Chile, especially in the northern zone where its harvest has been going on for decades. We carried out population dynamics studies in the Atacama Desert coast (Bahia Chasco), in order to assess its productivity under natural and harvesting scenarios. We found very slow but consistent growth (1.98 cm month⁻¹) and density (3–4 individuals m⁻² with no monthly variation) during 18 months of observations in an undisturbed subpopulation. However, after total harvesting, L. trabeculata exhibited different responses. Its recruitment was season-specific, with exceedingly high values in autumn (ca. 80 individuals m⁻² in 5 months) and a dramatic reduction of recruits in summer (1–5 individuals m⁻² in 7 months, with many areas with no recruitment). Gradually, density values tended to stabilize to growth rates under un-altered conditions. In parallel, pruning systems at three different thallus levels (frond meristem base cuts, removal of half and total canopy) were all inefficient and harmful: (i) Biomass takes longer to be harvested; (ii) pruned individuals die off; and (iii) do not detach easily from the substrata, delaying the recovery by potentially emerging L. trabeculata juveniles. Some of these results agreed with our culture experiments, where 26 months were needed to obtain up to 100 cm long thalli with shrub-like morphology. We conclude that management of L. trabeculata beds must be improved in order to guarantee survival of the industry, and we propose some practices that at some stage should involve the complete removal of older/senescent individuals.
... Ecological succession is defined in general as the perturbation of a specific area leading to changes in the habitat and community, occurring either naturally or by human action (Vaz-Pinto et al., 2014;Uribe et al., 2015;Herbert et al., 2017). Odum (1971) comprehensively summarized the change trends of structural and functional characteristics during ecosystem development, including community energetics, community structure, life history, nutrient cycling, selection pressure, and homeostasis. ...
... The attached community not only provides a food source for organisms at high trophic levels (Lin et al., 2018) but also increases microspatial complexity (Jaubet et al., 2013;Lavender et al., 2017), providing shelter and breeding sites for a variety of swimming organisms (Machado et al., 2019) and allowing them to colonize and grow (Antoniadou et al., 2010;Birdsey et al., 2012). Studies on the succession trend of attached communities in specific sea areas usually use hanging boards of different materials as biological attachment bases, such as PVC boards (Lezzi et al., 2018;Vicente et al., 2021), ceramic boards (Uribe et al., 2015), acrylic boards (Abed et al., 2019), and silicate concrete boards (Zhan et al., 2021). For artificial structures actually deployed in seawater, visual and photographic methods are usually used to identify, record and analyse the attached organisms (Fariñas-Franco and Roberts, 2014;Higgins et al., 2019;Toledo et al., 2020). ...
With the continuous development of ports, ship transportation, resource extraction and artificial habitat deployment, an increasing number of artificial structures have created new usable spaces for marine organisms, and the biological communities living on their surfaces have undergone ecological succession. However, related studies have ignored ecological functions, interspecific relationships, and stability in different successional stages. Based on traditional taxonomy, this study applied functional diversity, niche overlap and niche breadth indexes to compare the attached organisms on artificial reefs (ARs) with different construction times in Bailong Pearl Bay, Fangchenggang City, Guangxi Zhuang Autonomous Region, China. The change trends of richness, habitat resource supply, resource utilization degree and efficiency, and interspecific relationships during the succession process were analysed. The results indicated that richness increased with functional diversity. While the number of species increased, the attached organisms showed different functional characteristics, and the number of species with identical traits decreased. The attached community in the later stage of development had a higher degree of utilization of ecological space, more comprehensive and efficient utilization of effective resources, a stronger degree of complementarity of organismal niches, and weaker interspecific competition. In the early stage of the developmental process, the attached community was affected by more environmental factors and had very significant correlations with those factors. The combination of the niche overlap index and the niche breadth index indicated that the resource supply supporting the survival and development of the attached organisms on the ARs with earlier construction times may be greater. The decrease in the number of biomarkers, the similarity of biomarkers belonging to the same family, and the similarity of dominance alternation all indicated that during the process of long-term development and community succession, the organisms attached to the various parts of the ARs tended to become more similar.
... Consequently, the overexploitation of kelp species could change the natural trajectory of kelp beds, promoting barren grounds in such habitats. Recently, it has been described that both kelp beds and barren grounds show significantly different successional patterns from early stages dominated by micro-periphyton to advanced assemblages shaped by macrobenthic organisms (Uribe et al., 2015a;Uribe et al., 2015b). ...
... Early studies have shown not only that community succession in kelp forests and barrens is habitat and community specific (Uribe et al., 2015a;Uribe et al., 2015b) but also that barren beds exhibit a shorter structural discrete-stage pathway than kelp forests (Uribe & Ortiz submitted). Therefore, the current findings emphasize the relevance of controlling the indiscriminate harvesting of kelp species, since vast coastal areas have become dominated by barrens along the northern Chilean coast (Ortiz & Levins, 2017), modifying the morphology of the remaining plants and reducing the biodiversity (Byrnes et al., 2006;Vega, 2016;Teagle et al., 2017;Miller et al., 2018). ...
Ecological stability based on statistical variability was contrasted with the asymptotical local stability of transient states during successional changes in community structure in kelp forests and barren grounds.
Simplified semi‐quantitative ecological models with different levels of complexity were constructed to represent transient successional states in kelp and barrens, and Routh–Hurwitz's criteria and Levins' criterion of local stability were also estimated.
The results suggest that ecological stability based on statistical variation does not match local (mathematical) stability, since although successional changes in kelp exhibited less variability (measured as percentage coefficient of variation), barren beds were more locally stable. The local stability criteria used in the current work could be a suitable technique for evaluating the likelihood of transient ecological states to resist or change, since it considers states at equilibrium to maintain their properties only against small disturbances.
These outcomes are relevant because the natural alternation between kelp and barrens could be disrupted by the intensive harvest of kelp species carried out over the last 10 years on the central‐north Chilean coast and in other temperate ecosystems.
Additionally, the negative effects of harvesting kelp species could have a synergetic relationship with other drivers such as climate change and coastal pollution. Thus, strict policy managements to limit the kelp harvest are deeply encouraged. A monitoring programme for assessing the current conditions of benthic–pelagic ecosystems along the Chilean coast is also required.
... One of the main studies carried out after installing an artificial reef is into the process of ecological succession by benthic organisms that colonise the structure (González-Duarte et al. 2018, Herbert et al. 2017, Navarro-Barranco et al. 2015, Sen et al. 2014, Uribe et al. 2015, Perkol-Finkel & Benayahu 2005. Several studies suggest that during ecological succession in marine environments on this type of structure, the stages of succession can be identified based on the pattern of development of the communities that settle on the surface (Balqadi et al. 2018, Liu et al. 2017, Vergara et al. 2016, Lozano-Cortés & Zapata 2014, Salta et al. 2013, Sweet et al. 2011, Keough 1998. ...
... Ecological succession is defined in general as the perturbation of a specific area leading to changes in habitat and community, occurring either naturally or by human action (Herbert et al. 2017, Uribe et al. 2015, Vas-Pinto 2014. Several studies suggest that different stages can be identified in the process based on the development of communities settling on the surface (Balqadi et al. 2018, Liu et al. 2017, Vergara et al. 2016, Lozano-Cortés & Zapata 2014, Salta et al. 2013, Sweet et al. 2011, Keough 1998. ...
As part of efforts to restore fishery resources and recover damaged coastal ecosystems, artificial reefs are often anchored on the seafloor in coastal zones, to provide new habitats for marine organisms. The aim of the study was to describe the structure of a community of benthic invertebrates colonising a niche-type artificial reef (AATN in Spanish). Nine structures were anchored at depths of 16 ± 1.5 m for 99 weeks (22 months) in the Area of Benthic Resource Management and Exploitation (AMERB) in coastal waters of the Region of Bio Bio, Chile.
The results showed that, at 3 months from submersion of the NTAR, much of the artificial substrate remained bare and there were only low levels of specimens of Balanus sp. barnacles, showing mean coverage of 11.26%, and even lower proportions of Rhodophyta, with mean coverage of 0.34%. At 6 months, the presence of hydrozoans was seen, decreasing the coverage of the barnacles, which was aided further at 8 months with the arrival of barnacle predatory invertebrates. At 8 months, new benthic invertebrates appeared and competed for the substrate. These included sponges and algae. At 99 weeks, the hydrozoans dominated the substrate, followed by barnacles and Rhodophyta, the first colonising organisms, leading to colonisation by motile macro-invertebrates, mainly consisting of crustaceans, echinoderms and molluscs.
The AATN artificial system provides an ideal substrate for the development of early ecological succession and the use of this technology should be feasible in the recovery process of habitat damaged by anthropogenic actions and climate change.
... This phenomenon, called "getnoguem" in Korea, is similar to "isoyake" in Japan (Fujita, 2010;Lee et al., 2022). Barren grounds are characterized by large areas of bare rock, extensively covered by CCA, and exhibiting low biodiversity (Serisawa et al., 2004;Kang, 2010;Uribe et al., 2015). Around Jeju Island, barren ground coverage has increased by nearly 11% over a 5-year period between 1998 and 2003, at which point it was covering 4541 hectares of coastal seafloor (Kim, 2006). ...
Aim of study
Marine climatic transition zones are boundary areas of major climate zones, here the boundary between the subtropical and temperate zones. They present areas containing high abundance of organisms living at the limit of their physiological tolerance. These marginal populations are particularly sensitive to changes in their environment. As such, marine climatic transition zones are excellent natural playgrounds for climate change-related hypothesis testing, especially with respect to marine habitat response to ocean warming. The marginal biogenic habitats around Jeju Island, South Korea, which lies within the temperate transition zone, have gradually changed from macroalgal-dominated to hard coral-dominated habitats. Understanding the specific abiotic environmental factors that influence the distribution of the marginal populations in temperate transition zones (i.e., species at their occurrence limit) is crucial to predicting and managing temperate zone habitat changes caused by climate change. This study aims to identify the specific abiotic environmental factors that contribute to explaining the current spatial distribution of the declining temperate and expanding subtropical foundation species in Jeju waters.
Methods
Coverage and composition of sessile benthic communities were determined by photo-quadrat analysis at two depths (10 m and 15 m) at three sites along the island’s south, east, and north coasts in May and November 2022. Divergences in community composition between sites were characterized in light of ten quantitative environmental parameters.
Results
Our results show that sessile foundation communities vary significantly at different sites around the island. While the south is defined by high-latitude hard corals, predominately Alveopora japonica, the east is defined by the temperate canopy-forming macroalga Ecklonia cava, and the north is characterized by coralline algae. Winter sea surface temperature, water transparency, nutrient concentration, and water movement were statistically the most impactful environmental factors determining which foundation species constitute each distinct benthic community.
Conclusion
This study provides valuable baseline information on the impacts of abiotic environmental factors on marine sessile communities in a temperate transition zone.
... The coast of Chile is a highly productive system that belongs to the Humboldt Current ecosystem (HCE) Gutiérrez et al., 2016). The subtidal rocky bottoms are frequently dominated by the kelp species, such as Macrocystis pyrifera, Lessonia trabeculata, and Lessonia berteroana (Laminariales; Phaeophyceae) (Stotz et al., 2016), which support conspicuous assemblages conformed for different species of invertebrates, fishes, and other algae (Steneck et al., 2002;Almanza et al., 2012;Uribe et al., 2015;Miller et al., 2018;Riquelme-Pérez et al., (www.ine.cl), developing a variety of interventions, such as those related to the mining industry (loading of mineral concentrates of Cu, Zn, Pb, and Mg), port operations, desalination plants, artisanal fisheries, artificial touristic beaches, and sewage discharge, among others Contreras, 2019). ...
... Communities of invertebrates within Lessonia forests can differ from those in other habitats close to Lessonia forests (Villegas et al. 2008;Vásquez et al 2012;Bularz et al. 2022). For example, ceramic plates placed for 14 months beneath L. trabeculata had a higher number of taxa and density of organisms compared to plates placed in a nearby barren habitat (Uribe et al. 2015). Similarly, following the removal of the canopy of L. trabeculata in Chile, macroinvertebrate diversity declined although fish and sessile understory diversity did not (Bularz et al. 2022). ...
Lessonia (order Laminariales) is a kelp genus restricted to the temperate southern hemisphere, where species form dense forests from the low intertidal to 25 m depth at wave exposed sites. Lessonia spp. are among the most harvested kelps globally due to their importance in providing raw materials for food, cosmetics, bioactive and biomedical industries. Over-harvesting of natural beds can negatively affect Lessonia populations and the many species that depend on these habitats, including commercially important fish and molluscs, but good harvest management plans reduce these impacts on natural Lessonia stocks. However, the increasing demand for raw materials will likely only be met by aquaculture for which Lessonia shows high potential in pilot scale studies undertaken in Chile, New Zealand, and Australia. In this concise review, we highlight the current knowledge of Lessonia spp. taxonomy and distribution, life history, ecology and ecosystem services, wild harvest, aquaculture, and commercial applications. We discuss future research directions.
... Vol:. (1234567890) Edwards et al. 2020). Many macroalgal species are considered habitat-formers, which have direct and indirect effects on associated communities by providing food (Schaal et al. 2009) and shelter (Teagle et al. 2016), modifying physical factors such as living space (Crooks 2002), light (Uribe et al. 2015) and water flow (Shelamoff et al. 2019), in addition to contributing to the cycling of energy and matter (Abdullah et al. 2017). As a result, habitat-formers and their associated communities strongly influence ecosystem processes, but these effects can vary among habitat types and times (Cvitkovic et al. 2017). ...
The green macroalga Caulerpa filiformis has been spreading on shallow soft sediment habitats along the Peruvian coast, colonizing previously unvegetated sediments to create monospecific meadows. We examined the nature of the impact of C. filiformis meadows on the density, taxonomic richness and assemblage structure of epifaunal and infaunal
benthic macroinvertebrates. Specifically, we tested whether the spread of C. filiformis has resulted in different macroinvertebrate assemblages than those formed by the dominant native macroalgae (i.e., Rhodymenia spp.) and unvegetated sediments. Surveys were undertaken in two bays in each of two locations, in central and southern Peru, during winter 2017 and summer 2018. In general, our results show that macroinvertebrate assemblages were similar across all three habitats, although there were some differences , related to location and time, but with no clear patterns observed. Taxonomic richness and density was generally higher in the vegetated habitats than the unvegetated habitat, and where there were differences between the two vegetated habitats there was no consistent pattern of which habitat supported the highest richness or density. Given invading C. fili-formis is primarily colonizing unvegetated habitats it would appear that this species is creating a new niche which supports similar assemblages, but higher taxo-nomic richness and density than unvegetated habitats. While our study suggests that C. filiformis is having a limited ecological impact we recommend that actions be put in place to limit the spread of this invasive species at the same time as increasing monitoring of the ecological impacts of this species as lags in the ecological impacts of invasive species are common.
... Habitat-forming species are important to the structure and functioning of marine ecosystems as they often result in altered local environmental conditions and high levels of biodiversity (Teagle et al. 2016;Edwards et al. 2020). Many macroalgal species are considered habitat-formers, which have direct and indirect effects on associated communities by providing food (Schaal et al. 2009) and shelter (Teagle et al. 2016), modifying physical factors such as living space (Crooks 2002), light (Uribe et al. 2015) and water ow (Shelamoff et al. 2019), in addition to contributing to the cycling of energy and matter (Abdullah et al. 2017). As a result, habitat-formers and their associated communities strongly in uence ecosystem processes, but these effects can vary among habitat types and times (Cvitkovic et al. 2017). ...
