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Abstract Aim: Topographic complexity is widely accepted as a key driver of biodiversity, but at the patch-scale, complexity–biodiversity relationships may vary spatially and temporally according to the environmental stressors complexity mitigates, and the species richness and identity of potential colonists. Using a manipulative experiment, we assessed spatial variation in patch-scale effects of complexity on intertidal biodiversity. Location: 27 sites within 14 estuaries/bays distributed globally. Time period: 2015–2017. Major taxa studied: Functional groups of algae, sessile and mobile invertebrates. Methods: Concrete tiles of differing complexity (flat; 2.5-cm or 5-cm complex) were affixed at low–high intertidal elevation on coastal defence structures, and the richness and abundance of the colonizing taxa were quantified after 12 months. Results: The patch-scale effects of complexity varied spatially and among functional groups. Complexity had neutral to positive effects on total, invertebrate and algal taxa richness, and invertebrate abundances. However, effects on the abundance of algae ranged from positive to negative, depending on location and functional group. The tidal elevation at which tiles were placed accounted for some variation. The total and invertebrate richness were greater at low or mid than at high intertidal elevations. Latitude was also an important source of spatial variation, with the effects of complexity on total richness and mobile mollusc abundance greatest at lower latitudes, whilst the cover of sessile invertebrates and sessile molluscs responded most strongly to complexity at higher latitudes. Conclusions: After 12 months, patch-scale relationships between biodiversity and habitat complexity were not universally positive. Instead, the relationship varied among functional groups and according to local abiotic and biotic conditions. This result challenges the assumption that effects of complexity on biodiversity are universally positive. The variable effect of complexity has ramifications for community and applied ecology, including eco-engineering and restoration that seek to bolster biodiversity through the addition of complexity.

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... A more detailed description of the characteristics of both artificial and natural habitats can be found in Perkol-Finkel et al. (2012). The study focused on the low-intertidal (≈ 0 to + 20 cm relative to mean low-water level, average tidal amplitude ≈ 30 cm), as this is where most eco-engineering tests are in progress (O'Shaughnessy et al., 2020;Strain et al., 2021). ...
... Increasing surface topographic complexity generally has positive effects on biodiversity in both natural and artificial habitats (Stein et al., 2014;Loke and Todd, 2016;Strain et al., 2021). These effects are related to both increased surface area and supply of microhabitats which can differ in light, temperature, humidity and predation access (Strain et al., 2018a). ...
... These effects are related to both increased surface area and supply of microhabitats which can differ in light, temperature, humidity and predation access (Strain et al., 2018a). A recent meta-analysis of eco-engineered surfaces (Strain et al., 2018b) and a global experiment (Strain et al., 2021) have both highlighted, however, that the outcomes of topographic enhancements can be extremely variable among locations, tidal levels, latitudes and studies, warning about generalizations. Our results raise additional questions about the generalized benefits provided by topographic enhancements of artificial surfaces, as this may not always reproduce relevant natural features. ...
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Marine infrastructures are increasing, generating a variety of impacts and introducing artificial habitats which have low ecological value and support assemblages that differ significantly from those on natural rocky coasts. While in the past there was little ecological consideration as to how artificial structures were built, now the trend is to look for “greener” designs inspired by or mimicking nature. These greening efforts have had a strong focus on enhancing physical habitat structure to support more diverse assemblages, driven by the untested assumption that artificial habitats lack the physical structure proper to natural habitats. We tested this assumption by comparing five descriptors of physical structure (inclination; exposure; roughness; abundance, and diversity of surface morphological microelements) across a combination of natural and artificial habitats of regular and irregular morphologies (seawalls = artificial regular; cliffs = natural regular; breakwaters = artificial, irregular; and boulder fields = natural irregular) in the North Adriatic Sea. Most structural descriptors were similar between artificial and natural habitats. Only inclination was consistently steeper in the artificial than in the natural habitats. Other minor differences in roughness or in the abundance of some surface microelements were related to the general morphology (regular or irregular) of the habitat rather than to its artificial or natural identity. The outcomes challenge the widespread assumption that artificial habitats lack the physical structure proper to natural habitats and stimulate renewed consideration about other structural and non-structural elements that could enhance the performance and sustainability of artificial marine structures, such as construction material, environmental setting or maintenance. They also encourage a wider reflection about what makes an artificial building surface “greener”: structural complexity is an important ecological parameter, and its deliberate increase will lead to responses in the biota, however, this may not necessarily match “more natural” conditions.
... Research and development of habitat creation in coastal environments, however, is decades behind artificial reef research, but has flourished in recent years (for a review see Strain et al., 2017a). IGGI interventions in coastal environments have ranged from the addition of microtexture (Coombes et al., 2015), crevices and grooves (Martins et al., 2010;Borsje et al., 2011) and artificial rock pools (Evans et al., 2016;Firth et al., 2016b) to existing coastal structures, to the use of precast habitat enhancement units and panels (Browne and Chapman, 2014;Perkol-Finkel et al., 2018;Evans et al., 2021;Strain et al., 2021), all yielding promising biodiversity outcomes. Furthermore, habitatforming species such as mussels and oysters , corals (Ng et al., 2015) and canopy-forming algae (Falace et al., 2006;Perkol-Finkel et al., 2012), can be seeded onto artificial structures to encourage settlement of conspecifics and increase biodiversity. ...
... Furthermore, habitatforming species such as mussels and oysters , corals (Ng et al., 2015) and canopy-forming algae (Falace et al., 2006;Perkol-Finkel et al., 2012), can be seeded onto artificial structures to encourage settlement of conspecifics and increase biodiversity. Still, the majority of IGGI trials have been small-scale, focused on either offshore artificial reefs or coastal intertidal habitats, confined to mostly temperate and occasionally subtropical climates (Strain et al., 2017a), and with few comparisons made among geographic or environmental contexts (but see Hsiung et al., 2020;Strain et al., 2021;Clifton et al., in review). Despite the likely context-dependency of interventions, government agencies and planning authorities are increasingly recommending and implementing integrated greengray infrastructure strategies as mitigation and compensation for environmental damage caused by new developments (e.g., 'Biodiversity Net Gain'; Dafforn et al., 2015b;Naylor et al., 2017;Evans et al., 2019). ...
... The only finding that agreed with our hypotheses was that recruited mussels were bigger on the biologically complex tiles that were seeded compared to those that recruited to unseeded tiles. This study replicated methods used by previous intertidal experiments in locations across the globe, including Plymouth and Tel Aviv (Strain et al., 2021). In Plymouth, we found similar effects of physical complexity in the subtidal zone as previously found in the intertidal (Strain et al., 2021), with physical complexity having no detectable influence on taxon richness in either instance. ...
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In response to the environmental damage caused by urbanization, Nature-based Solutions (NbS) are being implemented to enhance biodiversity and ecosystem processes with mutual benefits for society and nature. Although the field of NbS is flourishing, experiments in different geographic locations and environmental contexts have produced variable results, with knowledge particularly lacking for the subtidal zone. This study tested the effects of physical complexity on colonizing communities in subtidal habitats in two urban locations: (1) Plymouth, United Kingdom (northeast Atlantic) and (2) Tel Aviv, Israel (eastern Mediterranean) for 15- and 12-months, respectively. At each location, physical complexity was manipulated using experimental tiles that were either flat or had 2.5 or 5.0 cm ridges. In Plymouth, biological complexity was also manipulated through seeding tiles with habitat-forming mussels. The effects of the manipulations on taxon and functional richness, and community composition were assessed at both locations, and in Plymouth the survival and size of seeded mussels and abundance and size of recruited mussels were also assessed. Effects of physical complexity differed between locations. Physical complexity did not influence richness or community composition in Plymouth, while in Tel Aviv, there were effects of complexity on community composition. In Plymouth, effects of biological complexity were found with mussel seeding reducing taxon richness, supporting larger recruited mussels, and influencing community composition. Our results suggest that outcomes of NbS experiments are context-dependent and highlight the risk of extrapolating the findings outside of the context in which they were tested.
... The (comparatively) smooth surfaces of oil and gas infrastructure may alter the species composition. Increased habitat complexity (3-D relief of a surface) generally increases the biodiversity and abundance of marine fouling communities (Strain et al., 2021), with platform complexity linked to enhanced diversity and abundance of fishes (e.g., Meyer-Gutbrod et al., 2019a). The smooth surfaces of oil and gas infrastructure may also alter the species composition of invertebrate communities, especially when they are "new" and the ecological succession process is just commencing (Sommer et al., 2019). ...