The green macroalga Caulerpa filiformis has been spreading on shallow soft sediment habitats along the Peruvian coast, colonizing previously unvegetated sediments to create monospecific meadows. We examined the nature of the impact of C. filiformis meadows on the density, taxonomic richness and assemblage structure of epifaunal and infaunal benthic macroinvertebrates. Specifically, we tested whether the spread of C. filiformis has resulted in different macroinvertebrate assemblages than those formed by the dominant native macroalgae (i.e., Rhodymenia spp.) and unvegetated sediments. Surveys were undertaken in two bays in each of two locations, in central and southern Peru, during winter 2017 and summer 2018. In general, our results show that macroinvertebrate assemblages were similar across all three habitats, although there were some differences, related to location and season, but with no clear patterns observed. Taxonomic richness and density was generally higher in the vegetated habitats than the unvegetated habitat, and where there were differences between the two vegetated habitats there was no consistent pattern of which habitat supported the highest richness or density. Given invading C. filiformis is primarily colonizing unvegetated habitats it would appear that this species is creating a new niche which supports similar assemblages, but higher taxonomic richness and density than unvegetated habitats. While our study suggests that C. filiformis is having a limited ecological impact we recommend that actions be put in place to limit the spread of this invasive species at the same time as increasing monitoring of the ecological impacts of this species as lags in the ecological impacts of invasive species are common.
... A third fenced treatment (semi-caged), with 1 × 1-cm mesh side fences but no top, was deployed to separate the effects of benthic herbivores (e.g., sea urchins, mollusks) from fishes. We deployed five replicates of each treatment since environmental hazards and human intervention could possibly result in the loss of plates and therefore hopefully maintaining a minimum of three replicates per site (Friedlander and Brown 2005;Uribe et al. 2015). A fourth treatment with a top but no side fences was employed to eliminate fish herbivory and allow invertebrate grazing. ...
Species overexploitation has simplified food webs worldwide, resulting in the degradation of ecosystems relative to their natural state. Fishes are the most important herbivores in many shallow coral reef environments, where they control algal successional processes and promote coral reef resilience. Nowadays, Rapa Nui (Easter Island) is suffering a severe decline in its nearshore fish populations due to overfishing. In this study, we used artificial underwater settlement plates with different levels of herbivore exclusion, and underwater visual censuses, for eight consecutive months to examine the functional role of herbivorous fishes in the coastal benthic community of Rapa Nui. Fishes effectively controlled fleshy erect algae growth along the west and north coast of the island. In total exclusion treatments, Codium spp. dominated settlement plates, showing a likely late successional stage when no herbivory occurred. Significant differences in fish biomass were observed across sites, suggesting a possible fishing gradient. The results of this study can help to inform various spatial and temporal management strategies to increase the protection of nearshore fishes at the recently created Rapa Nui multiple-use marine protected area.
... This kelp is the most abundant brown macroalgae in subtidal environments throughout much of the Chilean coast (18-42 • S) [2,3]. L. trabeculata supports essential ecological assemblages, forming habitats [4][5][6][7] and providing services and ecosystem functions, such as food sources and shelters for different species of invertebrates and fish [8,9,12] and a reduction of wave intensity and water flow [13,14]. ...
Subtidal Lessonia trabeculata is one of the primary kelp resources of northern Chile. It is an ecosystem engineer that provides habitat, shelter, and food for invertebrates and fish. This fishery has been developed by a collection of stranded algae carried out by legally registered fishers and illegal collectors in open-access areas and man-agement and exploitation areas for benthic resources. Due to the current high demand on the international market, the collection of dead plants is supplemented by direct extraction. In response, a management plan has been implemented to regulate extraction efforts and institute annual quotas. The dynamics of the L. trabeculata fishery in the Atacama region over 20 years were evaluated using the conceptual framework of the driver- pressure-state-impact-response (DPSIR) approach. The fishing dynamics are strongly conditioned by price fluc-tuations, promoting the growth of fishing efforts (pressure) in response to economic indicators (driving forces). This often leads to a high volume of extractions of resources (impact) reflected in the increase in extractors and landings in spite of the establishment of quotas (responses), that generate intense pressure on local populations of algae and other commercially important fish and invertebrates (state). A lack of knowledge was detected regarding population aspects and its associated communities. Consequently, this kelp has been mismanaged without a specific focus on this species. Finally, the indicators included in the present DPSIR analysis enable a global understanding of the L. trabeculata fishery, and it should be considered as a basis for future studies and the implementation of resource management strategies.
... Chilean kelps support a vast biodiversity and marine stocking has the potential to restore these communities and ecosystems. Several studies have shown that at least six species of fishes (including sharks) and approximately 50 taxa of invertebrates depend on the habitat provided by kelps to reproduce and thrive (Thiel and Vásquez 2000, Vásquez and Vega 2005, Uribe et al. 2015, Trujillo et al. 2019, Villegas et al. 2019. Theoretically, kelp stocking will not only improve harvest of kelp species for export, but also support recovery and/or enhancement of other desirable species for artisanal fisheries, such as sea urchins and gastropods. ...
Chile has a long history of restocking, stock enhancement, and translocation to support artisanal or small-scale fisheries; however, these programs have been scarcely discussed in the scientific literature. Here, we present a review of previous initiatives and discuss specific areas for future progress. We identified 204 releases across 117 different areas, involving 7 taxonomic groups and 22 species (20 marine and 2 freshwater). Marine stocking mainly occurred within the context of the spatial framework through which artisanal fisheries are managed [Management and Exploitation Areas for Benthic Resources (MEABR)], and over 60% involved translocation of wild individuals rather than release of hatchery-reared seed. While “stock enhancement” was the primary intention for most releases, it is unclear whether depleted spawning biomass or other recruitment limitations were the primary motivation, and few projects reported more than one stocking event. The echinoid Loxechinus albus and the gastropod Concholepas concholepas were the main target species. Only 6% of projects examined reported positive results that could be linked to releases, and none reported the use of tagging or analysis of costs or benefits. There are several areas for targeted development that should improve the social and economic outcomes from marine stocking activities. This synthesis provides a snapshot of marine stocking in Chile to date and highlights opportunities that are relevant to both Chile and other nations with substantial small-scale fisheries.
... a priori, these new approaches for the study of marine hard bottoms may seem less accurate and less precise in the quantification of the components of the samples than those more standardized and common methodologies (e.g., small and manageable sampling units). nevertheless, most studies about benthic communities analyze the obtained data of abundances after a square root, fourth root or log transformation (Connell & Glasby 1999, Glasby & Connell 2001, Fraschetti et al. 2002, Anderson et al. 2004, Walker & Schlacher 2014, Uribe et al. 2015. ...
Marine hard bottoms support the highest proportion of marine biodiversity. In addition, there are a wide range of sizes and forms among the benthic species of a hard bottom community: solitary or modular, from small organisms to large erected colonies, epibionts, encrusting fauna, mobile predators, etc. These habitats and their biological communities have a high heterogeneity at different spatio-temporal scales. The high diversity and heterogeneity of the hard bottom habitats can present considerable difficulties to obtain accurate and statistically comparable data for community monitoring. Thus, marine hard bottoms are complex habitats where monitoring protocols vary considerably. We review the main approaches used in the study of this type of habitat, assessing some of their main advantages and disadvantages, and highlight a not sufficiently explored alternative where the sampling effort is controlled by a set period of sampling time. Time-constrained searches have been routinely used in terrestrial ecological studies but few explore in marine habitats. However, it is an acceptable alternative that would be worth further exploring for studding marine hard bottom communities. Time-constrained meth- odology presents a good cost-benefit balance: It provides a good representation of the diversity of hard bottom communities, the costs (both in time and economic resources) for sampling and sorting are lower, and the quantification of taxa allows their relative abundance to influence the results
... This outcome also agrees with , who reported that this sea urchin is a part of the KSCs in kelp forests of benthic ecosystems of Mejillones Peninsula (northern Chile). This sea urchin is a conspicuous benthic grazer; it is one of the most abundant grazers along the north-central coast of Chile and dominates in the barrens (Steneck et al., 2002;Tegner & Dayton, 2000;Uribe, Ortiz, Macaya, & Pacheco, 2015;Vásquez & Buschmann, 1997). Therefore, changes in abundance of this sea urchin and the intensive exploitation of kelp could eventually have synergetic negative impacts on the kelp forest ecosystem along the north-central Chilean coast (Ortiz, 2003;Vásquez, 2008;Vásquez et al., 2013). ...
The book presents a collection of large-scale network-modeling studies on coastal systems in Latin America. It includes a novel description of the functioning of coastal complex ecosystems and also predicts how natural and human-made disturbances percolate through the networks. Coastal areas belong to the most populated ecosystems around the globe, and are massively influenced by human impacts such as shipping, mining, fisheries, tourism, pollution and human settlements. Even though many of these activities have facilitated socio-economic development, they have also caused a significant deterioration in natural populations, communities and ecosystems worldwide.
Covering coastal marine ecosystems of Latin America such as the NE and SE Pacific, NW Atlantic and Caribbean areas, it discusses the construction of quantitative (Ecopath-Ecosim-Ecospace and Centrality of Node Sets) and semi-quantitative (Loop Analysis) multispecies trophic-network models to describe and assess the impacts of natural and human interventions like pelagic and benthic fishing as well as natural events such as El Niño, and La Niña. The book also features steady state (and/or near moving equilibrium) and dynamical models to support the management of exploited organisms, and applies and quantifies macroscopic indices, based on Ascendency (Ulanowicz) and Local Stability (Levins´ Loop Analysis). Further, it discusses the determination of the Keystone Species Complex Index, which is a holistic extension of the classical concept of Keystone Species (Paine), offering novel strategies for conservation monitoring and management.
... This outcome also agrees with , who reported that this sea urchin is a part of the KSCs in kelp forests of benthic ecosystems of Mejillones Peninsula (northern Chile). This sea urchin is a conspicuous benthic grazer; it is one of the most abundant grazers along the north-central coast of Chile and dominates in the barrens (Steneck et al., 2002;Tegner & Dayton, 2000;Uribe, Ortiz, Macaya, & Pacheco, 2015;Vásquez & Buschmann, 1997). Therefore, changes in abundance of this sea urchin and the intensive exploitation of kelp could eventually have synergetic negative impacts on the kelp forest ecosystem along the north-central Chilean coast (Ortiz, 2003;Vásquez, 2008;Vásquez et al., 2013). ...
A main objective of fisheries management is to regulate fishing mortality rates in order to achieve objectives of economic, social and ecological sustainability. Tongoy Bay is a high biological productive area that supports an important artisanal benthic fishery. The highest catch take place in the late 1990s, since then Tongoy Bay has been under a fishing control regime, as a consequence of the Implementation of Territorial Uses Rights for Fisheries (TURFs), showing signs of improvement in the health status of whole communities. To establish the level of sustainability in long term of the benthic ecosystem, three stationary trophic models (using Ecopath) were building for the years 1992, 2002 and 2012. Fisheries management strategies were evaluated for economic and ecological objectives through dynamic trophic models (Ecosim), which were optimized based on changes in fishing mortality of the exploited resources. The main result showed that high fishing mortality rates are associated with greater economic value but have negatively effect on the structure of the ecosystem. Conversely, giving greater weight to ecological objectives results in strong negative effects on economic objectives. The evaluation of both criteria simultaneously allows establishing criteria that responds to optimum results for both criteria used. However, the optimization responses of both objective functions were notably affected by the ecosystem health condition of each year/model. In 1992, for which the lowest health ecosystem was established, showed a lower ecological sustainability and low potential for economic optimization compared to the year 2012, which presented a better ecosystem condition. We concluded that sustainability and optimization based on the potential of ecological and economic is a condition related by the degree of exploitation in benthic ecosystem. Therefore, before seeking to optimize the productivity of the system, its health should be recovered.
... This outcome also agrees with , who reported that this sea urchin is a part of the KSCs in kelp forests of benthic ecosystems of Mejillones Peninsula (northern Chile). This sea urchin is a conspicuous benthic grazer; it is one of the most abundant grazers along the north-central coast of Chile and dominates in the barrens (Steneck et al., 2002;Tegner & Dayton, 2000;Uribe, Ortiz, Macaya, & Pacheco, 2015;Vásquez & Buschmann, 1997). Therefore, changes in abundance of this sea urchin and the intensive exploitation of kelp could eventually have synergetic negative impacts on the kelp forest ecosystem along the north-central Chilean coast (Ortiz, 2003;Vásquez, 2008;Vásquez et al., 2013). ...
The Humboldt Current Large Marine Ecosystem (HCLME) is a salient feature of the southeastern Pacific, along the South American coast of Chile and Peru. It is associated with coastal upwelling which generates a very productive ecosystem. However, due to a variety of interconnected biophysical processes at diverse temporal and spatial scales, production varies greatly in time and space. The interplay of the biophysical environment, biological processes involving valuable resources on international markets, the socio-political context, and some management decisions, has shaped the daily life of the HCLME fisheries, marked by booms and busts, offering wealth for short periods of time, followed by collapses. These collapses are generally interpreted as the consequence of a lack of appropriate management, so that a variety of increasingly stricter regulations have been implemented. Nevertheless, this has not significantly reduced the temporal variability of the fisheries landings, which is broadly characterized by a peaks and troughs pattern. While the HCLME is one of the most productive marine ecosystems on Earth, along with a great biophysical and biological variability, it is also a huge but fragile exploited social-ecological system. Modelers can help to understand how to continuously adapt in order to deal with recurrent fisheries “crises,” which, as we are beginning to learn, may simply be an expression of the variability inherent in this complex system. Furthermore, it is essential to increase our capacity to adapt to the expected consequences of climate change.
... This outcome also agrees with , who reported that this sea urchin is a part of the KSCs in kelp forests of benthic ecosystems of Mejillones Peninsula (northern Chile). This sea urchin is a conspicuous benthic grazer; it is one of the most abundant grazers along the north-central coast of Chile and dominates in the barrens (Steneck et al., 2002;Tegner & Dayton, 2000;Uribe, Ortiz, Macaya, & Pacheco, 2015;Vásquez & Buschmann, 1997). Therefore, changes in abundance of this sea urchin and the intensive exploitation of kelp could eventually have synergetic negative impacts on the kelp forest ecosystem along the north-central Chilean coast (Ortiz, 2003;Vásquez, 2008;Vásquez et al., 2013). ...
Banco Chinchorro coral reef is an important protected marine area in Mexico, due to its biodiversity and ecosystem services, which has experienced overfishing of Lobatus gigas, Panulirus argus, and several target fish species. We aimed to build a model that was balanced (Ecopath) and spatially-explicit (Ecospace) to assess the application of different management strategies on the ecosystem. The spatial model for Banco Chinchorro reef distinguished the following five subsystems: Cueva de Tiburones, La Caldera, La Baliza, El Colorado, and El Chankay. Outcomes showed that benthic autotrophs comprised of the highest biomass in the whole system, followed by small benthic epifauna and sponges. Concerning ecosystem growth and development, Banco Chinchorro reef achieved a Total System Throughput of 144,980.7 g ww m⁻² year⁻¹, an Ascendency of 184,988.0 g ww m⁻² year⁻¹*bit, and a Development Capacity equal to 304,287.4 g ww m⁻² year⁻¹*bits. The A/C and Ov/C ratios reached 40.69% and 59.31%, respectively. The mean trophic level of the catch was estimated as 3.09, indicating that fishing is concentrated on species located at a high trophic level. Spatial-dynamic simulations showed that exploitation exerted separately, by subsystem, resulted in higher direct and indirect effects than fishing throughout the whole ecosystem. These results suggest that habitat rotation for harvest would not be advised.
... This outcome also agrees with , who reported that this sea urchin is a part of the KSCs in kelp forests of benthic ecosystems of Mejillones Peninsula (northern Chile). This sea urchin is a conspicuous benthic grazer; it is one of the most abundant grazers along the north-central coast of Chile and dominates in the barrens (Steneck et al., 2002;Tegner & Dayton, 2000;Uribe, Ortiz, Macaya, & Pacheco, 2015;Vásquez & Buschmann, 1997). Therefore, changes in abundance of this sea urchin and the intensive exploitation of kelp could eventually have synergetic negative impacts on the kelp forest ecosystem along the north-central Chilean coast (Ortiz, 2003;Vásquez, 2008;Vásquez et al., 2013). ...
Benthic ecosystems along the north-central Chilean coast are characterised by the presence of kelp forests, considered as ecosystem engineer or niche constructor organisms. Despite their essential ecological role, in the last years kelp forests have been heavily exploited and disturbed by artisanal fishing, inducing drastic changes in such benthic communities and altering the structure and functioning of ecosystem properties. The kelp forest ecosystem gives shelter to a rich community of interacting species. Therefore, any natural or anthropogenic perturbation will affect, directly or indirectly, several components of their interaction network. This can be monitored by holistic, macroscopic indicators. Multispecies trophic network analyses allow us (1) to identify core species or functional groups that play key roles in these ecosystems, named as Keystone Species Complex (KSC) and (2) to quantify macroscopic properties of ecosystems that quantify structure, organisation and health. For the former task, we perform topological analysis and identify the most central sets of nodes. For the latter task, we compute Ascendency, based on thermodynamic laws and information theory and Loop Analysis, based on semi-quantitative community matrices. Using these frameworks, we contribute to the improvement of the current management strategies of artisanal fisheries, conservation and monitoring programmes.
... This outcome also agrees with , who reported that this sea urchin is a part of the KSCs in kelp forests of benthic ecosystems of Mejillones Peninsula (northern Chile). This sea urchin is a conspicuous benthic grazer; it is one of the most abundant grazers along the north-central coast of Chile and dominates in the barrens (Steneck et al., 2002;Tegner & Dayton, 2000;Uribe, Ortiz, Macaya, & Pacheco, 2015;Vásquez & Buschmann, 1997). Therefore, changes in abundance of this sea urchin and the intensive exploitation of kelp could eventually have synergetic negative impacts on the kelp forest ecosystem along the north-central Chilean coast (Ortiz, 2003;Vásquez, 2008;Vásquez et al., 2013). ...
Anthropogenic pressures threaten marine biodiversity at multiple scales and challenge scientists to understand and mitigate human impacts on marine biodiversity. Facing such a challenge, recent approaches that bridge community ecology and conservation planning can broaden the theoretical foundations of strategies aimed to ensure the resilience and functional diversity of marine food webs. We here summarize metrics used to describe patterns of ecological interactions that account for the overall community architecture, such as nestedness and modularity. In addition, we discuss approaches to characterize species topological roles within food webs in order to identify sets of interacting species that act as the backbone of marine biodiversity and ecosystem functions. We argue that combining empirical data and dynamic network modeling is key to foster the integrative understanding of ecological, evolutionary, and anthropogenic processes shaping marine food webs, which requires theoretical ecologists and practitioners to work together in long-term, system-level strategies to conserve marine biodiversity and improve the sustainability of fisheries.
... We applied the non-parametric and two-way crossed permutational multivariate analysis of variance (PERMANOVA) considering the period of application of our questionnaire (initial and final) and gender as fixed factors. PERMANOVA is robust for non-normal distributions and univariate analysis applied to Euclidean distance matrices (Anderson et al., 2008;Uribe et al., 2015). The critical level (α) was set at 95% of confidence interval (α = 0.05). ...
Effective ocean literacy requires appropriate individual behavior, but achieving
this—based on behavior change—is extremely difficult. Social-psychological research
shows that even generating knowledge and awareness toward protecting the
environment—including the oceans—very rarely produces behavior change. The
correlation between knowledge and behavior change is demonstrably surprisingly low.
Based upon a systematic interdisciplinary literature review, this article evaluates the
factors constituting behavior that are important for ocean literacy. Furthermore, it includes
an analysis of options for individual behavior change. The literature review covers
research and theories from behavioral sciences such as social, environmental, and
emotional psychology, as well as from other social sciences. Specifically, research on
pro-environmental behavior is evaluated and applied to the specific case of ocean-related
behaviors and ocean literacy. As a result, the model of pro-environmental behavior by
Kollmuss and Agyeman has successfully been transferred to increase the effectiveness
of ocean literacy because it considers internal (e.g., emotions and values) and external
factors (e.g., politico-economic and socio-cultural), which are crucial to achieve behavior
change. Further results show that the theoretical analysis of different influence factors of
ocean related behavior help to identify options to enhance ocean literacy, partially not yet
broadly applied in this field, such as reputation-based incentives, social marketing, and
successfully diffusing social change, which is illustrated within two examples of success
stories. Nevertheless, improvements remain challenging due to barriers identified on
the individual level (e.g., cognitive dissonance and moral disengagement) and adverse
political and economic power relations in light of rapidly increasing environmental
problems in our oceans.
... We applied the non-parametric and two-way crossed permutational multivariate analysis of variance (PERMANOVA) considering the period of application of our questionnaire (initial and final) and gender as fixed factors. PERMANOVA is robust for non-normal distributions and univariate analysis applied to Euclidean distance matrices (Anderson et al., 2008;Uribe et al., 2015). The critical level (α) was set at 95% of confidence interval (α = 0.05). ...
... These patterns were related to the age of the fish. Therefore, we provide support for the idea that the ecological theory of succession extensively described for freeliving communities (Clarke et al. 1993;Wahl et al. 2013;Uribe et al. 2015;Guerra-Castro & Cruz-Motta, 2018) also applies for parasite communities as well, highlighting the robustness of this theory in ecology. ...
Parasite communities are similar to free‐living communities; decay of similarity over geographic distance, theory of island biogeography, species–area relationships and nestedness have been documented in both communities. Ecological succession has been studied in free‐living communities but has rarely been examined in parasite communities. We use seriation with replication to test the hypothesis that succession of parasite community structure is deterministic, thus developing throughout consecutive changes along the fish ontogeny, via a seriated pattern. 12 306 marine fishes (95 species) were studied. In 40 species, a seriated pattern was detected; 25 had a tendency towards a seriated pattern, and for 31 species, succession was at random. Age‐classes for each host species explained deterministic successional patterns for whole parasite communities and ectoparasites. Richness and number of age‐classes explained this pattern for endoparasites. Seriated successional pattern was evident for parasite communities of long‐lived marine fish, indicating that parasite communities follow sequential changes over time, like many free‐living communities.
... Many species and communities have extensive geographic distributions along the Humboldt Current System, which is characterized by high primary and secondary productivity due to intense and year-round upwelling ). Subtidal habitats comprise extensive rocky reefs with seaweed beds (Aguilera et al. 2019), including large kelps such as Lessonia trabeculata or Macrocystis pyrifera (Macaya and Zuccarello 2010;Uribe et al. 2015), or barren grounds dominated by sea urchins (Tetrapygus niger) or snails (Tegula sp.) and covered by crustose calcareous algae (Stotz et al. 2016). Species composition is relatively consistent along the continental coast of Chile (between 18°S and 42°S), and the most important predators are fishes , such as Cheilodactylus variegatus, Pinguipes chilensis, Graus nigra, Semicossyphus darwini and others (Pérez-Matus et al. 2007), and invertebrates such as the crustaceans Romaleon setosum (Fischer and Thatje 2008;Pacheco et al. 2013) and Homalaspis plana (Fernández and Castilla 2000), the seastar Meyenaster gelatinosus (Urriago et al. 2011), Heliaster helianthus (Gaymer and Himmelman 2008), and the mollusc Concholepas concholepas (Dye 1991). ...
Consumer pressure in benthic communities is predicted to be higher at low than at high latitudes, but support for this pattern has been ambiguous, especially for herbivory. To understand large-scale variation in biotic interactions, we quantify consumption (predation and herbivory) along 2500 km of the Chilean coast (19°S–42°S). We deployed tethering assays at ten sites with three different baits: the crab Petrolisthes laevigatus as living prey for predators, dried squid as dead prey for predators/scavengers, and the kelp Lessonia spp. for herbivores. Underwater videos were used to characterize the consumer community and identify those species consuming baits. The species composition of consumers, frequency of occurrence, and maximum abundance (MaxN) of crustaceans and the blenniid fish Scartichthys spp. varied across sites. Consumption of P. laevigatus and kelp did not vary with latitude, while squid baits were consumed more quickly at mid and high latitudes. This is likely explained by the increased occurrence of predatory crabs, which was positively correlated with consumption of squidpops after 2 h. Crabs, rather than fish, were the principal consumers of squid baits (91% of all recorded predation events) at sites south of 30°S. Fish and crustaceans preyed in similar proportion on P. laevigatus, with most fish predation events at northern sites. The absence of any strong latitudinal patterns in consumption rate of tethered prey is likely due to redundancy among consumers across the latitudinal range, with crustaceans gaining in importance with increasing latitude, possibly replacing fish as key predators.
... We applied the non-parametric and two-way crossed permutational multivariate analysis of variance (PERMANOVA) considering the period of application of our questionnaire (initial and final) and gender as fixed factors. PERMANOVA is robust for non-normal distributions and univariate analysis applied to Euclidean distance matrices (Anderson et al., 2008;Uribe et al., 2015). The critical level (α) was set at 95% of confidence interval (α = 0.05). ...
While increasing awareness about ocean-related topics is a matter of urgent necessity, ocean and coastal-literate schoolchildren are uncommon in Brazil, even in coastal cities. In the present study, we report the activities of an environmental education project spanning a 3-year period in São Vicente, a city surrounded by marine habitats in the southeastern state of São Paulo. This project was part of a university initiative aiming to promote shared knowledge between marine biology student-monitors and the encircling community. With the aid of informal and practical educational activities, we introduced topics of marine zoology, marine ecology, waste management and recycling to 200 fifth-year primary students. Using pre- and post-instructional questionnaires, we evaluated the students’ general knowledge of provided ocean and coastal literacy topics. Our results showed a significant difference between initial and final perception across all questions, with a higher questionnaire score after activities. The highest increase in perception concerned lessons on the marine fauna found around the school (94.6% from the initial 7.9%), pointing to the intrinsic value of teaching biological sciences from a zoological perspective. Increased knowledge retention was also observed in lessons on pollution (52.6% from 26.7%), recycling (77.2% from 61.9%), and regional waste treatment (51.8% from 24.2%). Overall, this initiative proved to be a fruitful addition to the school curriculum, especially considering the relevance of rapid urbanization, environmental degradation and water pollution in São Vicente and the role these children might exert as critical-thinking citizens in the future. On the other end, our monitors were also provided with the opportunity for an informal teaching environment complementary to their usual academic-centric degree, with a fresh perspective on accessible scientific communication.
... It is characterized by rocky bottom, barren ground and kelp forests of Lessonia trabeculata and Macrocystis integrifolia. The bathymetry does not exceed 18 m (Uribe et al., 2015). ...
The early life history traits of the labrisomid blenny Auchenionchus crinitus (Jenyns, 1842) from subtidal rocky reefs were studied, based on microstructure analysis of sagittae of their pelagic larvae (4.01 mm NL −12.50 mm SL). Ichthyoplankton was collected in shallow (<20 m) nearshore waters off Isla Santa María, Antofagasta, northern Chile every 15 days during austral autumn–winter 2014 (five sampling days). During late May and early June, larval abundance was low (median ± MAD, 39.06 ± 5.08 ind. 100 m ⁻³ ), increasing significantly during mid-June to early August (110.98 ± 47.66 ind. 100 m ⁻³ ). Using 354 sagittae, the back-calculated hatch dates indicated the occurrence of three hatching events, two in autumn and one in winter. Hatching occurred mainly during the illuminated phases of the lunar cycle. All three batches had similar estimated larval sizes at hatch (3.2–3.7 mm SL), as well as similar growth rates (0.19–0.22 mm day ⁻¹ ) during the first 30 days of life. During the study period, shallow waters were well mixed, with seawater temperature of 14.73 ± 0.58°C and salinity of 34.84 ± 0.04. This is the first estimation of early life history traits of this cryptobenthic species from rocky reefs of Chile.
... Both sea urchin species are conspicuous benthic grazers. Tetrapygus niger is one of the most abundant grazers along the north-central coast of Chile and dominates in the barrens (Steneck et al., 2002;Tegner and Dayton, 2000;Uribe et al., 2015;Vásquez and Buschmann, 1997), while L. albus is one of the most economically important species (Vásquez and Buschmann, 1997). In this sense, our results are relevant because changes in the abundance of both sea urchins could also be indirect consequences of the intensive exploitation of kelp species that is taking place along the north-central Chilean coast (Ortiz, 2003;Ortiz and Levins, 2017;Vásquez et al., 2013;Vásquez, 2008). ...
... The temporal variation and distributional pattern of marine communities are the reflection of self-adaption for the ecosystem to the changing conditions (Baker and Pak 1990). Marine communities show a significant temporal variation in the species composition and biomass to maintain the stability of ecosystem (Uribe et al. 2015). Temporal variation is common for many macroalgae and epiphytic faunas for their short lifespan. ...
Epiphytic fauna community structure is mainly determined by macro-scale environmental characteristics (e.g., water motion), whereas the influences of, and interaction with, micro-scale habitat-forming species are not well known. In order to explore the effects of water motion and functional macroalgal group on the community structure of epiphytic faunas, macroalgae and epiphytic faunas from four isolated artificial rocky reefs with different levels of hydrodynamic conditions were investigated in Laoshan Bay of China. A total of 32 macroalgal species and 22 faunal species were recorded on the surveys. The biomass and abundance of macroalgae and epiphytic faunas showed significant variations among stations and months. The biomass and abundance of epiphytic faunas were highest at outer Huangshankou station (H1) with medium hydrodynamic force. The lowest biomass of epiphytic faunas occurred at inner Huangshankou station (H3) with highest level of water motion, while the lowest abundance of epiphytic faunas occurred at Liepo station (L) with lowest level of water motion. Results showed that medium water motion level contributed to increasing biodiversity of epiphytic faunas. Epiphytic communities generally presented higher biomass and abundance in summer than in spring or autumn, which indicated temperature could be the ecological driver for temporal variation of epiphytic communities. The epiphytic faunas showed distinct preferences to structural morphology of macroalgae which forms suitable habitat for these organisms. This study suggests that artificial rocky reefs are of great significance to restore and maintain coastal biodiversity, and appropriate physical disturbance promote community reestablishment.
... It is therefore important to describe and understand the processes of succession and how these are affected by global change Dijkstra et al. 2011;Prach and Walker 2011;Meiners et al. 2015). Even though succession trajectories in the subtidal have been documented for marine hard-bottom algal communities (Sousa 2001;Noël et al. 2009;Pacheco et al. 2011;Hurd et al. 2014;Uribe et al. 2015), information on patterns of succession of benthic communities in Antarctica come mainly from faunal assemblages (Barnes et al. 1996;Stanwell-Smith and Barnes 1997;Bowden et al. 2006; Barnes and Conlan 2007;Lagger et al. 2017). The latter reveal either a rather predictable succession as a result of slow growth and strong environmental seasonality (Bowden et al. 2006) or internannual massive events of colonization (Dayton 1989). ...
There is a general lack of information on the succession of marine benthic algae in Antarctica. We performed two colonization experiments in the upper subtidal (3 and 5 m depth) using artificial substrates in Potter Cove (South Shetland Islands): in the outer cove, an area mainly unaffected by sedimentation, and in the inner cove, in close proximity to a retreating glacier, with high sediment inflow particularly during the melting season. Seasonal and interannual changes in total, diatom and macroalgal cover, species composition, and ecological indexes were assessed over four years. Tiles were analysed in spring and summer in the laboratory and by year-round photographic monitoring. Irradiance (photosynthetically active radiation and ultraviolet radiation), salinity, and temperature were monitored on a monthly basis. Benthic algae dominated the assemblages, with macroalgae reaching ~70% cover after two years. There were site and temporal differences in the contribution of diatom mats (mainly pennate forms) and macroalgal cover. Diatom cover was higher at the glacier-influenced site, particularly at the early stages, and decreased significantly with time. Between years, macroalgal assemblages changed significantly in a site-specific manner. Assemblages mainly comprised annual and pseudoperennial species at both sites, with absence of adult large Desmarestiales. Although a year separated the establishment of the two experiments, there were convergence patterns in the changes of cover over time—that seemed to be controlled by competitive interactions—and in the patterns of species replacement. However, the inner cove site exhibited lower number of macroalgal taxa and a tendency to decreased diversity over time that could be related to higher level of stress and disturbance caused by glacial influence.