... Toxic responses may cause change in benthic species composition, either through outright mortality, or changes to reproduction, feeding, or other physiological parameters that impact an organism's fitness (Hook et al., 2014). Higher concentrations of environmental contaminants have been associated with increased proportions of invasive species, which frequently have higher tolerance of environmental contaminants (reviewed in Strain et al., 2021). The presence of offshore oil platforms has been shown to change benthic communities in the North Sea and the Gulf of Mexico, both as a result of increased production and enrichment of organic matter, as well as the elevations in environmental contaminants and changes in sediment size around oil platforms (Montagna and Harper, 1996;Henry et al., 2017). ...
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When offshore oil and gas infrastructure is no longer needed, it is either removed, partially removed, left in place, or left in place but repurposed. These processes are collectively referred to as decommissioning. Australian legislation requires oil and gas companies to develop acceptable plans for the safe removal of all offshore infrastructure at the end of a project’s life. Over the next 50 years, the liability for this decommissioning in Australia is expected to exceed US$45 billion. Unlike countries such as Norway, the United Kingdom and the Netherlands, Australian decommissioning activities are in their infancy, with only three cases (to date) in Commonwealth waters where infrastructure has been left in place or partially removed as part of decommissioning. Differences between the Australian marine environment and that of other regions around the world where decommissioning-related research is better progressed include very low sedimentation rates, both tropical and temperate habitats, different species composition, low primary production, and frequent tropical cyclones, as well as unique sociodemographic and cultural characteristics. Accordingly, the outcomes of the decision support tools used in other regions to identify preferred decommissioning options may not be equally applicable in Australia. Here we describe research to support risk and impact assessment for offshore decommissioning in Australia, where full removal of infrastructure is the “base case” regulatory default, but other options including partial removal and/or repurposing might provide similar or better outcomes when environmental, social, economic and seafood safety aspects are considered. Based on our review we propose an integrated framework for research needs to meet legislative requirements for decommissioning and identify research gaps that need to be addressed to inform decision-making for decommissioning in the Australian context.
... These results contradicted with the outcomes of Vozzo et al. (2021) and Strain et al. (2020) where the addition of complexity, and surface area through habitat structure and seeding increased species richness and diversity of sessile taxa in Sydney. Conversely, Strain et al. (2021) found negative or no effects of adding physical complexity and surface area on diversity of sessile taxa in 3 locations, across the globe (see also O'Shaughnessy et al., 2021 which was conducted in the subtidal). This suggests that the effects of complexity on the diversity of colonising organisms is context dependent and varies between locations. ...
... In the global study carried out by Strain et al. (2021), the addition of physical complexity consistently enhanced sessile invertebrate species richness in most (11 out of 14 locations) of the study sites regardless of their regional climates. However, our study in Penang showed no differences in the species richness of sessile organisms between complex and flat tiles. ...
Article
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Increasing human population, urbanisation, and climate change have resulted in the proliferation of hard coastal infrastructure such as seawalls and breakwaters. There is increasing impetus to create multifunctional coastal defence structures with the primary function of protecting people and property in addition to providing habitat for marine organisms through eco-engineering - a nature-based solutions approach. In this study, the independent and synergistic effects of physical complexity and seeding with native oysters in promoting diversity and abundances of sessile organisms were assessed at two locations on Penang Island, Malaysia. Concrete tiles with varying physical and biological complexity (flat, 2.5 cm ridges and crevices, and 5 cm ridges and crevices that were seeded or unseeded with oysters) were deployed and monitored over 12 months. The survival of the seeded oysters was not correlated with physical complexity. The addition of physical and biological complexity interacted to promote distinct community assemblages, but did not consistently increase the richness, diversity, or abundances of sessile organisms through time. These results indicate that complexity, whether physical or biological, is only one of many influences on biodiversity on coastal infrastructure. Eco-engineering interventions that have been reported to be effective in other regions may not work as effectively in others due to the highly dynamic conditions in coastal environment. Thus, it is important that other factors such as the local species pools, environmental setting (e.g., wave action), biological factors (e.g., predators), and anthropogenic stressors (e.g., pollution) should also be considered when designing habitat enhancements. Such factors acting individually or synergistically could potentially affect the outcomes of any planned eco-engineering interventions.
... Results of our global mechanistic experiments support many observational studies documenting positive relationships between heterogeneity and biodiversity but contrast a few studies that have shown unimodal or negative relationships for individual taxa or trophic groups 7,10-14,74 . Unimodal and negative relationships have been explained by specific combinations of habitat compositions and configurations, and animal nichebreadth and dispersal traits 15,74 . We probably found positive relationships because our heterogeneity tests were based on short binary treatments (instead of long continuous gradients 11 ), dispersal is less limiting in small-scale facilitation cascade experiments where animals often move between primary and secondary FS 15 , and taxa were grouped into one-dimensional community abundance and taxonomic richness values so that strong and common species-specific positive relationships overshadow minor weak or infrequent negative relationships 11 . ...
... The experiments were done in natural habitats with low levels of anthropogenic habitat-alterations and with few non-native species (although experiment 16 and 18 had as secondary FS the non-native kelp Undaria pinnatifida, which has colonised open coastlines throughout much of New Zealand). This contrasts other global heterogeneity studies that have focused on modified habitats, like seawalls in harbours, that can be dominated by fouling and invasive species 74 . Controls remained free of secondary FS following initial removal either because secondary FS did not colonise the primary FS (most experiments) or because they were removed throughout the experiments. ...
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Habitat heterogeneity is considered a primary causal driver underpinning patterns of diversity, yet the universal role of heterogeneity in structuring biodiversity is unclear due to a lack of coordinated experiments testing its effects across geographic scales and habitat types. Furthermore, key species interactions that can enhance heterogeneity, such as facilitation cascades of foundation species, have been largely overlooked in general biodiversity models. Here, we performed 22 geographically distributed experiments in different ecosystems and biogeographical regions to assess the extent to which variation in biodiversity is explained by three axes of habitat heterogeneity: the amount of habitat, its morphological complexity, and capacity to provide ecological resources (e.g. food) within and between co-occurring foundation species. We show that positive and additive effects across the three axes of heterogeneity are common, providing a compelling mechanistic insight into the universal importance of habitat heterogeneity in promoting biodiversity via cascades of facilitative interactions. Because many aspects of habitat heterogeneity can be controlled through restoration and management interventions, our findings are directly relevant to biodiversity conservation.
... Worldwide, efforts to enhance biodiversity of artificial structures are on-going (Morris et al. 2019 andO'Shaughnessy et al. 2020b for reviews), including the use of transplantation of ecosystemengineer species to enhance biodiversity of ordinarily depauperate surfaces (Ng et al. 2015, Ferrario et al. 2016. To date, these efforts have received relatively little attention, but trials have indicated promising (Perkol-Finkel et al. 2012), but variable results (Strain et al. 2021). Whilst the use of habitatforming species for restoration efforts has been advocated and may well lead to positive biodiversity outcomes (Byers et al. 2006), care must also be taken advocating the use of invasive and non-native species, without full consideration of the wider environmental implications (Sotka and Byers' (2019) criticism of Ramus et al. (2017)) which may yield unexpected results. ...
Article
Positive species interactions such as facilitation are important for enabling species to persist, especially in stressful conditions, and the nature and strength of facilitation varies along physical and biological gradients. Expansion of coastal infrastructure is creating hotspots of invasive species which can spillover into natural habitats, but the role of positive species interactions associated with biological invasions remains understudied. Theory suggests that stronger biotic pressure in natural habitats inhibits invasion success. In space‐limited marine systems, sessile organisms can overcome this limiting resource by settling as an epibiont on a substrate organism – basibiont. Using a series of spatially extensive surveys, we explored the role of invasive and native basibionts in providing habitat for other invasive and native epibionts, and tested whether environmental context (i.e. if the receiving habitat was natural or artificial), altered ecological outcomes. Overall, provision of space by basibionts was more important for invasive epibionts than for native epibionts but was dependent on the environmental context. Invasive basibionts facilitated invasive epibionts in natural habitats, and appeared to be more important for native epibionts in artificial habitats respectively. Native basibionts facilitated invasive, but not native epibionts in both natural and artificial habitats. These results advance our understanding of facilitation and highlight the idiosyncratic nature of biofouling and epibiosis, and the potentially important influence of environmental context. The degree to which native habitat‐forming species versus invasive habitat‐forming species either do or do not facilitate other native or non‐native species is a rich area for investigation. Experimental work is required to disentangle the processes underpinning these patterns.