... Kelp forests can also act as wave barriers, slowing down currents, retaining propagules and forcing larvae to settle (Morton & Anderson 2013). It has also been suggested that kelp forests may affect recruitment of certain species differently inside and outside the kelp beds (see Almanza et al. 2012;Uribe et al. 2015), with the three-dimensional shape (i.e. structural complexity) significantly mediating availability of suitable substrata for settlers, and consequently altering their probability of survival under different competition or predation pressures ( Besides structural traits, the kelp canopy may also exert some influence on other attractants, including chemical signals (e.g. ...
Identifying patterns of spatial and temporal variability in the composition of communities associated with kelp forests is critical to understand the functioning of this productive, yet vulnerable ecosystem. We used a suite of sampling methods (light attraction and airlift devices) to evaluate the variability of larval, post-larval and macrobenthic assemblages associated with kelp forests (Lessonia trabeculata) in Central Chile (30° to 33 °S). Pelagic collections identified two assemblages: early-life stages and emerging macrobenthos, with the later contributing in three quarters to the total abundance regardless of the source of illumination (permanent or flashing). Field experiments showed that moon phases affected the structure and composition of the samples. Surveys carried out during new moon showed the highest abundances and taxonomic richness of emergent assemblages. However, species composition varied in both assemblages depending on the moon phase. Although the pelagic assemblages collected at sites with contrasting upwelling intensity did not show differences in community structure, differences in composition were evident for early-life stages. The relationship between pelagic and benthic collections indicated that four decapod crustaceans were represented at both larval and early juvenile stages; however, only the high abundances and densities of Paraxanthus barbiger allowed for estimations of benthic-pelagic coupling. For this species, larval abundances and benthic juvenile densities demonstrated contrasting local and regional patterns, suggesting a decoupling between pelagic and benthic environments. These findings highlight the differential variability in smaller components of kelp forests, but also suggest that post-settlement processes may be driving biological interactions through these highly productive and complex environments.
The systematic degradation of marine ecosystems is a global phenomenon that has important consequences including biodiversity loss and reduced ecosystem service provisions. In temperate subtidal regions, kelp forests dominate rocky coasts, and the abundance and resilience of these forests are influenced by local-scale stressors and regional environmental variation. Fisheries is one of the main factors affecting the abundance and persistence of marine ecosystems. Fisheries can directly affect the abundance and population structure of exploited resources (and its associated species), yet it may indirectly affect species interacciones. One clear example of ecosystems affected by direct and indirect effects of fisheries are kelp along the humboldt current system, were fishes and invertebrates inhabiting kelp forests and the kelp forest itself are being degraded by harvesting kelp individuals, an activity localy known as “barreteo”. However, limited information exists regarding the direct and indirect consequences of kelp harvesting which, in turn, limits the ability to provide effective management and conservation efforts. In this thesis I examined the direct and indirect consequences of the artisanal subtidal Lessonia trabeculata fishery and the kelp community of benthic species associated with it along the coast of central Chile.
During a two-year period, I assessed the community level consequences of the direct harvesting of kelp Lessonia trabeculata. In this effort, I assessed (a) the change in adult and juvenile Lessonia trabeculata density as a consequence of harvesting, (b) the impact of Lessonia trabeculata harvesting on reef fish, mobile macroinvertebrate and sessile species assemblages, and (c) the change in density of the most abundant Lessonia trabeculata -associated species. The experiment was conducted from december 2016 to may 2019. In total, after removal of kelp, the size of each plot was ~90m2, and ~90% of Lessonia trabeculata was removed by an experienced kelp fisherman. I used band transects and quadrats to estimate the density of reef fish, mobile macroinvertebrates and the % coverage of sessile species through periodic monitoring previous to and after kelp harvesting in control and harvested plots. The results documented the effects of kelp harvesting by artisanal fishers at a multi-trophic level (from algaes to secondary predators). Even after two years post-harvest, Lessonia trabeculata still shows no signs of recovery. The results indicate that a single, once-off harvesting disturbance from the kelp forest resulted in significant alteration of local reef fish, macrobenthic invertebrate and sessile species assemblages. Previous to harvesting no differences were observed between the assemblages of control and harvested plots. After harvest, within the harvested plots, the average abundance of the fish Scartichthys viridis, the rock shrimp Rhynchocinetes typus and the herbivorous snail Tegula tridentata was greater than non-harvested control plots. On the contrary, a greater abundance in the control plots was observed for the fishes Aplodactylus punctatus, Isacia conceptionis and Chromis crusma. This study also allowed us to evaluate the natural changes in kelp recruitment (i.e. newly settled individuals that have survived one and two years after kelp harvesting, sensu Rodriguez et al., 1993). The difference in abundance of associated species may be key to the lack of recovery of Lessonia trabeculata forests. The study highlights the impact of Lessonia trabeculata harvesting on associated fauna, however, significant knowledge gaps remain, particularly with respect to whether Lessonia trabeculata will fully recover after harvesting and if so, how long will it take to re-establish its original biomass, as well as its associated fauna at the scale at which the fisheries operate.
A second set of studies were developed to evaluate the influence of changes in Lessonia trabeculata kelp forest, mediated by the direct and indirect effects of fisheries, on the recruitment patterns of benthic species. Fisheries can affect kelp forests directly, by altering the density of the forest (i.e. kelp thinning), or indirectly, by removing top predators and altering trophic interactions and ultimately affecting grazing activity on kelp which consequently alters the frondosity of the kelp canopy and ultimately alters the kelps forest complexity. The studies focus on both (a) the direct influence of kelp harvesting and (b) the indirect effect of artisanal fisheries on kelp forest morphology and its consequential effect on the recruitment patterns of benthic species in central Chile. To address the direct effect of Lessonia trabeculata kelp harvesting, recruitment assemblages and recruitment rates of benthic invertebrates were compared between harvested (almost complete kelp removal) and control plots, taking advantage of a large-scale experiment described in the aforementioned study. However, the consequences of harvesting are not necessarily the complete removal of a forest rather the thinning of the density of the kelp forest. Thinning is an expected output of regulated kelp fisheries, since the state suggest to harvest plants sparsely. Thus, the second specific goal evaluated the recruitment patterns (recruitment assemblage and recruitment rate) of benthic invertebrates among three densities of kelp: zero, medium and high. Finally, I assesed the indirect effect of fisheries on recruitment patterns, mediated by changes in kelp morphology. Extense defoliated patches of Lessonia trabeculata have been reported, presumably related to an indirect effect of the depletion of top predators due to coastal fisheries, which ultimately free a top down pressure on herbivores causing a cascading effect that alters the kelp morphology, and reduces its the kelp forests structural complexity. Recruitment assemblage and recruitment rate of benthic invertebrates was evaluated comparing plots of defoliated kelp (no canopy formed, i.e. a “skeleton” morph) and completely foliated natural plots of kelps. Since reproduction of most benthic species in temperate regions is seasonal and hence recruitment, in a first study a full annual cycle was sampled, with one sampling time in each season (autumn, winter, spring and summer) and thus determined the season with greater recruitment of benthic species, and later only evaluated the recruitment in one season for the other two studies, i.e. the austral summer. This set of studies focus exclusively on patterns of recruitment, as a first step to understand the consequences of fisheries. It does not pretend to investigate the processes involved. I used standard monitoring units known as SMURF (standard monituring unit for the recruitment of fish adn invertebrates) to evaluate recruitment. This standard monitorng units were placed in every treatment and later retrieved every couple of weeks. Once in the lab individual recruits where identified to the lowest taxonomical level possible. Recruitment rate of each taxa was measured by dividing the number of individuals per taxa by the number of days that the SMURF were deployed in the field. The results of the studies conducted to assess the direct and indirect effect of fishing activities on Lessonia trabeculata kelp forests showed that (a) kelp harvesting, (b) kelp thinning and (c) kelp morphology affects the recruitment assemblage and the recruitment rate of benthic species. Over 50 taxa were identified and although, the studies were conducted at different sites along the coast of central Chile, and at different time frames, only five species were persistently the most abundant: Eulithidium umbilicata, Pilumnoides perlatus, Taliepus sp., Tetrapygus niger and Semimytilus algosus. These taxa all together represented over 50% of the total number of recruits registered. The results show three general patterns: (a) an effect of the experimental treatments on recruitment assemblage and recruitment rate, reflecting the direct and indirect influence of fisheries on kelp forest complexity and the consequent effect on recruitment assemblage and recruitment rate, (b) different responses in the different studies and species of recruits. These results suggest a need to advance in the management of Lessonia trabeculata fisheries to better account for ecosystem-wide impacts in order to better manage and protect this vital coastal ecosystem.
Estimates suggest that the amount of plastic litter discarded in the ocean is several times greater than what remains floating at the sea surface, raising questions about the fate of this marine debris. Fouling-induced sinking of plastic litter is one of the proposed mechanisms responsible for this mass difference. While some of this ‘missing’ plastic mass may be explained by the effects of fouling, it has also been hypothesized that sinking litter may return to the surface after benthic organisms consume the biofouling. However, this hypothesis has never been tested. The present study evaluated the structure and biomass of the fouling community in response to benthic predation in both summer and winter seasons. Floating PVC plates were installed during winter and summer in central Chile (36°S) until the growing biofouling community caused them to sink. Plates were then moved to the seabed, where they were exposed to benthic predation, while control plates were maintained in a mesh cage impeding predator access. In summer, all plates recovered their buoyancy, while in the winter only 60 % recovered buoyancy. All caged control samples remained on the bottom in both seasons. The community structure differed both in the treatments and across the seasons, with plates that recovered buoyancy initially being dominated by Ulva sp. and Ciona robusta. Conversely, plates that did not refloat were mainly covered by species resistant to predation such as Pyura chilensis, Austromegabalanus psittacus, and Balanus laevis. Thus, fouling community structure influences how predation facilitates buoyancy recovery, because not all epibionts can be consumed by predators. While previous studies had shown how fouling organisms cause sinking of floating litter, this is the first study to provide experimental evidence that predation can reverse this process and allow litter to resurface and become again available as dispersal vectors for native and invasive species.
Manifestations of climate change in the Arctic include an increase in water temperatures and massive loss of sea ice enabling more light penetration. Yet to understand tempo and scale of these parameters change over time, constant monitoring is needed. We present 16-yr long-term datasets of sea water temperature and relative light intensity at two depth strata (8 and 14 ± 1 m) of two hard-bottom sites in southern Isfjorden proper (Spitsbergen, 78°N). The high temporal resolution of the datasets (every 30 min, between 2006–2022) makes them suitable for studying changes at a local scale, correlating environmental variability with observed processes in benthic assemblages, and serving as ground-truth for comparison with, for example, remotely sensed or mooring data. These datasets serve as baseline for long-term investigations in the shallows of a high-Arctic fjord undergoing severe environmental changes.
Marine ecosystems such as kelp are gaining recognition for providing ecosystem services (ES) along the coastal regions worldwide. Here, we synthesize information from the last four decades of research on the structure, functioning and threats of kelp forests, and the ES they provide in the Humboldt Current System (HCS) where information is scarce. The SALSA (Search, Appraisal, Synthesis and Analysis) framework was used for the literature survey and review. From 86 selected articles, only 4 directly discussed kelp ES in Chile. Supporting services-related articles were the most prevalent (n = 59), followed by provisioning (n = 19), regulating (n = 3) and cultural services (n = 1). ES-related research was mostly conducted in Chile (n = 77). Studies in Peru (n = 5), and in Chile and Peru at same time (n = 4) were scarce. Our search also showed that Lessonia trabeculata presented the highest number of associated taxa (n = 213), followed closely by M. pyrifera (n = 210). However, the number of phyla reported was higher in M. pyrifera (n = 17) than in the Lessonia species (n = 7-13). Natural and anthropic impacts on the biodiversity of kelp forests using novel technologies would facilitate the quantitative study and economic valuations of the services provided by these ecosystems at the Humboldt Current System.
Macroscopic ecosystem properties based on an Ascendency theoretical framework were assessed for mass-balance trophic models representing ecological systems constructed by the kelp species Macrocystis pyrifera planted on artificial reefs installed on subtidal barren rocky and sandy bottoms (Antofagasta Peninsula, Chile). Information on biomass, production, diet and consumption was needed. The magnitudes of relative Ascendency, relative Overhead and Redundancy values indicated that kelp planted on artificial reefs allocated on soft bottoms would be more highly developed and less resistant to perturbations than ecological systems on artificial reefs disposed on barren and natural systems inhabiting soft bottoms and kelp habitats. The relative Ascendency corresponding to each component of the ecological systems constructed on artificial reefs on both habitats was represented principally by detritus (∼37%), M. pyrifera (between 22 and 26%) and phytoplankton (between 10 and 13%). The compartments of Rhodophyta, Chlorophyta Mesophyllum sp. and the sea star Heliaster helianthus accounted for the system complexity in terms of flow, exhibiting the lowest Average Mutual Information. The Finn cycling index – considered as a ecosystem maturity index – showed contradictory outcomes compared to Ascendency. However, the values of System omnivory index and Average path length quantified for the ecological systems constructed on both artificial reefs showed similar network topologies compared to natural kelp beds. Based on our findings, artificial reefs seeded with M. pyrifera could be used to restore perturbed local marine benthic ecological systems along the Chilean coast. Likewise, this work shows that the trajectory of local ecological systems can be modified, enhancing their global-system health.
The role of organisms in community assembly and functioning is a crucial question of community ecology. We address this issue in a particular marine coastal ecosystem at SE Pacific: although kelp forests and urchin barrens are conspicuous benthic systems in rocky habitats, only a few studies have been focused on studying their successional patterns (especially following disturbances). In this work, we present successional pathways from micro-periphyton to macro-organisms observed during a 14-month period in kelp forests and urchin barrens in the Antofagasta Peninsula, Chile. The community composition and structure showed habitat-specific successional pathways with different dominant organisms in these two communities. Likewise, during their successional trajectories, both communities showed different number of discrete temporal stages. Kelp forests displayed a longer successional pathway of 7 discrete stages, while the barren bed succession pathway was composed only of 4 stages. We argue that this difference would be due to self-organising processes. This finding may have relevant implications for conservation and monitoring, since the intensive harvest of kelp species will not only increase the dominance of urchin barrens, but it would also facilitate its own, self-determined, more efficient (with few steps) successional pattern and the consequent persistence.
Macro-and micro-environmental factors modulate parasite loads in fish, determining parasitic abundances, diversity, and interaction dynamics. In this study, seasonal variations in larval ectoparasites on fish larvae in the northern Humboldt Current System (HCS) were evaluated using a delta-gamma generalized linear model to predict their occurrence frequencies. Fish larvae were collected from two nearshore areas during austral spring-summer and autumn-winter. Only five (of 38) larval fish species were parasitized by copepods: Gobiesox marmoratus, Ophiogobius jenynsi, Helcogrammoides cunninghami, Myxodes sp., and Auchenionchus crinitus. A binomial model showed that the presence/absence of parasitized fish larvae varied among the fish species and their larval abundances, while a positive delta-gamma model showed that ectoparasite frequency varied among the seasons and fish species. Seasonal variations in parasitized fish larvae frequency could be associated with host and parasite reproductive processes, which are related to oceanographic features responsible for larval retention and subsequent higher infestation probabilities. Host length was positively correlated with ectoparasite length, suggesting early infection and combined growth until the detachment of the ectoparasite. Our results suggest that infestation patterns in larval fish species can be identified using delta-gamma models and that they respond to local (retention) and high-scale (HCS) processes.