... Consequently, the lack of habitat heterogeneity meant that fewer species could be supported on the artificial reef than on the natural reef. However, in an experiment using concrete tiles with three degrees of relief (made of ridges and crevices) it was found that complexity mostly enhances biodiversity and live cover but not always (Strain et al., 2021). Typically, the lower diversity found on artificial reefs in comparison to natural reefs can be explained by the younger age of the artificial reef, because younger reefs have not had the opportunity to establish a mature and comparable community to that of the natural reef (Clark and Edwards, 1999;Perkol-Finkel et al., 2006;Perkol-Finkel and Benayahu, 2009). ...
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A R T I C L E I N F O Keywords: 18th century Artificial reef Crustose coralline algae Turf algae Palythoa caribaeorum Millepora spp. A B S T R A C T With increasing maritime activities in the proximity of coral reefs, a growing number of manmade structures are becoming available for coral colonisation. Yet, little is known about the sessile community composition of such artificial reefs in comparison with that of natural coral reefs. Here, we compared the diversity of corals and their competitors for substrate space between a centuries-old manmade structure and the nearest natural reef at St. Eustatius, eastern Caribbean. The artificial reef had a significantly lower species richness and fewer competitive interactions than the natural reef. The artificial reef was dominated by a cover of crustose coralline algae and zoantharians, instead of turf algae and fire corals on the natural reef. Significant differences in species composition were also found between exposed and sheltered sites on both reefs. Our study indicates that even a centuries-old manmade reef cannot serve as a surrogate for natural reefs.
... Recent efforts have also focused on the restoration of populations of invertebrate species, such as the scleractinian coral Astroides calycularis (Musco et al., 2017), the bryozoan Pentapora fascialis (Pagès-Escolà et al., 2020), and the limpet Patella ferruginea (Ferranti et al., 2021), with many novel technologies and approaches emerging, such as or the use of electro-mineral accretion for enhancing the settlement of the red coral Corallium rubrum (Benedetti et al., 2011). Increasing research has also focused on the bioenhancement of artificial habitats by increasing sur face topographic complexity, or by using more environmentally friendly construction materials, with some successful examples but also uncertainties about the consistency of the benefits (Strain et al., 2021). ...
Article
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Global change is striking harder and faster in the Mediterranean Sea than elsewhere, where high levels of human pressure and proneness to climate change interact in modifying the structure and disrupting regulative mechanisms of marine ecosystems. Rocky reefs are particularly exposed to such environmental changes with ongoing trends of degradation being impressive. Due to the variety of habitat types and associated marine biodiversity, rocky reefs are critical for the functioning of marine ecosystems, and their decline could profoundly affect the provision of essential goods and services which human populations in coastal areas rely upon. Here, we provide an up-to-date overview of the status of rocky reefs, trends in human-driven changes undermining their integrity, and current and upcoming management and conservation strategies, attempting a projection on what could be the future of this essential component of Mediterranean marine ecosystems.
... Recent efforts have also focused on the restoration of populations of invertebrate species, such as the scleractinian coral Astroides calycularis (Musco et al., 2017), the bryozoan Pentapora fascialis (Pagès-Escolà et al., 2020), and the limpet Patella ferruginea (Ferranti et al., 2021), with many novel technologies and approaches emerging, such as or the use of electromineral accretion for enhancing the settlement of the red coral Corallium rubrum (Benedetti et al., 2011). Increasing research has also focused on the bioenhancement of artificial habitats by increasing surface topographic complexity, or by using more environmentally friendly construction materials, with some successful examples but also uncertainties about the consistency of the benefits (Strain et al., 2021). ...
... Depending on logistical factors (eg size of the artificial habitat structure, cost of construction and installation), conducting in-situ experiments at large spatial scales may not be feasible. However, environmental variation across larger spatial scales may greatly influence the effectiveness of an artificial habitat structure (Strain et al. 2021). Consequently, given the inherent risks associated with the use of these structures, we urge researchers and managers to exercise ...
Article
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Habitat destruction and degradation, and their interaction with other threats, are driving animal declines worldwide. One approach increasingly proposed for mitigating these threats is to create artificial habitat structures as substitutes for destroyed natural structures. Here, we provide the first general definition of artificial habitat structures and synthesize important considerations for effective use. We show that they are a versatile conservation tool that have been trialed in a variety of contexts globally, to varying degrees of success. Their design must be well-informed by the drivers of natural habitat selection and their use should be part of an experimental framework to enable evaluation and refinement. We highlight possible ecological risks associated with their use and urge that artificial habitat structures are not used as inappropriate biodiversity offsets or for greenwashing. Looking forward, cross-disciplinary collaborations will help design sophisticated and effective structures to assist animal conservation in this era of rapid global change.
... Epibiosis is a very common phenomenon in marine and estuarine environments, beingobserved in various substrates, culture structures, ship hulls, oil platforms, mangrove roots and different solid environments, which allow the fixation of organisms (Mol et al. 2009;García 2010;Leonard et al. 2017), with the use of artificial collectors being the most appropriate tool to study the colonization patterns of benthic communities (Kaufman et al. 1992;Mendo et al. 2011). Therefore, the identification and quantification of epibionts in a given area, provides important information on the abundance and reproductive behavior of the species and also allows to know the reproductive dynamics of organisms (Leonard et al. 2017;Strain et al. 2020). This information also helps to establish strategies for the conservation, management and repopulation of organisms, for the recovery of their populations; it also helps to identify species of commercial importance and with cultivation projections. ...
Article
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ABSTRACT Artificial collectors are tools that explain the settlement dynamics of marine invertebrates. What is known about these in the Caribbean is very limited. In order to identify and quantify the diversity of epibionts in relation to depth, between December, 2015 and August, 2016, cylindrical collectors were suspended on a long line at varying depths. At each experimental depth, bimonthly temperature, chlorophyll a, and total seston records were obtained. 7,078 individuals belonging to five phyla were counted: Chordata, Echinodermata, Arthropoda, and Mollusca. The mollusks, mainly bivalves, were the most abundant, represented by: Pinctada imbricata, Pteria colymbus, and Crassotrea rhizophorae. The recruitment of organisms showed significant changes over time, with different fixation patterns. Abundance, wealth, and diversity, in each of the experimental depths were modulated by the temperature and phytoplankton biomass and the seston. The collectors, regardless of depth and time, acted as artificial habitats, reflecting the variety of benthic organisms, mainly mollusks, that naturally share the different environments that surround the southern coast of the Gulf of Cariaco, which could be a dynamic observed in the southeast Caribbean. The Gulf of Cariaco is an important ecosystem service due to the larval supply it provides to the environment, related to the fertility of its waters. Keywords: Culture, depth, mollusks, environmental factors
... Reductions in growth rates will not only affect size and fitness, but also reduce molluscs ability to form biogenic structures, limiting their ability to support biodiversity (Strain et al., 2021). Many habitats created by these taxa are protected due to the associated high biodiversity (Donnarumma et al., 2018). ...
Article
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Climate change is impacting organisms in every region of the world ocean by acting though on individuals in response to their local environments. Given projected future risks derived from these changes, it is becoming increasingly important to understand regional signals of how organisms respond to facilitate their governance and protection. Benthic organisms structure ecological compositions and ecosystem dynamics, therefore not only providing insights into their own response to climate change but also how ecosystems might respond to future conditions. European seas are transitional areas including boreal, warm-temperate, and subarctic waters with organisms frequently at limits of their distributions. Here, we use a meta-analytical approach to assess how calcification, growth, metabolism, photosynthesis, reproduction, and survival in European benthic organisms respond to ocean acidification and warming. Using meta-regression, we examine how study design factors influence effect-size outcomes. Longer experimental periods generally amplified the effects of climate change on taxonomic groupings and related physiological traits and against expectation do not result in acclimation. In agreement with global studies, we find that impacts vary considerably on different taxonomic groupings and their physiological traits. We found calcifying organisms are an at-risk taxon in European waters, with climate stressors decreasing growth rates, reproduction, and survival rates. Fleshy algal species demonstrate resilience to climate stressors, suggesting future European benthic ecosystems will undergo restructuring based on current climate emission pathways.
... Depending on logistical factors (eg size of the artificial habitat structure, cost of construction and installation), conducting in-situ experiments at large spatial scales may not be feasible. However, environmental variation across larger spatial scales may greatly influence the effectiveness of an artificial habitat structure (Strain et al. 2021). Consequently, given the inherent risks associated with the use of these structures, we urge researchers and managers to exercise ...
... Ultimately, successful ecological engineering interventions rely on clear project goals (e.g. protecting exploited species, increasing biodiversity or improving water quality), knowledge of local conditions and species requirements (Hsiung et al., 2020;Strain et al., 2021) and social licence . ...