Kelps provide important habitat for a range of species, however they are suffering increasing levels of degradation. This has prompted efforts to restore these ecosystems, however, the trajectory of community establishment on artificial reefs has not being widely described. We examined the composition of the species and functional groups of invertebrates and fish in relation to the artificial reefs over soft-bottom and barren-ground habitats over a 10-month period. We evaluated the community structure based on species richness, biomass, species diversity, and dominance of species and functional groups. We assessed the trajectories of the ecological succession of artificial reefs planted with kelp on each bottom type and determined the changes in the dissimilarity of species and functional groups over time. We also analysed the relationship between the biogeny (of macroalgae) over time (months) and the changes in macrobenthic community structure. Successional development of reefs communities was similar across the two habitat types, macroalgae contributed most to the early stage, while invertebrates and fish were the groups that contributed the most during the middle and late successional stages. A positive relationship was found between the presence of artificial reefs with kelp seedlings and the biomass of specific species and functional groups. This study showed that artificial kelp habitats promote the construction of biogenic structures that increase the habitat complexity, promote biodiversity, and increase populations of commercially harvested species. In this sense, artificial kelp reefs should be considered an important tool for restoring the function of degraded benthic ecosystems.
Quantitative and semi-qualitative multispecies trophic network models were used to evaluate the importance of echinoderms to keystone species complexes (KSCs) and their contribution to macroscopic properties in kelp forest ecosystems in the northern Chilean coast. The KSC is a core of species and functional groups playing a key role in the ecosystems. The macroscopic properties quantify the ecosystem’s development, organisation and ‘health’. Dynamical simulations were used to determine the most sensitive species of echinoderms compared to the main carnivores and herbivores in the networks. The echinoderms were present in all the studied KSCs, and their contribution to macroscopic properties was low, except their influence to the ecosystem complexity in comparison to the remaining components of KSCs. The sea star Meyenaster gelatinosus and the sea urchins Tetrapygus niger and Loxechinus albus were the most sensitive species in response to an increase of their total mortality, and the ecosystems would take more time to return to initial steady-state after disturbances. The results indicated that echinoderms play a key role in the benthic ecosystems of kelp forests along northern Chile and principally contribute to the complexity and resistance against perturbations in such ecosystems.
Interactions in the Marine Benthos - edited by Stephen J. Hawkins August 2019
We measured the rate of advance of urchin (Strongylocentrotus droebachiensis) feeding aggregations (fronts) as they destructively grazed kelp beds (Laminaria longicruris) at both a wave-exposed site and a sheltered site in Nova Scotia over 3.5 years. The grazing fronts were composed of high densities of large adults (up to 98 and 70 per 0.25 m(2) at the exposed and sheltered sites, respectively). Urchins in the recently formed barrens, or in adjacent kelp beds, occurred at much lower densities and consisted mainly of juveniles. The fronts moved onshore into shallower water at each site, but their rate of advance varied markedly between sites and over time at each site, ranging from 0 to 4 m.month(-1). The rate of advance of a front was related to the biomass of urchins; fronts did not advance below a threshold biomass of similar to 2 kg.m(-2). Infestations of kelp by an epiphytic bryozoan (Membranipora membranacea) caused marked reductions in kelp canopy cover and biomass during winter, but the canopy regenerated through recruitment of juvenile sporophytes in spring. A localized outbreak of disease decimated S. droebachiensis at the exposed site in 1993, which enabled kelp to recolonize the barrens. Surviving urchins gradually reaggregated and resumed destructive grazing after similar to 1.5 years. A recurrence of disease in 1995 eliminated urchins at both sites and terminated the transition from kelp beds to barrens on a coastal scale. Our findings have important implications for the management of the urchin fishery, which targets grazing fronts for harvesting.
In shallow sublittoral rocky habitats of the Southeast Pacific, two conspicuous ecological systems exist; kelp beds dominated by large Laminariales algae, and barren grounds dominated by crustose coralline algae and sea urchins. The aim of this study was to examine the successional development of micro-periphyton communities in both ecological systems using a colonization experiment conducted in Northern Chile. In both ecological systems, we installed replicated ceramic plates at 10 m depth and samples were taken after 1, 2, 4, 6, 8 and 14 days of exposure. Bacteria, diatoms, protozoans and small eukaryotes were identified, quantified and analysed. The succession of micro-periphyton communities in both ecological systems followed a common pattern consisting of a net accumulation of functional groups and taxa over time; however, the total density of all groups was significantly higher in the kelp beds. In addition, the community structure of the developing micro-periphytons was different and specific for each ecological system. Although previous studies have suggested that kelp beds and barren grounds are capable of switching from one state to the other without substantial changes in biodiversity, our results show that each of these ecological systems promotes its own successional development, suggesting that they are unique, self-organized entities. This study is the first step towards an understanding of these ecological systems operating independently at this scale of organization.
This study used benthic surveys and manipulative experiments to examine (1) if boundaries between kelp forests and urchin barrens exist at multiple locations spanning the Aleutian Archipelago, (2) if these boundaries are spatially stable, and (3) how changes in algal density within the kelp forests influence the ability of urchins to invade them. Our results demonstrate that sharply punctuated kelp forest-urchin barren boundaries occur throughout the Archipelago, and they are spatially stable for at least 2 years. Further, when all macroalgae were experimentally removed from the kelp forest side of the boundaries, urchins rapidly moved into these clearings and excluded macroalgae for up to 2 years. However, these movements were not observed where 75% or less of the macroalgae was removed (leaving 25% or more in place), suggesting that even low macroalgal abundances can prevent urchins from invading the kelp forests. Further, urchin densities were negatively related to kelp density, again indicating that kelp can reduce urchin densities. While the ability of urchins to overgraze kelp forests is widely known, our results indicate that kelp can inhibit urchins, that these inhibitory influences are a widely recurrent phenomenon, and that this interaction is important to maintaining kelp forests across the Aleutians.
Foundation species can provide habitat that modify abiotic and biotic processes that contribute to ecosystem function. While many studies have focused on the processes and consequences of a focal foundation species, understanding the ecological equivalence of co-occurring foundation species is important to identify key species responsible for ecosystem function. Here, we investigated the relative contributions of co-occurring foundation species on abiotic (temperature) and biotic responses of invertebrate species (recruitment, persistence, growth and survival). In a series of experimental field studies, we manipulated foundation species to measure invertebrate recruitment, persistence, and prédation. A laboratory experiment measured foundation species effects on herbivore growth. Results demonstrated that macroalgal (Fucus vesiculosus ecad and Ascophyllum nodosum ecad scorpioides) intermediate foundation species provide habitat, food, and alleviate abiotic stress for dominant littorinid herbivores that surpass that provided by the primary species (Spartina alterniflora). These foundation effects were species-specific with F. vesiculosus ecad important for early life-history stages (enhanced recruitment and early growth of littorinid snails) and A. nodosum ecad important later on as a refuge from predators (Carcinus meanas) and stressful temperature. Understanding of the different effects of co-occurring foundation species on population and community processes is necessary for predicting community response to natural disturbance, species invasion, and ecosystem-based management actions.
ABSTRACT: Overgrazing by sea urchins on temperate reefs can affect a phase shift from macro -
algal beds to ‘barrens’ habitat largely devoid of seaweeds. Existing models of barrens formation
are derived largely from observations of strongylocentrotid urchins, which typically show a
behavioural shift from cryptic feeding to exposed grazing fronts that move through and ‘mow
down’ macroalgal beds. Foraging by the temperate diadematid urchin Centrostephanus rodgersii
triggers a similar transition from intact macroalgal bed to widespread barren grounds but does not
appear to involve a behavioural shift. Fine-scale foraging movements were observed using timelapse
photography across the urchin’s range-extension region and described with respect to a
random walk model. Foraging was highly nocturnal, with individuals homing strongly to available
crevices. In situ monitoring of tagged individuals suggests strong fidelity to and thus high stability
of barren patches, while similar behavioural patterns across habitat types representing a gradient
of foraging intensities indicate no behavioural shift associated with overgrazing. Laboratory
experiments showed that C. rodgersii lacks a directional chemosensory response to either macro -
algae or conspecifics. Combined evidence suggests a model of barrens formation fundamentally
different to the well-established ‘feeding front’ model, with formation of widespread barrens by
C. rodgersii occurring from the ‘inside out’ via growth and coalescence of small barrens patches
that form within macroalgal beds as a result of additive localised grazing radiating from crevice
shelters. Regulation of urchin density at the spatial scale of individual barrens patches is proposed
as a viable option to manage the formation of widespread barrens habitat within the urchin’s
recent range-extension to eastern Tasmania.
The attraction of kelp fauna to different habitat architectures and vertical positions on kelp (Laminaria hyperborea) was tested by colonisation experiments using three artificial habitats (bushy, rough, smooth) at five different vertical positions in a kelp forest. The fauna on epiphytic algae of different structures and at different vertical positions on the kelp was sampled for comparison. Both abundance and number of species were generally highest on bushy substrates, and numbers were significantly highest at the lowest level. The number of species was lowest on smooth substrate, and numbers of individuals increased towards the upper levels on this substrate. The reverse was true on bushy and rough substrates. Amphipods and gastropods were the most numerous groups. Amphipods colonised bushy substrates in higher numbers than smooth. Of the two dominating gastropod species, Rissoa parva was abundant on bushy substrates, mainly in low vertical positions, while Lacuna vincta showed opposite preferences in both habitat selection and vertical distribution. Faunal structure varied along a vertical gradient on natural kelp, and between single epiphytic algal species of different architectures, supporting the results obtained from artificial habitats. Habitat heterogeneity along a vertical gradient within a kelp forest is important for fauna diversity and abundance. The habitat preferences of the fauna may be
related to feeding and predator avoidance strategies.
Habitat complexity plays an important role in the structuring of ecological assemblages in many terrestrial, freshwater and marine habitats. In this study, we investigated the effects of increased habitat complexity on the diversity and abundance of macrofauna colonising artificial kelp holdfasts of 3 varying levels of complexity. The artificial holdfasts were placed within a kelp bed off the coast of Plymouth for 20 d during the summer of 2004. High complexity holdfast mimics were colonised by significantly higher numbers of individuals and species, and had higher species diversity (Shannon-Wiener H'e), than either the medium or low complexity holdfasts. The relationship between habitat complexity and species diversity has often been attributed to a surface area effect, as habitats with a greater complexity generally also have a greater surface area to support a larger number of species. Therefore, we compared the observed community metrics with the values expected if indices were increasing in proportion to the surface area. We found that the number of species and individuals colonising both the medium and high complexity artificial kelp holdfasts were significantly greater than can be explained by a simple surface area relationship. Species diversity increased less rapidly than expected from the surface area relationship, largely because of a dominance effect from a few abundant species of amphipods and gastropods in the high complexity holdfasts. This study demonstrates that the relationship between habitat complexity and species diversity cannot be explained by surface area alone.
Patterns of disturbance and recovery were investigated in algal-dominated littoral rock pools on the west coast of Italy from February 1991 to November 1993. The assemblage was a mosaic of canopy-forming species interspersed amongst patches of turf-forming and encrusting algae. The effects of natural disturbance were investigated by monitoring the size distributions of patches of open space (mainly consisting of encrusting corallines and bare rock) in fixed plots over 2 yr. These plots were distributed in pools maintained at natural and reduced densities of herbivores. In both cases, the mean percentage of open space did not change greatly from February 1991 to February 1993, nor were there differences attributable to grazing by the end of the monitoring period. Shifts in size distributions of natural patches of open space occurred during the 2 yr of observations. The area accounted for by large size-classes (>1200 cm(2)) increased in pools exposed to natural densities of herbivores and decreased in the others. However, grazers never affected size distributions significantly. Overall, results suggested that the provision of open space in this system was mainly due to physical disturbances. A multifactorial experiment was used to assess the effects of herbivores (natural vs reduced densities), size of patch (17 x 17 vs 32 x 32 cm) and time of clearance (February vs August) on algal colonization in experimentally cleared plots. An additional experiment tested for the effects of algal turfs on the establishment of canopy-forming algae in pools where grazers had been removed. The results of the recolonization experiment indicated that herbivores, size of patches and time of clearance exerted important but variable effects on patterns of algal recolonization. Herbivores reduced but could not prevent algal recovery. Their effect was particularly evident for the algal turfs throughout the study, but it was not significant for Cystoseira spp. by the end of the experiment. There were significant size x time of clearance interactions affecting patterns of algal colonization early in the study. The percent cover of turf-forming and canopy-forming plants was greater in the small plots produced in February 1991 than in the other treatments. These effects were more evident in pools exposed to natural densities of grazers and during the early stages of colonization. The results also suggested that competition among Cystoseira spp. and algal turfs was nonhierarchical, the outcome of the interaction depending primarily upon the relative density and life stage of the interacting organisms, rather than on their identity. This view was supported by the fact that established mats of algal turfs drastically inhibited the recruitment of Cystoseira, whilst no strong interaction occurred if recruitment by these species was synchronous. Thus, variability in the intensity and timing of colonization could have important effects for subsequent patterns of algal dominance in this system, but only when grazing was unimportant and algal colonization plentiful. Alternative models were formulated to explain spatial and temporal patterns in pools where these conditions did not occur.
Mass balanced trophic models for kelp ecosystems which include subsystems dominated by Macrocystis integrifolia, Lessonia trabeculata and areas of barren ground (BG) were constructed for subtidal areas near the Mejillones Peninsula (SE Pacific), Chile. Information on biomass, P/B ratios, catches, food spectrum, consumption and dynamics of commercial and non-commercial populations was obtained and examined using Ecopath with Ecosim software analyses. The biomass of blades of L. trabeculata and M. integrifolia represented the compartments most relevant to the subsystems studied. Within the herbivores, the sea urchin Tetrapigus niger was dominant, followed by the snails Turritella sp. and Tegula sp. The fishes Pinguipes chilensis and Cheilodactylus variegatus were the dominant predators, followed by the asteroids Heliaster helianthus and Meyenaster gelatinosus. The highest system throughput (72,512gwetweightm−2year−1) was calculated for the subsystem dominated by M. integrifolia. The mean trophic level of the catch ranged from 1.1 (subsystem dominated by L. trabeculata) to 1.3 (subsystem dominated by M. integrifolia) to 3.2 (barren ground subsystem), showing that harvesting in each system was concentrated either on primary producers (blades of kelp species) or top predator fishes. Although the values for the Relative Ascendency (A/C) fluctuated from 36.5 to 45%, suggesting that all the systems were immature, the subsystem dominated by M. integrifolia emerged as the least resistant to external disturbances (e.g. fisheries). This result agreed with the high value of the system recovery time (SRT) for the M. integrifolia subsystem as a response to combined fisheries scenarios. The results obtained using mixed trophic impact (MTI) and Ecosim [increasing the fishing mortality Fi by 4×] showed that in most of the cases the predictions had the same qualitative tendencies. One of the most important results obtained in this study was that exploitation of kelp blades as an alternative strategy to harvesting the whole plants appeared to be ecologically sustainable, since harvesting the blades propagated only small effects on the entire subsystem. The fish P. chilensis may be considered as a top predator species with a strong top-down control since an increase in its fishing mortality in the subsystem dominated by M. integrifolia produced a high SRT value, and the FMSY was less than the originally entered Fi in Ecopath. Based on the results obtained, it was concluded that the trophic mass balanced models and simulated management scenarios offered good possibilities for the planning of interventions and manipulations or the planning of more sustainable management strategies in highly disturbed natural systems.