Article
The human population is increasingly reliant on the marine environment for food, trade, tourism, transport, communication and other vital ecosystem services. These services require extensive marine infrastructure, all of which have direct or indirect ecological impacts on marine environments. The rise in global marine infrastructure has led to light, noise and chemical pollution, as well as facilitation of biological invasions. As a result, marine systems and associated species are under increased pressure from habitat loss and degradation, formation of ecological traps and increased mortality, all of which can lead to reduced resilience and consequently increased invasive species establishment. Whereas the cumulative bearings of collective human impacts on marine populations have previously been demonstrated, the multiple impacts associated with marine infrastructure have not been well explored. Here, building on ecological literature, we explore the impacts that are associated with marine infrastructure, conceptualising the notion of correlative, interactive and cumulative effects of anthropogenic activities on the marine environment. By reviewing the range of mitigation approaches that are currently available, we consider the role that eco-engineering, marine spatial planning and agent-based modelling plays in complementing the design and placement of marine structures to incorporate the existing connectivity pathways, ecological principles and complexity of the environment. Because the effect of human-induced, rapid environmental change is predicted to increase in response to the growth of the human population, this study demonstrates that the development and implementation of legislative framework, innovative technologies and nature-informed solutions are vital, preventative measures to mitigate the multiple impacts associated with marine infrastructure.
... These interventions now come under a broad definition of 'nature-based solutions' in a rapidly growing arena of research that aims to address both the climate and biodiversity crisis. Care must be exercised when implementing such solutions, as biodiversity responses differ depending on the environmental context (Strain et al. 2021). But as Firth et al. ...
Chapter
Estuarine and coastal waters are acknowledged centres for anthropogenic impacts. Superimposed on the complex natural interactions between land, rivers and sea are the myriad consequences of human activity – a spectrum ranging from locally polluting effluents to some of the severest consequences of global climate change. For practitioners, academics and students in the field of coastal science and policy, this book examines and exemplifies current and future challenges: from upper estuaries to open coasts and adjacent seas; from tropical to temperate latitudes; from Europe to Australia. This authoritative volume marks the 50th anniversary of the Estuarine and Coastal Sciences Association, and contains a prologue by founding member Professor Richard Barnes and a short history of the Association. Individual chapters then address coastal erosion and deposition; open shores to estuaries and deltas; marine plastics; coastal squeeze and habitat loss; tidal freshwaters – saline incursion and estuarine squeeze; restoration management using remote data collection; carbon storage; species distribution and non-natives; shorebirds; modelling environmental change; physical processes such as sediments and modelling; sea level rise and estuarine tidal dynamics; estuaries as fish nurseries; policy versus reality in coastal conservation; developments in estuarine, coastal and marine management.
Article
Hard coastal protective infrastructure, such as breakwaters, are a common adaptation strategy to protect assets, increase safety and improve navigation by reducing erosion and flood risks along coastlines globally. However, protective structures can have pervasive impacts on use patterns, aesthetics and associated ecosystems, threatening ecosystem goods and services upon which humans depend. Guided by a recent Australian state Government strategy that aims to plan for “a healthy coast and sea managed for the greatest wellbeing of the community, now and into the future”, we present a decision-making support tool for practitioners to help achieve more sustainable solutions to coastal adaptation into the future. Sustainable coastal adaptation needs to consider the environmental and socio-economic consequences of hard protective infrastructure, as well as the increased vulnerability due to rising sea levels. To demonstrate our arguments, we introduce three different coastal scenarios. We also discuss alternatives to coastal protection and make scenario-specific recommendations to enhance environmental and socio-economic outcomes of coastal adaptation. In general, the implementation of hard protective infrastructure should probably be a last resort after retreat and soft approaches have been ruled out as viable options. Where protective infrastructure is the current best option, environmental and socio-economic outcomes can be enhanced using eco-engineering and multi-use features. In the long term, however, retreat from some coastal areas may be necessary and existing infrastructure might be removed or abandoned.
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Aim Understanding the formation and maintenance of biogeographical breaks is fundamental for developing analyses related to biodiversity and conservation. Biogeographical patterns along China's coast are changing dramatically in the face of climate change and alterations in land-use. In this paper, we sought to clarify the mechanisms responsible for the formation and maintenance of a biogeographical barrier on China's coast. Location Coastline of northern China. Methods We have reviewed literature of research related to biogeographical and phylogeographical patterns of intertidal macrobenthos along the coast of Jiangsu Province and adjacent areas, summarized the distribution patterns and biogeographical breakers. We have also reviewed literature about the processes and drivers on coastal biogeographical breaks, to clarify the mechanisms acting to the northward shift of the biogeographical break. Results The Yangtze (Changjiang) River Estuary Biogeographical Barrier (YREBB) at 30°–31°N, which serves as a coastal biogeographical boundary for the Cold Temperate Northwest Pacific Province and the Warm Temperate Northwest Pacific Province for marine species, has moved northward to ~33°–34°N due to the changes in habitat continuity, oceanographic circulation and climate factors. Consequently, a new biogeographic barrier for intertidal macrobenthos, the Subei Biogeographical Barrier (SBB) on the central coast of Jiangsu Province, has emerged. Main conclusions The formation and maintenance of the SBB are closely related to the larval dispersal potential, larval settlement success and post-settlement population establishment, all of which have been profoundly influenced by anthropogenic environmental changes. The northward shift of the YREBB and the appearance of the SBB provide an excellent model system for investigating the impacts of climate change and land-use change on coastal biogeographic patterning and for clarifying the mechanisms underlying the formation and maintenance of biogeographical barriers in the face of the unprecedented environmental changes.
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The current development of human activities at sea (e.g. land reclamation, maritime activity and marine renewable energy) is leading to a significant increase in the number of infrastructures installed in marine settings. These artificial structures provide new hard-bottom habitats for many marine organisms and can thus modify the structure and functioning of coastal ecosystems. In order to better evaluate the nature of these modifications as well as the potential benefits and/or impacts generated, it becomes essential to develop assessment methods that can be applied to a wide variety of study sites from harbours to coastal offshore environments. In this context, our study aims to review the different methods and indicators available which are used to measure the modifications of biodiversity and ecological functioning generated by such structures. Among the methods reviewed, we highlight some that were developed specifically for artificial structures, and others intended for various primary uses but which have been successfully transposed to artificial structures. Nevertheless, we also point out the lack of reliable methods concerning some biological ecosystem components impacted by artificial structures. In this context, we require the adaptation or creation of brand-new indicators to achieve a better characterisation of the ecological impacts generated by these structures. Overall, this study highlights a very high number of existing methods, which provide stakeholders with useful tools to study the impacts of artificial structures, and identifies the need to develop integrative indicators to enhance the deployment of new artificial structures.
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Pre-colonial stonewalled fish traps, an ancient engineering feat in the intertidal region, represent the earliest proof of human manipulation of the coastline in Southern Africa, specifically by the First Indigenous Peoples of South Africa. We investigated the ecologically functioning of a fish trap located on the southeast coast of South Africa from a larval fish and invertebrate perspective. This research was done in collaboration with the Khoi traditional custodians of the area of study. Samples were collected using a light trap on four separate spring tide occasions, deployed for 3 consecutive nights during 2 full moon trips and 2 new moon trips during the known peak larval settlement period (November 2020–February 2021). Although time-dependent, the importance of this novel microhabitat for the development of coastal fishes and invertebrates was highlighted. Even with the high intertidal location of the stonewalled fish trap sampled at Cape Recife, the presence of a pool of permanent non-stagnant water within the fish trap, even during low spring tide, could provide protection to larvae, in the form of more stable environmental conditions, as well as less exposure to marine predators and harsh physical environmental conditions. This research aims to raise awareness of the stonewalled fish traps located on the southeast of South Africa with a view towards developing a more inclusive management of these marine cultural heritage sites, specifically involving the First Indigenous Peoples of South Africa.
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The proliferation of artificial concrete structures (ACSs) in the marine environment causes intertidal habitat loss and is a poor surrogate for natural rocky shores in terms of species richness, abundance, and community composition. As hard engineered coastlines increase, there is growing interest in how new concrete structures can facilitate improved habitat and biodiversity compared to existing concrete structures. Experiments that have substituted cement binder and aggregates in varying proportions and combinations have demonstrated that it is possible to enhance the primary bioreceptivity of concrete, either chemically or via microtopographical texture. This review synthesises key literature and identifies which concrete formulas prove most effective at enhancing bioreceptivity and those that have limited value, providing recommendations for coastal practitioners and for formulas that warrant further study. It is evident that the efficacy of chemical bioreceptivity of concrete is likely to be spatio-temporally limited (months) and enhancing surface roughness should be prioritised as a way to enhance colonisation. However, both chemical and physical methods require further investigation in within in situ marine settings for longer durations (>12 months).
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The marine environment is being increasingly modified by the construction of artificial structures, the impacts of which may be mitigated through eco-engineering. To date, eco-engineering has predominantly aimed to increase biodiversity, but enhancing other ecological functions is arguably of equal importance for artificial structures. Here, we manipulated complexity through habitat structure (flat, and 2.5 cm, 5 cm deep vertical and 5 cm deep horizontal crevices) and seeding with the native oyster (Saccostrea glomerata, unseeded and seeded) on concrete tiles (0.25 m x 0.25 m) affixed to seawalls to investigate whether complexity (both orientation and depth of crevices) influences particle removal rates by suspension feeders and colonisation by different functional groups, and whether there are any ecological trade-offs between these functions. After 12 months, complex seeded tiles generally supported a greater abundance of suspension feeding taxa and had higher particle removal rates than flat tiles or unseeded tiles. The richness and diversity of taxa also increased with complexity. The effect of seeding was, however, generally weaker on tiles with complex habitat structure. However, the orientation of habitat complexity and the depth of the crevices did not influence particle removal rates or colonising taxa. Colonisation by non-native taxa was low compared to total taxa richness. We did not detect negative ecological trade-offs between increased particle removal rates and diversity and abundance of key functional groups. Our results suggest that the addition of complexity to marine artificial structures could potentially be used to enhance both biodiversity and particle removal rates. Consequently, complexity should be incorporated into future eco-engineering projects to provide a range of ecological functions in urbanised estuaries.
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Urbanization is leading to biodiversity loss through habitat homogenization. The smooth, featureless surfaces of many marine urban structures support ecological communities, often of lower biodiversity, distinct from the complex natural habitats they replace. Eco-engineering (design for ecological co-benefits) seeks to enhance biodiversity and ecological functions on urban structures. We assessed the benefits to biodiversity of retrofitting four types of complex habitat panels to an intertidal seawall at patch (versus flat control panels) and site (versus unmodified control seawalls and reference rocky shores) scales. Two years after installation, patch-scale effects of complex panels on biodiversity ranged from neutral to positive, depending on the protective features they provided, though all but one design (honeycomb) supported unique species. Water-retaining features (rockpools) and crevices, which provided moisture retention and cooling, increased biodiversity and supported algae and invertebrates otherwise absent. At the site scale, biodiversity benefits ranged from neutral at the high- and mid-intertidal to positive at the low-intertidal elevation. The results highlight the importance of matching eco-engineering interventions to the niche of target species, and environmental conditions. While species richness was greatest on rockpool and crevice panels, the unique species supported by other panel designs highlights that to maximize biodiversity, habitat heterogeneity is essential. This article is part of the theme issue ‘Ecological complexity and the biosphere: the next 30 years’.
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The construction of artificial structures, such as seawalls, is increasing globally, resulting in loss of habitat complexity and native species biodiversity. There is increasing interest in mitigating this biodiversity loss by adding topographic habitat to these structures, and/or seeding them with habitat-forming species. Settlement tile experiments, comparing colonisation of species to more and less complex habitats, have been used to inform eco-engineering interventions prior to their large-scale implementation. Most studies have focused on applying one type of intervention (either adding habitat structure or seeding with native organisms), so it is unclear whether there are greater benefits to biodiversity when multiple interventions are combined. Using a fully orthogonal experiment, we assessed the independent and interactive effects of habitat structure (flat vs. crevice/ridges) and seeding with native oysters (unseeded vs. seeded) on the biodiversity of four different functional groups (sessile and mobile taxa, cryptobenthic and pelagic fishes). Concrete tiles (flat unseeded, flat seeded, complex unseeded and complex seeded) were deployed at two sites in Sydney Harbour and monitored over 12 months, for the survival and colonisation of oysters and the species density and abundances of the four functional groups. The survival of seeded oysters was greater on the complex than flat tiles, at one of the two sites, due to the protective role of crevices. Despite this, after 12 months, the species density of sessile invertebrates and the percentage cover of seeded and colonising oysters did not differ between complex and seeded tiles each of which supported more of these variables than the flat unseeded tiles. In contrast, the species density of mobile invertebrates and cryptobenthic fishes and the MaxN of pelagic fishes, at 1 month, were only positively influenced by seeding with oysters, which provided food as well as habitat. Within the complex seeded and unseeded tiles, there was a greater species density of sessile taxa, survival and percentage cover of oysters in the crevices, which were more humid and darker at month 12, had lower high temperature extremes at months 1 and 12, than on the ridges or flat tiles. Our results suggest that eco-engineering projects which seek to maximise the biodiversity of multiple functional groups on seawalls, should apply a variety of different microhabitats and habitat-forming species, to alter the environmental conditions available to organisms.
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1. Climate change and coastal urbanisation are driving the replacement of natural habitats with artificial structures and reclaimed land globally. These novel habitats are often poor surrogates for natural habitats. 2. The application of integrated greening of grey infrastructure (IGGI) to artificial shorelines demonstrates how multifunctional structures can provide biodiversity benefits whilst simultaneously serving their primary engineering function. IGGI is being embraced globally, despite many knowledge gaps and limitations. It is a management tool to compensate anthropogenic impacts as part of the Mitigation Hierarchy. There is considerable scope for misuse and ‘greenwashing’ however, by making new developments appear more acceptable, thus facilitating the regulatory process. 3. We encourage researchers to exercise caution when reporting on small‐scale experimental trials. We advocate that greater attention is paid to when experiments ‘fail’ or yield unintended outcomes. We advise revisiting, repeating and expanding on experiments to test responses over broader spatio‐temporal scales to improve the evidence base. 4. Synthesis and applications . Where societal and economic demand makes development inevitable, particular attention should be paid to avoiding, minimising and rehabilitating environmental impacts. Integrated greening of grey infrastructure (IGGI) should be implemented as partial compensation for environmental damage. Mutual benefits for both humans and nature can be achieved when IGGI is implemented retrospectively in previously‐developed or degraded environments. We caution however, that any promise of net biodiversity gain from new developments should be scrutinised and any local ecological benefits set in the context of the wider environmental impacts. A ‘greened’ development will always impinge on natural systems, a reality that is much less recognised in the sea than on land.
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Coastal urbanisation, energy extraction, food production, shipping and transportation have led to the global proliferation of artificial structures within the coastal and marine environments (sensu "ocean sprawl"), with subsequent loss of natural habitats and biodiversity. To mitigate and compensate impacts of ocean sprawl, the practice of eco-engineering of artificial structures has been developed over the past decade. Eco-engineering aims to create sustainable ecosystems that integrate human society with the natural environment for the benefit of both. The science of eco-engineering has grown markedly, yet synthesis of research into a user-friendly and practitioner-focused format is lacking. Feedback from stakeholders has repeatedly stated that a "photo user guide" or "manual" covering the range of eco-engineering options available for artificial structures would be beneficial. However, a detailed and structured "user guide" for eco-engineering in coastal and marine environments is not yet possible; therefore we present an accessible review and catalogue of trialled eco-engineering options and a summary of guidance for a range of different structures tailored for stakeholders and end-users as the first step towards a structured manual. This work can thus serve as a potential template for future eco-engineering guides. Here we provide suggestions for potential eco-engineering designs to enhance biodiversity and ecosystem functioning and services of coastal artificial structures with the following structures covered: (1) rock revetment, breakwaters and groynes composed of armour stones or concrete units; (2) vertical and sloping seawalls; (3) over-water structures (i.e., piers) and associated support structures ; and (4) tidal river walls.
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Non-indigenous species (NIS) are one of the leading forces of change in coastal marine ecosystems and are often associated with fouling communities, especially the artificial structures of marinas and ports. As a result, monitoring of marine fouling communities is crucial to evaluate the introduction and spread of NIS as well as assess the efficacy of legislation aimed to prevent further introductions. Settlement plates have long been used as a means of studying fouling communities. Many factors such as orientation, movement, and substrate type have been shown to influence the number and type of organisms present in fouling communities, but one key question remains poorly studied: how well do settlement plates represent the established fouling community of a marina, especially regarding NIS? We investigated this question, by examining the sessile invertebrates on both marina structures and settlement plates from three marinas in San Francisco Bay (California, USA). Total species richness, NIS richness, and community composition on settlement plates were found to be similar to those on existing marina floating docks. Our results indicate that settlement plates can provide a sensitive and standardized measure of the NIS richness and composition in fouling communities.