I experimentally separated the positive and negative effects of light penetration and sedimentation on the assembly and maintenance of 3 subtidal habitats whose heterogeneity characterizes much of the world's temperate coastline; encrusting (non-geniculate) coralline algae, articulated (geniculate) coralline algae and filamentous, turf-forming algae. The ability of encrusting corallines to monopolize and retain space without overgrowth depended on the presence of shade (positive effect) if sediment deposition was below that observed on coast characterized by high rates of sedimentation (negative effect). In contrast, the growth and persistence of articulated corallines depended on the absence of shade (negative effect) and high levels of sediment accumulation observed on human-dominated coast (positive effect). The recruitment of filamentous-turfs was facilitated by full light, but was not strongly affected by sedimentation. Instead, filamentous - turfs tolerated heavy sediment accumulation, a factor thought to explain the concomitant increase in spatial dominance of algal-turfs and loss of canopy-forming algae on reefs with heavy sedimentation. Importantly, different habitats will assemble or be maintained to match the environmental conditions in which they are most extensive, demonstrating the key role of physical factors associated with habitat-formers (kelp forests) and human-dominated coast (heavy sedimentation). These results also demonstrate that an appreciation of the integrated roles of physical processes may assist the development of predictive models about the assembly and maintenance of heterogeneity of natural communities, and their potential disruption by humans.
Describes the physical environment of shallow subtidal rocky habitats in temperate coastal areas dominated by large brown algae in the orders Laminariales (the true kelps) and Fucales. Brief comments are made on productivity, especially of Macrocystis and Laminaria populations. Population dynamics and life history are reviewed, and the dynamics of patches (kelp forests characterised by guilds with different canopy adaptations) are reported, with particular reference to stability and adaptive tactics. Dispersal is seen as the most important feature integrating population dynamics, life history and patch dynamics. The consequences of grazing on kelp are indicated, noting different suites of herbivores at different life history stages. Temporal and spatial variability are noted. Disruption and recovery of kelp communities are described. Biogeographical patterns are shown, with convergence to 5 canopy guilds demonstrated. Examples are mainly drawn from the kelp forests of the NE Pacific coastline. -P.J.Jarvis
Understanding the relationship between variation in biodiversity and the alteration of ecosystem processes and stability has become a central ecological issue during the last decade. A large number of experimental and theoretical studies have focused on the effects of changes in spe- cies richness and identity, while the role of variation in species abundance has received less attention in biodiversity experiments. By using an experimental design that effectively separates the effects of species richness and identity, while controlling for variation in species abundance, we examined the consequences of loss of 2 habitat-forming species (the canopy alga Cystoseira compressa and the mussel Mytilus galloprovincialis) in Mediterranean low-shore assemblages of algae and inverte- brates. Results revealed significant effects associated with changes in number and identity of habitat- forming species on other organisms. The magnitude and direction of these effects, however, changed as a function of the abundance of manipulated species. Our findings indicate how changes in biodi- versity of even 2 species can result in complex effects, stressing the importance of investigating non- random loss of habitat-forming species and the need to consider density-dependent effects in biodi- versity experiments, particularly when experiments are undertaken in systems like rocky shores, where density-dependent effects are pervasive.
Kelp forests are phyletically diverse, structurally complex and highly productive components of cold-water rocky marine coastlines. This paper reviews the conditions in which kelp forests develop globally and where, why and at what rate they become deforested. The ecology and long archaeological history of kelp forests are examined through case studies from southern California, the Aleutian Islands and the western North Atlantic, well-studied locations that represent the widest possible range in kelp forest biodi-versity. Global distribution of kelp forests is physiologically constrained by light at high latitudes and by nutrients, warm temperatures and other macrophytes at low latitudes. Within mid-latitude belts (roughly 40–60° latitude in both hemispheres) well-developed kelp forests are most threatened by herbivory, usually from sea urchins. Overfishing and extirpation of highly valued vertebrate apex predators often triggered herbivore population increases, leading to widespread kelp deforestation. Such deforestations have the most profound and lasting impacts on species-depauperate systems, such as those in Alaska and the western North Atlantic. Globally urchin-induced deforestation has been increasing over the past 2–3 decades. Continued fishing down of coastal food webs has resulted in shifting harvesting targets from apex predators to their invertebrate prey, including kelp-grazing herbivores. The recent global expansion of sea urchin harvesting has led to the wide-spread extirpation of this herbivore, and kelp forests have returned in some locations but, for the first time, these forests are devoid of vertebrate apex predators. In the western North Atlantic, large predatory crabs have recently filled this void and they have become the new apex predator in this system. Similar shifts from fish-to crab-dominance may have occurred in coastal zones of the United Kingdom and Japan, where large predatory finfish were extirpated long ago. Three North American case studies of kelp forests were examined to determine their long history with humans and project the status of future kelp forests to the year 2025. Fishing impacts on kelp forest systems have been both profound and much longer in duration than previously thought. Archaeological data suggest that coastal peoples exploited kelp forest organisms for thousands of years, occasionally resulting in localized losses of apex predators, outbreaks of sea urchin popu-lations and probably small-scale deforestation. Over the past two centuries, commercial exploitation for export led to the extirpation of sea urchin predators, such as the sea otter in the North Pacific and predatory fishes like the cod in the North Atlantic. The large-scale removal of predators for export markets increased sea urchin abundances and promoted the decline of kelp forests over vast areas. Despite southern California having one of the longest known associations with coastal kelp forests, widespread deforestation is rare. It is possible that functional redundancies among predators and herbivores make this most diverse system most stable. Such biodiverse kelp forests may also resist invasion from non-native species. In the species-depauperate western North Atlantic, introduced algal competitors carpet the benthos and threaten future kelp dominance. There, other non-native herbivores and predators have become established and dominant components of this system. Climate changes have had measurable impacts on kelp forest ecosystems and efforts to control the emission of greenhouse gasses should be a global priority. However, overfishing appears to be the greatest manageable threat to kelp forest ecosystems over the 2025 time horizon. Management should focus on minimizing fishing impacts and restoring popu-lations of functionally important species in these systems.
Competitive and facilitative interactions are common throughout the rocky subtidal and
may be important when determining organism distribution and abundance. In this study, we used the
corallimorpharian Corynactis californica to examine these relationships as they develop spatially and
temporally between 2 kelp forest habitats. Sampling along Santa Catalina Island, California, USA,
demonstrated that C. californica densities are up to 4-fold greater under canopies of the stipitate kelp
Eisenia arborea than in areas just outside the canopy. Stipitate kelp canopies can act as foundation
species by modifying critical resources (e.g. light and flow) that mediate understory assemblages. It
was determined that the understory algal community is 17% less dense and is distinguished by
branching red algae, whereas the non-shaded community is characterized by dense stands of foliose
and decumbent brown algae. This study quantified the relationship among benthic macroalgae and
C. californica to determine whether macroalgae were negatively or positively affecting C. californica
distributions. Permanent 25 × 25 cm quadrats were established in both the canopy and open habitat,
and understory algal biomass was manipulated with 3 treatments: (1) 100% removal; (2) thinning by
50%; and (3) no removal (control). All treatments were censused and maintained monthly for 1 yr.
C. californica abundance increased in the control treatments in both habitats, and to the greatest
extent under E. arborea canopies, suggesting a positive interaction between understory macroalgae
and C. californica. The results of this study indicate that E. arborea creates a unique habitat that differs
in water flow, light attenuation, and in composition and density of macroalgae. The combination
of these factors under the E. arborea canopy may support large aggregations of C. californica (up to
3200 m–2) in an otherwise sub-optimal habitat compared to subtidal vertical walls.
1] Macrocystis pyrifera (Giant Kelp) forests form important habitats in temperate coastal regions. Hydrodynamics control the transport of nutrients, food particles, larvae and spores at scales ranging from boundary layers around individual blades to entire kelp forests. Our measurements include vertical profiles of current and temperature, and concurrent wave measurements, at a number of different locations in and around a kelp forest at Santa Cruz, California. We find that flow at the site is dominated by variations at diurnal and semidiurnal frequencies. A vertically sheared across-shore flow, consistent with flow driven by an across-shore density gradient, is thought to be important for exchange between the kelp forest and the surrounding coastal ocean. Within the kelp forest, currents are reduced by a factor that correlates with surface canopy coverage, higher frequency internal waves are damped, and onshore transport due to waves (Stokes drift) is estimated to be similar in magnitude to that due to currents. Richardson numbers within the kelp forest are higher than those outside the kelp forest and indicate that the water column within the kelp forest is usually stable to turbulence generation by mean velocity shear., A field investigation into the effects of a kelp forest (Macrocystis pyrifera) on coastal hydrodynamics and transport, J. Geophys. Res., 112, C02016, doi:10.1029/2005JC003430.
Although there is extensive information concerning the colonization sequences of benthic communities, little is known about the successional development of subtidal hard-bottom habitats in highly productive coastal upwelling areas. In these systems, succession is predicted to be fast due to high growth rate of the later dominant colonizers. Using artificial hard substrata a field experiment was conducted in a rocky subtidal area off Northern Chile (Humboldt Current System) and monitored at 3-month intervals to test the following hypotheses: (i) epibenthic succession may proceed through consecutive replacement of species, (ii) there is a fast convergence rate towards natural communities, and (iii) different seasonal starting points for the colonization will produce different community structure over a 1-year period of exposure. Panels were installed on a vertical wall at 17 m water depth. Three replicate panels were sampled every 3 months over a period of 27 months. As a reference, six haphazardly selected plots from the surrounding natural community were surveyed at each sampling date. To evaluate how seasonally varying substratum availability affects community development, further panels were exposed for a 12-month period, starting in four different seasons (n = 3 replicates per season). Community succession was slow and occurred through progressive changes, between early encrusting red corallines, middle Balanus flosculus and late Lagenicella variabilis. After 27 months, the community composition, but not its structure, was similar between experimental and reference communities on surrounding rocky bottoms. Seasonality had no effects and after 1 year of exposure the experimental communities converged towards a common structure. This study indicates that succession of subtidal epibenthic communities follows a slow and predictable pattern with a dominant late colonial species. In addition, aseasonal variability might be more relevant during colonization and succession in this upwelling ecosystem.
This is the first study on the south eastern Pacific coast of South America which details long term, interannual variability in the structure of subtidal rocky-bottom kelp-dominated communities before, during, and after the El Niño Southern Oscillation (ENSO) event of 1997–1998 in northern Chile (23°S). The temporal patterns of the main components of these ecosystems, which included Macrocystis integrifolia, Lessonia trabeculata, echinoids and asteroids, were evaluated seasonally between 1996 and 2004. M. integrifolia demonstrated high interannual variability in temporal patterns of abundance. The 1997–1998 ENSO did not significantly modify the temporal patterns of Macrocystis, although local extinction of M. integrifolia beds occurred during negative thermal anomalies in 1999–2000 (La Niña event), facilitating the establishment of urchin dominated “barren grounds”. The abundance of Lessonia trabeculata showed little temporal variability, and this species dominated the deeper regions of the kelp assemblage (8–13m depth).
Macrocystis integrifolia and Lessonia trabeculata form vast kelp beds providing a three-dimensional habitat for a diverse invertebrate and fish fauna off northern Chile. Habitat
modifications caused by the El Niño Southern Oscillation (ENSO) are likely to alter the inhabiting communities. The aim of
this study was to reveal relationships between distinct habitat structures of a M. integrifolia kelp bed, a dense L. trabeculata kelp bed and L. trabeculata patches colonizing a barren ground, and the associated dominant macrobenthic key species. Seasonally 15 sampling units (10m2 each) of any of the three habitats were monitored by SCUBA divers, which counted sporophytes and macroinvertebrates living
between the latter. Furthermore, samples of plants were analysed in the laboratory to measure the morphological variables:
total plant length, maximal holdfast diameter, stipe number, number of dichotomies per stipe, frond width and total drained
wet mass. Multivariate analysis showed that the L. trabeculata kelp bed is denser, with a higher number of dichotomies per stipe, whereas sporophytes of M. integrifolia are longer with more stipes and wider fronds. Sporophytes of L. trabeculata patchily present on barren ground are shorter and have more stipes compared with those in the dense L. trabeculata kelp bed. Thus, the habitats provide different three-dimensional structures. The associated macrobenthic communities show
a variable degree of overlapping; however, key faunal assemblages were distinguished for each habitat. Our study provides
evidence that habitat diversity drives species diversity, the more homogeneous, monospecifically composed kelp bed habitats
show comparatively low diversity, mainly caused by the dominance of the ascidian P. chilensis and T. tridentata in the M. integrifolia bed, and the mussel A. ater only present in the L. trabeculata bed. Species richness and diversity is highest in the heterogeneous habitat where L. trabeculata patches interrupt the barren ground. Our study revealed morphological differences between M. integrifolia and L. trabeculata kelp beds reflected in stipe number, plant length, dichotomies per stipe, and wet mass, which influence the composition of
the associated characteristic fauna and its functional relations i.e. T. niger and T. tridentata.
Despite their ecological and economic importance, no summary of kelp global biogeography has been produced for almost two
decades. The circumscription of the order Laminariales and familial and generic relationships in the group have changed considerably
recently, in the light of molecular data. A global summary and geographical analysis of kelp species and their distributions
(112 species in 33 genera) is presented. These data are analysed and discussed from the perspective of the new consensus of
relationships within the group, and likely evolutionary events. The putative ancestors of the kelps occur and are overwhelmingly
most diverse, in the cooler waters of northern Japan. The biogeographical evidence suggests three main lines of subsequent
evolution: (a) a diversification producing the four ‘derived’ families Alariaceae, Costariceae, Laminariaceae, and Lessoniaceae
and most extant genera in the temperate northern Pacific, probably during the Miocene. (b) The evolution of an Arctic flora
which invaded the North Atlantic following the opening of the Bering Strait ca. 5.5Ma. (c) At least four separate crossings,
by different genera, of tropical regions from Northern to Southern Hemisphere (and one in the opposite direction). The recorded
impacts of man on these distributions have thus far been minimal, with the notable exceptions of Undaria pinnatifida and species of Saccharina (grown in aquaculture systems for human food). Most genera are monospecific, with many confined to either the western or
eastern temperate North Pacific, whereas the distribution of the most species-rich genera (Alaria, Laminaria, Saccharina) includes the Arctic, and they are widespread in the North Atlantic. This rapid species-level evolution is hypothesised to
have been promoted by the relatively recent invasion of the Atlantic by these taxa. The crossing of the tropics has occurred
in warm-temperate species some of which occur and are sometimes abundant, in deeper water in today’s tropics, refuting the
widespread view that kelps are only present in cold-water habitats. Most of these Southern Hemisphere kelps are in the family
Lessoniaceae, including the only genus not present in the Northern Hemisphere, Lessonia. The origins of this genus are unclear. Knowledge of the phylogeography of the Ecklonia/Eisenia complex is particularly important in understanding Southern Hemisphere kelp biogeography. A number of groups are undergoing
active speciation and, with the lack of a consistent species concept, the species-level taxonomy of the group remains to be
clarified. There is a great need for molecular phylogeographical studies to provide evidence for many of the hypotheses presented
here based on distributional evidence and the currently accepted taxonomic framework.
KeywordsKelps-Global distribution-Evolution-Diversity-Dispersal-Laminariales
Despite the great interest in characterizing the functional structure and resilience of functional groups in natural communities, few studies have examined in which way the roles and relationships of coexisting species change during community succession, a fundamental and natural process that follows the release of new resources in terrestrial and aquatic ecosystems. Variation in algal traits that characterize different phases and stages of community succession on rocky shores are likely to influence the magnitude, direction of effects, and the level of redundancy and complementarity in the diverse assemblage of herbivores. Two separate field experiments were conducted to quantify per capita and population effects and the functional relationship (i.e., redundancy or complementarity) of four herbivore species found in central Chile during early and late algal succession. The first experiment examined grazer effects on the colonization and establishment of early-succession algal species. The second experiment examined effects on the late-successional, dominant corticated alga Mazzaella laminarioides. Complementary laboratory experiments with all species and under natural environmental conditions allowed us to further characterize the collective effects of these species. We found that, during early community succession, all herbivore species had similar effects on the ephemeral algae, ulvoids, but only during the phase of colonization. Once these algae were established, only a subset of the species was able to control their abundance. During late succession, only the keyhole limpet Fissurella crassa could control corticated Mazzaella. The functional relationships among these species changed dramatically from redundant effects on ephemeral algae during early colonization, to a more complementary role on established early-successional algae, to a dominant (i.e., keystone) effect on late succession. This study highlights that functional relationship within consumer assemblages can vary at different phases and times of community succession. Differentiation in herbivore roles emphasizes the need to evaluate consumer's impacts through different times of community succession, and through experimental manipulations to make even broad predictions about the resilience or vulnerability of diverse intertidal assemblages to human disturbances.