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Increasingly, urbanised coastlines are being armoured by shoreline protection structures, such as seawalls. Seawalls typically lack the complex microhabitats and protective spaces of natural shorelines and consequently organisms that settle on them may be particularly susceptible to predation. We tested whether the addition of complex microhabitats to seawalls enhances the survivorship of oysters, key habitat-forming species on intertidal shores, by reducing the intensity of predation. At two sites in Sydney Harbour, we compared the magnitude and sources of mortality of juvenile oysters among (1) flat tiles, without crevices or ridges; (2) complex tiles, with 2.5 cm high ridges, separated by crevices; and (3) complex tiles, with 5 cm high ridges, separated by crevices. We also compared predatory fish visitation and feeding among sites and treatments using GoPro® cameras. The abundance and feeding of predatory fish was much greater at one of the study sites than the other, but at neither site differed among treatments. At the site with greater predatory fish abundances, survivorship of juvenile oysters was 50% greater on the 5 cm complex tiles than flat tiles, and on complex tiles approximately 300% greater in crevices than on ridges. Of the dead oysters, almost all were cracked, indicative of fish predation. In contrast, at the site with fewer predatory fish, there were no detectable differences in oyster survivorship between treatments. These results suggest that the addition of complex habitat to seawalls could be an effective strategy in reducing fish predation pressure on juvenile oysters at sites with abundant predatory fish. A greater understanding of the site-specific pressures is required to enhance the abundances of desirable species and functions on seawalls.
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With the ongoing loss of coral cover and the associated flattening of reef architecture, understanding the links between coral habitat and reef fishes is of critical importance. Here, we investigate whether considering coral traits and functional diversity provides new insights into the relationship between structural complexity and reef fish communities, and whether coral traits and community composition can predict structural complexity. Across 157 sites in Seychelles, Maldives, the Chagos Archipelago, and Australia’s Great Barrier Reef, we find that structural complexity and reef zone are the strongest and most consistent predictors of reef fish abundance, biomass, species richness, and trophic structure. However, coral traits, diversity, and life histories provided additional predictive power for models of reef fish assemblages, and were key drivers of structural complexity. Our findings highlight that reef complexity relies on living corals—with different traits and life histories—continuing to build carbonate skeletons, and that these nuanced relationships between coral assemblages and habitat complexity can affect the structure of reef fish assemblages. Seascape-level estimates of structural complexity are rapid and cost effective with important implications for the structure and function of fish assemblages, and should be incorporated into monitoring programs.
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A checklist of 118 Singaporean species of Bryozoa (3 Cyclostomata, 7 Ctenostomata, 108 Cheilostomata) and three taxa of Entoprocta is presented, based upon sampling during recent workshops (2012–2014), registered museum material, incidental collecting and historical records. Accordingly, many species are reported for the first time from Singaporean waters, including a freshwater bryozoan (Hislopia malayensis), numerous marine bryozoans and an entoproct (Pedicellina sp.). Several easily collected intertidal species, including a population of the globally rare mangrove epiphyte Amphibiobeania epiphylla and certain alien-invasive taxa, are amenable to research on their biology (growth and reproduction) and ecology.
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Habitat structure influences the diversity and distribution of organisms, potentially affecting their response to disturbances by either affecting their ‘susceptibility’ or through the provision of resources that can mitigate impacts of disturbances. Chemical disturbances due to contamination are associated with decreases in diversity and functioning of systems and are also likely to increase due to coastal urbanisation. Understanding how habitat structure interacts with contaminants is essential to predict and therefore manage such effects, minimising their consequences to marine systems. Here, we manipulated two structurally different habitats and exposed them to different types of contaminants. The effects of contamination and habitat structure interacted, affecting species richness. More complex experimental habitats were colonized by a greater diversity of organisms than the less complex habitats. These differences disappeared, however, when habitats were exposed to contaminants, suggesting that contaminants can override effects of habitats structure at small spatial scales. These results provide insight into the complex ways that habitat structure and contamination interact and the need to incorporate evidence of biotic responses from individual disturbances to multiple stressors. Such effects need to be taken into account when designing and planning management and conservation strategies to natural systems.
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Imagery collected by still and video cameras is an increasingly important tool for minimal impact, repeatable observations in the marine environment. Data generated from imagery includes identification, annotation and quantification of biological subjects and environmental features within an image. To be long-lived and useful beyond their project-specific initial purpose, and to maximize their utility across studies and disciplines, marine imagery data should use a standardised vocabulary of defined terms. This would enable the compilation of regional, national and/or global data sets from multiple sources, contributing to broad-scale management studies and development of automated annotation algorithms. The classification scheme developed under the Collaborative and Automated Tools for Analysis of Marine Imagery (CATAMI) project provides such a vocabulary. The CATAMI classification scheme introduces Australian-wide acknowledged, standardised terminology for annotating benthic substrates and biota in marine imagery. It combines coarse-level taxonomy and morphology, and is a flexible, hierarchical classification that bridges the gap between habitat/biotope characterisation and taxonomy, acknowledging limitations when describing biological taxa through imagery. It is fully described, documented, and maintained through curated online databases, and can be applied across benthic image collection methods, annotation platforms and scoring methods. Following release in 2013, the CATAMI classification scheme was taken up by a wide variety of users, including government, academia and industry. This rapid acceptance highlights the scheme's utility and the potential to facilitate broad-scale multidisciplinary studies of marine ecosystems when applied globally. Here we present the CATAMI classification scheme, describe its conception and features, and discuss its utility and the opportunities as well as challenges arising from its use.
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Scientists recognize the importance of ecological data prior to invasion by non-native species in order to evaluate changes in the recipient community. Here we assess the potential impact of the invasion of the bivalve Isognomon bicolor (C.B. Adams, 1845) on Brazilian rocky shores through the use of surveys both before and after the arrival of this non-native species. The invader was mostly distributed across the mid and low shore levels of the intertidal zone with relative abundance ranging from 9.0 to 36.7 percent cover. The mid shore, previously dominated by the native barnacle Tetraclita stalactifera (Lamarck, 1818), was co-dominated by this barnacle species and I. bicolor after invasion. The relative abundance of these species, and presumably the interaction strength between them, differed between sites. At the site where I. bicolor reached the highest abundance (around 30% on average), the abundance of T. stalactifera decreased on average 70% compared to baseline values obtained before the I. bicolor invasion. Finally, conspicuous and extensive I. bicolor beds such as those observed in this study have not been reported in its original distribution range. Beds of I. bicolor may create a much more intricate biogenic matrix than the extents of bare rock and barnacle clumps it replaced. This bivalve may act as an ecosystem engineer and, thus a functionally different component of the intertidal community in its invaded range compared to its native distribution.
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We studied the influence of piscivorous fishes and prey refuges on assemblages of fishes occupying 52 model reefs in a large seagrass bed off St. Thomas, U.S. Virgin Islands. We conducted three experiments: two involving 6 reefs each, lasting 2 and 5 yr, and one involving 40 reefs, lasting 1 yr. Each experiment included replicate reefs in various combinations of five structural treatments: holeless controls, 12 and 24 small holes, and 12 and 24 large holes. Tagging studies indicated that the reefs were sufficiently isolated from each other to comprise statistically independent replicates, and that resident piscivores occupied home reefs. We observed 97 species on or near the reefs, representing all major foraging guilds, and each holed reef supported hundreds of individuals. We examined four categories of fish: (1) large reef associates (too large for the small holes; most of these fish were both predators on smaller fish and prey for larger transient piscivores), (2) moray eels (piscivores that could fit into the small holes), (3) small reef associates (potential prey that could fit into the small holes), and (4) juvenile grunts (potential prey that sporadically were extremely abundant). We tested five a priori predictions of the general hypothesis that predation is an important process structuring reef-fish assemblages. The first two predictions dealt with the role of prey refuges. First, if reef holes function as prey refuges, then prey fish should be most abundant on reefs providing holes near their body diameters, because such holes would make the prey fish safest from predation. Seven of eight experimental comparisons supported this prediction, and five of them were statistically significant. Second, if refuge availability limits prey abundance, then prey fish should be more abundant on reefs with 12 holes than those with no holes, and should be more abundant on reefs with 24 holes than those with 12 holes. The first part of this prediction was verified by all nine experimental comparisons, seven of which were statistically significant. However, there were no strong differences between 12-hole and 24-hole reefs. Thus, between 0 and 12 holes per reef, holes limited local prey populations; between 12 and 24 holes per reef, the number of holes was not limiting. Several lines of evidence suggested that the latter pattern was due to temporary saturation of the study area with refuges when we added 40 reefs to 12 existing reefs. The remaining three predictions dealt directly with the community-level role of predation. First, predators should affect local prey abundance either chronically, in which case a negative relationship among reefs is predicted between the average abundances of predators and prey, or sporadically, in which case a negative relationship is predicted between the abundance of predators and the maximum number of co-occurring prey ever observed at each predator abundance. The former prediction was falsified, whereas the latter was verified. Observations of extreme type III survivorship of recruit cohorts on reefs with many piscivores and occasional direct observations of piscivory bolstered the conclusion that this relationship was causal. Finally, we predicted that predators should affect the number of prey species on a reef. We observed a significant negative relationship among reefs between predator abundance and maximum prey-species richness. Comparing species' relative abundances on reefs at the extremes of this regression, piscivores appear to have nonselectively reduced and extirpated both common and rare prey species, although this relationship remains purely correlative. In our model system, high local species diversity appears to have been maintained despite rather than because of predation. We propose a conceptual model where the local abundances of coral-reef fishes are determined by the relative magnitudes of recruitment by larvae, colonization by juveniles and adults, predation, and competition for refuges, each of which varies through time and space. Multifactorial field experiments will be necessary to test such pluralistic hypotheses.
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Habitat complexity is one of the most important factors structuring biotic assemblages, yet we still lack basic understanding of the underlying mechanisms. Although it is one of the primary targets in conservation management, no methods are available for comparing complexity across ecosystems, and system-specific qualitative assessment predominates. Despite its overwhelming importance for faunal diversity and abundance, there has been surprisingly little interest in examining its effects on other community and ecosystem attributes. We discuss possibilities of such effects, outlining potentially fruitful areas for future research, and argue that complexity may be implicated in community persistence and ecosystem stability by acting as a decoupling mechanism in predator–prey interactions. We provide a brief overview of methods used to quantify complexity in different ecosystems, highlighting contributions of the current issue of Hydrobiologia, and discuss potential application of these approaches for cross-ecosystem comparisons. Better understanding of the role of habitat complexity resulting from such comparisons is critically important for preservation of biodiversity and ecosystem function in an era of unprecedented habitat loss.
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Environmental heterogeneity is regarded as one of the most important factors governing species richness gradients. An increase in available niche space, provision of refuges and opportunities for isolation and divergent adaptation are thought to enhance species coexistence, persistence and diversification. However, the extent and generality of positive heterogeneity–richness relationships are still debated. Apart from widespread evidence supporting positive relationships, negative and hump-shaped relationships have also been reported. In a meta-analysis of 1148 data points from 192 studies worldwide, we examine the strength and direction of the relationship between spatial environmental heterogeneity and species richness of terrestrial plants and animals. We find that separate effects of heterogeneity in land cover, vegetation, climate, soil and topography are significantly positive, with vegetation and topographic heterogeneity showing particularly strong associations with species richness. The use of equal-area study units, spatial grain and spatial extent emerge as key factors influencing the strength of heterogeneity–richness relationships, highlighting the pervasive influence of spatial scale in heterogeneity–richness studies. We provide the first quantitative support for the generality of positive heterogeneity–richness relationships across heterogeneity components, habitat types, taxa and spatial scales from landscape to global extents, and identify specific needs for future comparative heterogeneity–richness research.
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Biological introductions can alter the ecology of local assemblages and are an important driver of global environmental change. The first step towards understanding the impact of a non-indigenous species is to study its distribution and associations in the invaded area. In Sydney Harbour, the non-indigenous isopod Cirolana harfordi has been reported in densities up to 0.5 individuals per cm(2) in mussel-beds. Abundances of this species have, however, been largely overlooked in other key habitats. The first aim of this study was to evaluate the abundances and distribution of C. harfordi across different habitats representative of Sydney Harbour. Results showed that C. harfordi occurred in oyster and mussel-beds, being particularly abundant in oyster-beds. We also aimed to determine the role of C. harfordi as a predator, scavenger and detritus feeder by investigating the relationships between densities of C. harfordi and (i) the structure of the resident assemblages, and (ii) deposited organic matter in oyster-beds. Densities of C. harfordi were not related to the structure of the assemblages, nor amounts of deposited organic matter. These findings suggested little or no ecological impacts of C. harfordi in oyster-beds. These relationships may, however, affect other variables such as growth of individuals, or be disguised by high variability of assemblages among different locations. Future studies should, therefore, test the impacts of C. harfordi on the size of organisms in the assemblage and use manipulative experiments to control for spatial variation. This study is the first published work on the ecology of the invasion of C. harfordi and provides the starting-point for the study of the impacts of this species in Sydney Harbour.
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The structure of a tropical rocky intertidal community on Taboguilla Island on the Pacific coast of Panama is characterized by extremely low abundances of noncrustose algae and sessile animals, indistinct vertical zonation patterns (a result of the low abundances), and the occur- rence of most invertebrates (except barnacles) and upright algae in holes and crevices (as opposed to open, smooth surfaces). This contrasts strikingly with two temperate rocky intertidal communities, which have high covers of plants and animals, more obvious zones, and invertebrates and upright algae occurring both on relatively homogeneous surfaces and in holes and crevices. Field experiments were done and observations were made in the Panama community to test the effects of different types of consumers (both predators and herbivores) on their prey and on the types of escapes utilized by the prey. Consumer exclusion experiments suggest that (1) predation and herbivory are severe at all times of the year, (2) consumer pressure is a cumulative function of many types and species of predators and herbivores, (3) the primary effect of larger fishes and crabs is to restrict most prey to three-dimensional refuges (holes and crevices), and (4) the primary effect of smaller consumers, mostly invertebrates, is to keep abundances of the prey low. Thus, in the Panama system, three-dimensional space (holes and crevices) appears to be partic- ularly important as a refuge from consumers, while escapes from consumers in body size, time, or two-dimensional space (e.g., in a higher zone) documented so frequently in temperate areas, assume secondary importance for many prey. This restriction of the types of escapes utilized by prey species appears to be a consequence of two main factors: the presence of fast-moving consumers (i.e., herbivorous and predaceous fishes and herbivorous crabs which are absent or rare in the two tem- perate communities), and the year-round foraging of all consumers.
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Anthropogenic modifications to waterways are common and their ecological consequences must be understood to effectively conserve local biodiversity. The facilitation of recreational boating activities often requires substantial alteration of natural areas, however the environmental and ecological consequences of such alterations are rarely described in the scientific literature. In this study, ecological and physico-chemical conditions were investigated in a recreational boating marina, located inside a marine park on the south-east coast of Australia. Recruitment panels were deployed for 8 weeks both inside and outside the marina, and differences in the composition of the developing fouling communities were observed. The recruitment of taxa, which often have short-lived larvae, was increased inside the marina (bryozoans, spirorbids and sponges) while the recruitment of taxa, which often have longer-lived larvae, was reduced or absent (barnacles, solitary ascidians and non-spirorbid polychaetes). Differences were also observed in environmental conditions inside the marina cf. directly outside. The marina environment had higher turbidity, temperature and pH along with higher concentrations of lead and copper in suspended sediments, while flow rates and trapped sediment loads were reduced inside the marina. The differences observed in the study suggest that there may be marked environmental changes associated with marina developments. The potential ecological consequences of these changes should be a primary consideration during the planning process, particularly for developments in locations of notable ecological value.
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Intertidal seawalls are increasingly being built in urban estuaries, fragmenting and replacing natural intertidal shores. Many species of animals and plants live on seawalls. Previous work in Sydney Harbour has shown that common species live on seawalls and rocky shores, but vary in their relative abundances according to height on the shore and location. The potential value of seawalls to provide viable intertidal habitat will depend on their ability to support the full diversity of intertidal species, including those that are relatively rare. This study examines the diversity of animals and plants at 2 heights on rocky shore and seawalls, at 4 locations in Sydney Harbour, using presence/absence measures in an intensive sampling schedule in each habitat. The total number and types of taxa found were very variable within and among locations, but clear patterns arose when the data were combined (800 quadrats in each habitat). With few exceptions, algae and sessile animals were similarly distributed across habitats, but approximately 50% of the mobile animals were not found on seawalls. In addition, rocky shores had a greater proportion of rare taxa (only found in 1 or very few quadrats). Of the shared taxa, patterns of occurrence were similar on the 2 structures. Potential reasons for these patterns are discussed and ways to improve seawalls as a habitat for mobile animals are proposed.