We determined whether temporal variation and succession were similar among sites with similar species composition by sampling unmanipulated and cleared plots in a high intertidal assemblage dominated by Endocladia muricata and Mastocarpus papillatus. Sampling was done for 6 years at six sites spanning over 4° of latitude in California. Ten 1×2-m permanent plots were chosen in the central portion of the assemblage at each site. Four of these served as unmanipulated controls, three were cleared (scraped and burned) in the spring of 1985, and three were cleared in the fall of 1985. The cover of sessile and density of motile species were determined by subsampling within the plots from 1985 until 1991. Recovery of the clearings was determined by their similarity to the controls. The algae E. muricata, M. papillatus, and Fucus gardneri, and the barnacle Balanus glandula, were the most abundant sessile organisms in the control plots, although the latter never exceeded 12% cover at any site. The grazing gastropods Littorina scutulata/plena, various limpets, and Tegula funebralis were the most common mobile organisms. The species composition of the common species remained constant in the control plots over the study period and there were few large changes in relative abundance. Significant seasonal variation was detected in 11 species but variation was commonly site-specific.
Many landscapes are characterized by a mosaic of patches in various stages of succession. Whether successional paths dampen, track, or magnify extrinsic variation in initial conditions influences how much historical and site-specific detail is required to explain variation in patch composition. I investigated the patterns and importance of historical effects in a successional marine rocky intertidal community on the central coast of Oregon, USA Patches in the mid-intertidal mussel bed (M. californianus) were manually cleared in a way that mimicked natural disturbances. In four separate blocks (large patches ~9 m2), three sets of plots were initiated with their starting dates staggered by one year. Within each set of plots, I manipulated the presence/absence of two groups of early successional sessile species under each of three predator densities. This design allowed me to address the following general questions: (1) What are the separate and interactive effects of successional age, yearly variation, and initial conditions on the temporal changes observed after disturbance? (2) When do interactions between early species act to dampen or magnify natural variation between years or starting dates? Succession in mid-intertidal patches in the mussel bed displayed complex patterns of historical effects, which varied among species and between different stages of succession. Embedded in this potential complexity were some consistent and repeatable successional trends. Some potentially important canalizing, or 'noise-dampening' forces in this system included: (1) physiological and/or life history trade-offs between dispersal ability and competitive ability, (2) strong direct biotic interactions, which buffer environmental variability, and (3) compensatory ('buffering') responses of species within an important functional group. 'Noise-amplifying' forces included: (1) variable indirect effects of predators, (2) prey size escapes, and (3) predator saturation (or prey 'Swamp' escapes). Understanding the patterns and causes of consistency or contingency in succession will be critical for managing variability in landscapes that are increasingly dominated by anthropogenic disturbance regimes.
Seascapes are the marine analog of terrestrial landscapes, and their importance for ecological processes in marine ecosystems is generally poorly known. This is especially true for giant kelp (Macrocystis pyrifera) forests for which the acquisition of high resolution acoustic terrain data is problematic due to canopy cover. The goal of this study was to determine the effects of geologically forced seascape structure on algal patch structure, and to address the potential for seascape pattern to affect higher order ecological processes within giant kelp forests. The difficulty of terrain data acquisition within giant kelp forests was overcome using a narrow single beam sonar system and the development of processing algorithms that resulted in high resolution (10 m) models of bathymetry and algal patch structure. Algal patch structure was determined for the canopy kelps Macrocystis pyrifera and Pelagophycus porra, and pooled understory algal species. The analysis also enabled estimation of the spatial distribution of a large (> 2 ha) persistent sea urchin barrens. The results highlight the importance of bottom topography and bottom depth distributions on algal distributions, algal patch structure, and the dynamics of the sea urchin barren. Large scale topographic features (ca. 500 m), depth, and their interaction are significantly related to canopy and understory distributions among the forests and known patterns of algal resiliency and persistence. Canopy is preferentially distributed toward large scale topographic highs, whereas understory is preferentially distributed towards topographic lows. Pelagophycus porra, however, does not exhibit a distributional preference among hard bottom topographic features. Large scale topography clearly controls algal patch structure. Greater algal patch density and complexity are associated with topographic highs and lows, whereas patches in planar areas exhibit large core areas with less edge habitat and less interspersion with different canopy guilds. Comparisons of the joint probability distributions of bottom and algal depth distributions among forests indicates that density dependent positive feedback processes potentially reinforce the predominance of their differential canopy guild composition. Seascape structure (1) controls and interacts with algal patch structure to define edge habitat structure and potentially foraging and migration pathways, and (2) defines the margins of the large persistent sea urchin barrens and likely the dynamics of sea urchin feeding and movement. The results reinforce the need for adequate sampling design and replication for probability based benthic assessments when high resolution habitat structure is not available, or the utilization of model based purposive sampling strategies when habitats are known.
Biogenic substrata such as epibenthic mussel aggregations are common in coastal regions worldwide and harbour diverse assemblages of sessile and mobile species. However, colonisation patterns on biogenic substrata are still not well understood. We tested whether succession develops as a linear sequence of temporal changes in the species richness and community structure of sessile and mobile assemblages associated with intertidal mussel beds of sedimentary and rocky shores in Germany and Chile, respectively. Because of their broad differences, these study sites were analysed separately to examine whether similar successional patterns occur under differing environmental conditions and species pools. At each study site, we conducted an experiment that separates the effects of successional age (deployment duration) and the time when settlement substrata are deployed (deployment timing). Colonisation dynamics differed between timings and between sessile and mobile species. In addition, timing effects were stronger at the sedimentary than at the rocky study site. For sessile organisms, for example, species richness increased steadily with successional age at both study sites, but at the sedimentary site, the magnitude of this increase varied between the different months of deployment. For mobile organisms, a high proportion of the total species pool colonised the settlement substrata within the first month of deployment at both sites. After this initial colonization peak, mobile species richness showed a minor but significant increase with successional age at both sites. We suggest that species dispersal ability at the local scale (mobility) mediates the response of species-rich assemblages to natural and anthropogenic disturbances.
The subtidal (10—15 m) assemblage in the relatively sheltered giant kelp forest at Stillwater Cove in Carmel Bay, California, consists of perennial species forming three major vertical layers: a Macrocystis pyrifera surface canopy, a dense subsurface canopy of another kelp, Pterygophora californica, and an understory of articulated and encrusting coralline algae. The kelp canopies alone or in combination can reduce bottom light to <30% (usually <1%) of surface influx. The effects of light reduction by these vegetation layers on algal recruitment and subsequent growth were determined by removing various combinations of canopies over a 2—yr period, and following subsequent changes relative to appropriate controls. Removing both M. pyrifera and P. californica canopies resulted in moderate recruitment of these species as well as of the annual brown alga Desmarestia ligulata var. ligulata. None of these algae recruited into control areas where one or both canopies were left intact. Highest brown and red algal recruitment occurred when both kelp canopies plus understory coralline branches were removed. Removal of the latter alone had no significant effect. The time of year when algal canopies were removed had little effect on the composition of subsequent algal colonization, as the recruitment of noncalcareous species occurred primarily during a short period in the spring. These results indicate that the relatively low levels of both physical and biological disturbance in Stillwater Cove allow the establishment of a few perennial algal species that inhibit their own recruitment, as well as invasion of other species, by shading. This contrasts with nearby kelp forests subjected to greater and more frequent disturbance, and characterized by a diverse assemblage of annual algal species.
The ability of sea urchins to destroy kelp forests, leaving large areas stripped of vegetation and covered by sparse calcareous algae is well known. The reduction in active predators of sea urchins combined with their broad diet makes them an important factor in the structuring of subtidal benthic marine systems. In central and northern Chile, the sea urchin Tetrapygus niger is known to reduce the spread of the subtidal kelp Lessonia trabeculata. However, its impact on the different development stages of L. trabeculata has never been quantified or compared to other possible causes of the loss of material. The objective of this study was to quantify the grazing impact of T. niger on L. trabeculata at different stages of development (recruits, juveniles and adults). An exclusion experiment was conducted to evaluate the grazing effect of T. niger on kelp recruitment within a kelp bed, and kelp transplant experiments were conducted to quantify T. niger's impact on the stipes and fronds of juvenile and adult L. trabeculata. Our results showed that under natural sea urchin densities (10 ind. m− 2), T. niger prevented the recruitment of L. trabeculata. Tetrapygus niger completely consumed juvenile plants but only attacked the stipes of adult plants. Tetrapygus niger seems to use different feeding strategies depending on the ontogeny of the plant. Lessonia trabeculata seems unable to defend itself against the impact of intensive grazing by sea urchins, which may be the primary source of mortality of recruits and juveniles of L. trabeculata. However, T. niger's impact on adult plants is limited and shared with other herbivores that graze the fronds, such as fishes and spider crabs.
Evidence is presented which indicates the importance of historical events in determining the structure of a variety of natural communities. In the fouling community at Beaufort, North Carolina, the order of larval recruitment determined which species monopolized the available space during initial community development. In other systems, community structure could be explained only by referring to the specific historical events which determined the presence or absence of important consumers. Since history was relevant to the observed community structure, multiple stable points are an undeniable reality in space and time in these systems.
Patterns of benthic colonization and succession were investigated on a temperate rocky cliff (Aegean Sea, Eastern Mediterranean). Cement and ceramic panels deployed on the rocky substratum at 25–30m depth were sampled every 3months over a 2-year period yielding 28 floral and 156 animal species. Diversity, cover and abundance had low values at short immersion periods and increased at the long ones. The vagile fauna responded to the increasing habitat complexity offered by the development of algal turfs and sessile species, and the community structure remained highly dynamic. Unlike the duration of immersion, the type of substratum didn't affect species colonization except for decapods that showed a preference for cement panels. Three to four stages of succession were recorded over immersion periods, according to vagile and sessile biota, respectively, during which species richness and abundance increased. The structure of the developed communities on both artificial materials differed from the natural algal-dominated benthic community of the same area, suggesting that the recovery of rocky shore communities on temperate cliffs is time consuming.
Colonization and successional development of very diverse subtidal assemblages on rocky surfaces are not clearly understood. Artificial units of habitat (AUHs) made of nylon pot-scourers were used to test predictions from various models of succession. An experiment was designed in an attempt to unconfound the period of deployment (equals age of succession) from the time-period during which AUHs were deployed. AUHs were deployed in two sites, 100 m apart, for 1 month, starting at 0, 1, 2 and 3 months, for 2 months, starting 0 and 2 months and for 4 months from 0 month. Ninety-nine taxa were recorded in the AUHs. Successional change was not due to nett accumulation of taxa, nor simply to longer-term AUHs sampling successive different periods of time. Assemblages developing over the same period were different, but only a small amount of the variability was seasonal. Assemblages converged as period of deployment increased. There was less change from one to two months than from two to four months in the development of assemblages, but some of this was due to seasonal difference between the first and last two months. There were no differences between sites in any of the analyses of structure of assemblages. Few individual taxa showed consistent patterns of changing abundance with length of deployment. Different types of organisms showed markedly different patterns of arrival. The increase in number of species of gastropods was much smaller than the corresponding increase in number of taxa of polychaetes. Succession in these assemblages is complex and variable, but shows some repeated patterns. Fitting these to models of succession is only partially successful and new models are needed for very diverse assemblages.
The biodiversity of hard-bottom substrata comprises species growing on exposed rock and in hidden microhabitats, such as cracks and crevices. This study examines the succession of epibenthic organisms colonizing an artificial substratum with one surface exposed and one surface hidden on a vertical wall off northern Chile. On each sampling date species coverage of three replicate panels on both surfaces was assessed. The hidden surface was dominated in terms of coverage by the bryozoans Membranipora isabelleana and Lagenicella variabilis, while algae were absent. In contrast, the exposed surface was dominated by encrusting red corallines and the red alga Rhodymenia corallina. At the end of the experimental period both surfaces were dominated by colonial suspension feeders. but showed it different community structure and successional pattern. On the exposed surface, competitive exclusion was identified as an important aspect of succession. whereas on the hidden surface this pattern was not observed. These findings have implications for overall biodiversity. because pioneer species that are not able to survive long periods on exposed surfaces become restricted to hidden surfaces, from where they spread laterally. Thus, hidden microhabitats provide refuges for certain species. and may play an important role in the overall succession on rock faces. We conclude that examination of hidden microhabitats is necessary in order to fully understand succession in hard-bottom habitats.
Propagule dispersal is fundamental in regulating the strength of demographic and genetic interactions between individuals both within and among populations. I studied spatiotemporal variability in propagule (zoospore) supply of a continuously reproducing seaweed, giant kelp Macrocystis pyrifera, to examine: (1) the extent to which local zoospore production is coupled to (correlated with) temporal variability in zoospore supply; and (2) spatial variability in the strength of such coupling. Macrocystis pyrifera planktonic zoospores were quantified from seawater samples pumped on numerous dates in 1999 from just above the substratum at various sites in the Point Loma kelp forest, southern California, USA. Zoospore collections were made at a site in the forest interior approximately three times per month from late February through mid-November. Sample collection overlapped with complete demographic surveys of the local population (100 m super(2)) to determine local reproductive output. Temporal variability in zoospore supply was strongly correlated with relative changes in the density and size structure of local reproductive adult sporophytes; 76% of variability in zoospore supply was explained by local reproductive output. This tight coupling between zoospore supply and local reproduction appeared to be driven by low-displacement, oscillating currents in the forest interior due to the cumulative drag of adult sporophytes, which kept zoospores close to their release site. High coupling between zoospore supply and local reproduction was validated at two additional interior sites separated by 1 km; 78% of variability in zoospore supply was explained by local reproductive output at these sites. Due to lower sporophyte densities, however, the forest edges experienced rapid, unidirectional currents that appeared to transport zoospores far from their release site, effectively decoupling zoospore supply from local reproduction; only 38% of variability in zoospore supply was explained by local reproductive output at these sites. The results suggest that the size of and location within kelp populations is an important determinant of the importance of local reproduction to zoospore supply due to the effects of flow modification by kelp canopies on zoospore dispersal.
Lessonia trabeculata is an important economic and ecological algal resource of Chile. Due to intense use in abalone and alginate industries, severe problems of over-harvesting are emerging. We compared sporophyte-initiation and -growth in two populations from northern and southern Chile (Bahía Inglesa and Maicolpué) under laboratory conditions. Irradiance and temperature were the most important factors affecting gametophyte development. Meiospores harvested in spring exhibited maximum reproductive and growth potential, while spores released during autumn were moribund, and died within a few days. In both study sites, we found evidence for acclimation: Meiospores collected in summer required higher levels of irradiance and temperature for maximum development than winter spores. Juvenile sporophytes from both localities responded similarly to temperature and/or irradiance. The best conditions for recruitment of sporophytes from both localities were 15°C and white fluorescent light of 40–70 μmol m−2 s−1. Although due to its low growth potential L. trabeculata is not a good candidate for mariculture, our results provide the necessary knowledge for laboratory-based seedling production, which is needed for restoration and repopulation projects in damaged areas.
Understanding the mechanisms of ecological succession is fundamental to predict recovery patterns and restore the increasingly disturbed marine habitats; the season in which disturbance occurs severely affects these processes but this factor has not been thoroughly studied in sublittoral cliffs. Thus, seasonal patterns of benthic colonization and succession were investigated on a temperate rocky cliff (Aegean Sea, eastern Mediterranean). Cement panels, seasonally installed on the rocky substratum at 25–30m depth, were sampled every 3months over a 1-year period each, yielding 40 floral and 158 animal species. Diversity, cover and abundance were very low at the initial immersion period and increased toward the late periods. The immersion period and the season of installation had a strong effect on diversity and abundance; decapods showed increased colonization on panels installed in spring, and polychaetes on hibernal panels. The vagile fauna responded to the increasing habitat complexity offered by the development of algal turfs and sessile species. Community structure remained highly dynamic up to the end of the experimental installation and quite different from that of the surrounding benthic community. Two stages of succession, considering vagile and sessile biota, either separately or altogether, were observed over immersion periods; the first was characterized by high variability that can be related to the presence of different colonizers in different seasons, whereas the second, exhibited higher species richness and abundance and showed increased endogenous similarity. Thus, regardless of the season colonization started the developed communities converged toward a common structure, after one year of immersion. An exception was hibernal installation, in which the 12-month immersion period was recognized as a third stage characterized by increased diversity also showing an increased similarity with the adjacent algal community; this suggests that benthic colonization in such environments is faster when succession starts in winter.
Wave-exposed rocky intertidal habitats of central Chile exhibit zonation of algal morphologies rather than strict patterns of species zonation. In low shore areas, there is a vertical sequence of perennial belts of calcareous crusts, kelp-like forms and expanded cushions or non-calcareous crusts. The calcareous crusts are represented by species of Mesophyllum, the kelp-like forms include Lessonia nigrescens and Durvillaea antarctica, while the cushions are represented by Gelidium chilense and G. lingulatum and the noncalcareous, expanded crusts by Codium dimorphum. Thin and thick blades, represented by Iridaea laminarioides, Ulva rigida and Porphyra columbia and filamentous forms including Ceramium rubrum, Centroceras clavulatum and Polysiphonia spp. are more patchy than the lower, perennial belts. They may, however, form distinct temporal monocultures at upper intertidal levels. Upper and lower limits of the various zones are set by interactions of several factors, the relative importance of which can change seasonally. When some of the factors restricting species distribution are experimentally removed, other interactions among factors become limiting.Within each zone, species are morphologically similar, with the abundance of species being regulated by symmetric competitive interactions. Competition is often asymmetric at the boundaries of zones except when adults of small-sized forms interact with morphologically similar juveniles of larger forms. Irrespective of their extremely different morphologies, the permanent, zone-forming algal species generally combine escape from grazers or defensive adaptations with clear competitive abilities. Nevertheless, there is a clear competitive hierarchy which is expressed in vertical displacements and zonation. The lowershore habitats could potentially be occupied by any of the different types of algae. Fast growth and large size allow the kelps to occupy this zone pushing the calcareous crust dominated-zone down into shallow subtidal areas and displacing the cushions and fleshy crusts into the low and middle intertidal regions. In turn, these last forms can displace thick and thin foliose forms and filaments to upper levels on the shore. Displaced forms may exist as patches at various levels of the shore.
Kelp regeneration was observed for the first time in St. Margaret's Bay, Nova Scotia, Canada in an area known to have been devoid of macroalgae for several years. The regeneration was destroyed by sea urchins within 10 months. Experimentally induced kelp regeneration met a similar fate under normal grazing pressure. At the lowest sea urchin biomass and density encountered re-establishment of mature kelp stands seems highly unlikely. The sea urchin population required to suppress kelp regeneration is fed by benthic microalgae. Diatoms and other pioneer algal community species were found in the guts of sea urchins. The mean standing crop of benthic microalgae was found to be, 2.2 g C m-2 and production estimated as ca 15 g C m-2yr-1 at 8m depth. Most of the primary production of St. Margaret's Bay has been lost with the disappearing kelp populations.
Stability properties of the barren state of a kelp forest-sea urchin system were studied in northern Norway. The ability of the sea urchin Strongylocentrotus droebachiensis to maintain high population densities and recover from perturbations, and the succession of kelp forest revegetation, were studied experimentally by reducing the sea urchin density on a barren skerry. Additional information was obtained from community changes following a natural, but patchy, sea urchin mortality that varied between sites. On the barren grounds, high sea urchin densities (30 50 per m2) is maintained by annual recruitment. Severe reductions of sea urchin densities initiated luxuriant kelp growth, while more moderate reductions allowed establishment of opportunistic algae (during spring and early summer), but no kelps. Succession of algal growth, after the severe decline in sea urchin densities, followed a predictable pattern. At first the substrate was colonized by filamentous algae, but within few weeks they were outcompeted by the fast growing kelp Laminaria saccharina. After 3–4 years of the removal experiment, the slower-growing, long-lived kelp L. hyperborea became increasingly dominant. Increased food availability after reduction in sea urchin density led to increased individual growth of the remaining sea urchins. However, the population density did not increase, neither from recruitment nor immigration from adjacent areas with high sea urchin densities. Possibly, early establishment of a dense kelp stand, may represent a breakpoint in the ability of sea urchins to reestablish a barren state. The ability of L. saccharina quickly to invade and monopolize an area may have both positive and negative effects on the succession towards the climax L. hyperborea kelp forest. Competitive interactions may slow the process, but development of a dense stand of L. saccharina will also reduce grazing risk on scattered recruits of the more slowly growing L. hyperborea.
Algal succession within a subtidal forest of the giant kelp Macrocystis pyrifera was studied by following colonization and community development on concrete blocks fastened to the bottom. Sets of blocks were placed in the bed at 3-month intervals. Subsequent algal development on each set was followed for over a year. All macroscopic species attached to the substrata were noted, and the number and lenght of basal branches determined every 1 to 3 months. Colonizing plants fell into 3 categories: rapid-growing ephemerals, and rapid and slow-growing perennials. Ephemerals such as Giffordia (Ectocarpus) mitchellae, Colpomenia peregrina, and diatom films generally produced and initial bloom on the blocks but were gradually replaced by perennials (articulated corallines, Rhodymenia spp., Gigartina spp.) characteristic of the mature kelp community. These stages, rather than representing ecological succession, seemed to reflect differences in growth rate and success in interspecific competition for space and light. Colonization on the blocks varied with season, indicating that most species have either a spring-summer or fall-winter period of maximum reproduction. M. pyrifera sporophyte colonization was greatest in spring. During community development, algal diversity (H), number of species (s) and evenness (J) all reached a peak within 100 to 200 days regardless of the time the blocks were started. Diversity and number of species then fell as ephemeral species disappeared. These species were apparently unable to compete with perennials and, once gone, did not recolonize. Evenness remained high.
The recovery of microbial communities removed from hard substrates was studied in the laboratory and on microepiphyton in
the White Sea, in St. Petersburg, and in Karelija. The removal of these communities from hard substrates destroyed their spatial
structure. Recovery was allowed to proceed from the suspension on a horizontal substrate in stagnant water at low temperature.
The sequence of colonization in the laboratory was the same as that in the field. Laboratory recovery was complete in 12–24
h and did not depend on the age of the natural community. From the comparison between laboratory and field data on such mechanical
disturbance, a pattern of recovery, termed ‘self-assembly’, is proposed.
It has been hypothesized that the high diversity of giant kelp forests is due primarily to the provision of energy and habitat by the giant kelp (Macrocystis pyrifera). In this article, I use a 19-year-long kelp forest-monitoring data set from the Channel Islands National Park (a) to identify associations between subtidal species and forested or deforested habitats, (b) to generate an idealized food web for Southern California giant kelp forests in order to identify the primary conduits of energy flow through the system, and (c) to determine changes in the diversity and complexity of this food web due to localized giant kelp deforestation. A total of 275 common species were observed in the park between 1982 and 2000, of which 36% occurred significantly more often in kelp-forested areas than in deforested areas (that is, sea urchin barrens); 25 species were found exclusively in forested areas. Most of these associations were
clearly identified as trophic and/or structural associations with giant kelp itself. The producer level of the food web was diverse, although giant kelp apparently represents the greatest single source of fixed carbon through either direct grazing or the production of phytodetritus. Primary, secondary and tertiary consumer levels were also represented by numerous species, and generalist consumers were common. With deforestation, the source of primary production shifts from primarily kelps to ephemeral microalgae, macroalgae, and phytoplankton. These results support the reliance of giant kelp forest food-web structure and diversity on the presence of the forest itself.
Deployment of artificial substrata is a common method of investigating early community development and recruitment, but rarely are such experiments of long enough duration to include even year time scales. We placed replicate, machined-slate panels (1515cm) in the intertidal and at depths of 6 and 12m at two sites of differing flow rate at Lough Hyne, SW Ireland. These were serially replaced every 30–60days for a period of 5years (1997–2002), except in the intertidal (2000–2002). The number and identity of all recruits were recorded. Recruitment varied over several orders of magnitude both on temporal and spatial scales. The greatest source of variability was between the intertidal (with few species or recruit numbers) and the subtidal zones (many species, some with thousands of recruits per panel per 30days). Highest levels of recruitment occurred at the low-flow site (Labhra Cliff). Here, recruitment was dominated by the serpulid polychaete, Pomatoceros sp., reaching ~4000individuals per panel per 30days. Highest species richness occurred, however, at the high flow site (Whirlpool Cliff). At this site more colonial forms (e.g. bryozoans) settled. Season was found to be the dominant pattern explaining subtidal recruit and species number variability. Year, however, was the dominant temporal pattern explaining change in diversity (Shannon–Wiener H). In space, depth explained most variability of recruit numbers, whereas site explained more variation in species richness. Both these spatial factors contributed similarly to variability of diversity (H). Recruitment has long been known to vary considerably over large spatial scales, such as with latitude and isolation, but we that show changes of a similar magnitude in recruitment can occur across small spatial scales. Individual taxa showed varied temporal patterns of recruitment including continuous, regular seasonal fluctuations and irregular pulses in particular years.
The effect of four substrata (concrete, plywood, fibreglass and aluminium) on the recruitment of species and development of an intertidal estuarine fouling assemblage was examined in Quibray Bay of Botany Bay, New South Wales, Australia. Many species, including the oyster Saccostrea commercialis (Iredale & Roughley) and the barnacles Hexaminius sp., Balanus amphitrite Darwin and Balanus variegatus Darwin, recruited in greater numbers on concrete or plywood surfaces than on fibreglass or aluminium. As a result, patterns of change in the number of species through time were dependent on the substratum. Multivariate analyses indicated that assemblages on different substrata were significantly different after 1 or 2 months of submersion, but became more similar after longer periods (up to 4–5 months). The reasons for this gradual conformity varied depending on the season of submersion and the composition of the species settling in a particular season.The results of this study indicated that the nature of the substratum can affect both initial colonisation of particular species and the development of the assemblage over time. Because the effect of substratum varies with the period of submersion, comparisons of various studies on fouling assemblages using different natural and artificial substrata and for varying lengths of time are likely to be very difficult.
Photographic and video methods are frequently used to increase the efficiency of coral reef monitoring efforts. The random point count method is commonly used on still images or frame-grabbed video to estimate the community statistics of benthos. A matrix of randomly distributed points is overlaid on an image, and the species or substrate-type lying beneath each point is visually identified. Coral Point Count with Excel extensions (CPCe) is a standalone Visual Basic program which automates, facilitates, and speeds the random point count analysis process. CPCe includes automatic frame-image sequencing, single-click species/substrate labeling, auto-advancement of data point focus, zoom in/out, zoom hold, and specification of random point number, distribution type, and frame border location. Customization options include user-specified coral/substrate codes and data point shape, size, and color. CPCe can also perform image calibration and planar area and length calculation of benthic features. The ability to automatically generate analysis spreadsheets in Microsoft Excel based upon the supplied species/substrate codes is a significant feature. Data from individual frames can be combined to produce both inter- and intra-site comparisons. Spreadsheet contents include header information, statistical parameters of each species/substrate type (relative abundance, mean, standard deviation, standard error) and the calculation of the Shannon–Weaver diversity index for each species. Additional information can be found at http://www.nova.edu/ocean/cpce/.
The effect of substratum complexity on the early stages of colonization by mobile epifauna was assessed through a comparative study based on the architecture of artificial substrata. We conducted field observations over 4 years, on six types of small plastic substrata placed in the low intertidal zone of an exposed rocky shore, for varied immersion periods (1, 2, 4 and 12 wk). The use of artificial substrata allowed us to manipulate independently structural and spatial features of the habitat, such as total area, amount of folds, intercepting area, total volume, and interstitial volume. The invertebrate fauna colonizing over 300 sample units was recorded, and their densities compared as a function of substrata type and immersion time. Microcrustaceans predominated during the initial stages in all substrata. In this category, harpacticoid copepods and amphipods were the most abundant taxa. The effect of the original substratum complexity seemed to be restricted to the early stages of colonization, since after 12 wk of immersion the original geometry was greatly modified by fouling organisms, particularly ascidians and epiphytic algae. The geometric characteristic that most influenced epifaunal composition and density was the substratum folding, a one-dimensional measure that evaluates the amount of filaments and folds in the substratum's surface. Folding was correlated with high faunal densities and high initial colonization rates, and proved to be a better density predictor than total substratum area, or volume. This correlation was especially well defined for amphipods.
Marine ecosystems were among the first to provide potential examples of multiple stable states. However, remarkably few of these have been explored in detail, and none have been rigorously confirmed. This may be because differences between alternative states are too subtle to document in the context of regular disturbance, because one state is naturally far more likely to occur than any other, or because most environments naturally support only one type of stable community. It is also possible that the temporal and spatial criteria required to document alternate stable states rigorously may be too difficult to meet in most circumstances. Nevertheless, the possibility of alternative stable states has recently received renewed attention in the context of marine conservation biology. People may be widening the range of habitats in which alternate stable states are possible, or they may be shifting communities to new domains of attraction that rarely occur in the absence of massive anthropogenic perturbations. The ability of people now to alter ocean ecosystems on global scales may eliminate “edge effects” that might otherwise rescue perturbed communities. Ecosystems with alternate stable states are characterized by positive feedback mechanisms that stabilize transitions; even if return to original conditions is predicted (that is, the alternate states are not stable), the same mechanisms will retard recovery. This may explain in part why return to original conditions following anthropogenic disturbance is slower than expected. Slow recovery times and transitions to new states are both potentially costly to human societies. Thus, from a conservation perspective the indefinite persistence of an alternate state may be less important than the presence of feedback loops that slow recovery. Both possibilities reinforce the arguments for application of the precautionary principle in managing marine ecosystems.
We investigated the process whereby juveniles of the kelp Agarum cribrosum escape grazing by the green sea urchin, Strongylocentrotus droebachiensis, on urchin barrens in the rocky subtidal zone in the Mingan Islands, northern Gulf of St. Lawrence. The highest recruitment of juvenile A. cribrosum occurred under the canopy of the large filamentous phaeophyte Desmarestia viridis, where urchin densities were markedly reduced, compared to the surrounding area. This pattern of distribution appeared to be related to the wave-induced sweeping motion of D. viridis, although currents may modify the back and forth motion of the alga by pushing the canopy towards a specific direction, thereby allowing urchins to invade the non-swept areas. The density of juveniles under D. viridis plants increased with plant size and increasing proximity to the holdfast. Living under D. viridis slightly reduced the growth rate of the A. cribrosum juveniles, but this loss in growth was clearly outweighed by the gain in protection from sea urchin grazing. The time scale over which D. viridis provides protection is in the order of months, as D. viridis is an annual alga that disappears in early autumn. This defensive association of juvenile A. cribrosum with D. viridis is possibly a successional step leading to the formation of mature stands of A. cribrosum.