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Coastal ecosystems are under growing pressure from human activities such as pollution and climate change. Although the rapidly growing numbers of humans living in coastal areas is a large part of the problem, there is great opportunity to improve the resistance and resilience of biotic communities via creative changes to the engineering design of built infrastructure. Here, we apply ecological theories to create a framework for adaptive building in marine systems that can be applied by managers worldwide. We explain how climate effects could be mitigated across different spatial scales with both physical and biological interventions. This requires an approach based on ecological theory that incorporates our understanding of how systems withstand (resistance) or recover (resilience) from impacts and takes into account future local and global environmental conditions. By translating ecological theory into practical application, we propose a framework for the choice and design of coastal infrastructure that can underpin effective, forward-looking conservation strategies.
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In this review we provide an overview of the Derwent estuary, Tasmania, Australia. The Derwent flows through the centre of Hobart, a city with a population of approximately 200,000 people. It provides a mechanism for trade and transport, and plays a key role in community recreation. There is significant metal contamination throughout the estuary as a result of historic industry practices, to the extent that the Derwent has an unenvied reputation as one of the most highly metal polluted estuaries in the world. The most recent sediment survey (2012) showed zinc, copper, lead, cadmium, arsenic and mercury levels as still particularly high; with levels in the mid-estuary exceeding 14000, 550, 1800, 120, 420 and 45 ug/g respectively. Zinc is the most abundant metal contaminant in the Derwent, with water column levels in the mid-estuary ranging between 30–60 ug/L. Considerable management and research efforts over the last 50 years have been focused on addressing these legacy issues. As a result, the Derwent Estuary Program was instigated and has proven to be a highly successful body for co-ordination of both remediation and research efforts in the estuary. Whilst the legacy issues have been a key focus for management to date, like other waterbodies worldwide, the estuary is also facing contemporary issues associated with increased urbanisation, changes in catchment usage and climate change. This review provides a comprehensive summary of management initiatives and research to date, and outlines those emerging issues.
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As most port areas throughout the world, Guanabara Bay (GB), which hosts the Harbour of Rio de Janeiro (HRJ), is under intense environmental stress. Located in one of the most iconic places of the world, GB environmental status has been the focus of worldwide attention with the imminent 2016 Olympic Games. The aim of this study was to discuss all past and current relevant aspects to characterize the environment of GB and its main harbour, including geomorphology, climatology, hydrology, geography and biodiversity aspects. A historical view of the social and economic setting, as well as the major threats to the bay environment such as increased pollution, sedimentation, marine debris, cultural eutrophication, bioinvasions, resource utilization, climate change and habitat loss discussed. Aiming to identify – and possibly manage – the threats to biodiversity in harbour areas, a case study comparing the HRJ with the nearby Arraial do Cabo harbour was included. At last, conclusions were drawn so as to highlight effective measures to reduce the environmental degradation of the bay and the harbour.
Article
Habitat complexity is accepted as a general mechanism for increasing the abundance and diversity of communities. However, the circumstances under which complexity has the strongest effects are not clear. Over 20 degrees of Australia's east coast, we tested whether the effects of within‐site structural habitat complexity on the diversity and community structure of sessile marine invertebrates was consistent over a latitudinal gradient where environmental conditions and species composition vary. We used experimental arrays with varied structural treatments to detect whether community cover, species richness, diversity and community composition (β‐diversity) changed with increasing complexity. Community response to complexity varied over latitude due to differences in species richness and community development. Increased complexity had the greatest positive effects on community cover and species richness at higher latitudes where recruitment and growth were low. At lower latitudes, community cover and species richness were higher overall and did not vary substantially between complexity treatments. Latitudinal variation in within‐treatment β‐diversity relative to complexity further suggest divergent community responses. At higher latitudes, increased similarity in more complex treatments suggests community dominance of successful taxonomic groups. Despite limited effects on species richness and community cover at lower latitudes, β‐diversity was higher in more complex treatments, signifying potential positive effects of increased complexity at these sites. These results demonstrate the context‐dependency of complexity effects in response to variation in species richness and community development and should be taken into consideration to help direct conservation and restoration efforts. This article is protected by copyright. All rights reserved.
Article
Ecological theory predicts that positive interactions among organisms will increase across gradients of increasing abiotic stress or consumer pressure. This theory has been supported by empirical studies examining the magnitude of ecosystem engineering across environmental gradients and between habitat settings at local scale. However, predictions that habitat setting, by modifying both biotic and abiotic factors, will determine large-scale gradients in ecosystem engineering have not been tested. A combination of manipulative experiments and field surveys assessed whether along the east Australian coastline: (1) facilitation of invertebrates by the oyster Saccostrea glomerata increased across a latitudinal gradient in temperature; and (2) the magnitude of this effect varied between intertidal rocky shores and mangrove forests. It was expected that on rocky shores, where oysters are the primary ecosystem engineer, they would play a greater role in ameliorating latitudinal gradients in temperature than in mangroves where they are a secondary ecosystem engineer living under the mangrove canopy. On rocky shores, the enhancement of invertebrate abundance in oysters as compared to bare microhabitat decreased with latitude, as the maximum temperatures experienced by intertidal organisms diminished. By contrast, in mangrove forests, where the mangrove canopy resulted in maximum temperatures that were cooler and of greater humidity than on rocky shores, we found no evidence of latitudinal gradients of oyster effects on invertebrate abundance. Contrary to predictions, the magnitude by which oysters enhanced biodiversity was in many instances similar between mangroves and rocky shores. Whether habitat-context modifies patterns of spatial variation in the effects of ecosystem engineers on community structure will depend, in part, on the extent to which the environmental amelioration provided by an ecosystem engineer replicates that of other co-occurring ecosystem engineers. This article is protected by copyright. All rights reserved.
Article
In many parts of the world, shorelines of estuaries are being modified because of increasing urban infrastructure. Consequently, habitats are being lost and replaced by other, artificial habitats, or are being severely modified in deleterious ways. Management of these changes requires recognition of the types of changes that are being made to estuarine shorelines, what sorts of impacts they cause and what sorts of managerial intervention are possible or desirable. Because experimentation in these managed habitats is in its early stages, it is important to provide sound ecological advice based on realistic hypotheses about consequent ecological changes. Wherever possible, management should be evaluated by well-planned experiments, involving analyses of changes in managed areas compared with changes in appropriate control areas. Where the goals of managerial action are the recovery of assemblages of species, what happens in managed areas should also be compared by equivalence tests with what happens in reference areas or relative to pre-defined ecological measures of what would constitute recovery. Here, different types of altered habitats, impacts, ecological changes and purposes of management are discussed. The needs for and nature of different types of hypotheses, experiments and analyses are reviewed with reference to relevant examples.
Book
This new edition to the classic book by ggplot2 creator Hadley Wickham highlights compatibility with knitr and RStudio. ggplot2 is a data visualization package for R that helps users create data graphics, including those that are multi-layered, with ease. With ggplot2, it's easy to: • produce handsome, publication-quality plots with automatic legends created from the plot specification • superimpose multiple layers (points, lines, maps, tiles, box plots) from different data sources with automatically adjusted common scales • add customizable smoothers that use powerful modeling capabilities of R, such as loess, linear models, generalized additive models, and robust regression • save any ggplot2 plot (or part thereof) for later modification or reuse • create custom themes that capture in-house or journal style requirements and that can easily be applied to multiple plots • approach a graph from a visual perspective, thinking about how each component of the data is represented on the final plot This book will be useful to everyone who has struggled with displaying data in an informative and attractive way. Some basic knowledge of R is necessary (e.g., importing data into R). ggplot2 is a mini-language specifically tailored for producing graphics, and you'll learn everything you need in the book. After reading this book you'll be able to produce graphics customized precisely for your problems, and you'll find it easy to get graphics out of your head and on to the screen or page. New to this edition:< • Brings the book up-to-date with ggplot2 1.0, including major updates to the theme system • New scales, stats and geoms added throughout • Additional practice exercises • A revised introduction that focuses on ggplot() instead of qplot() • Updated chapters on data and modeling using tidyr, dplyr and broom
Article
The effective use of ecosystem engineers in biodiversity conservation is contingent on an understanding of those factors that influence the magnitude and direction of their effects. At patch scales, effects of ecosystem engineers on associated communities can range from positive to negative according to how the ecosystem engineer modifies environmental conditions. In a metaanalysis of 68 empirical studies, we assessed how, for a widespread group of ecosystem engineers- the marine habitat-forming bivalves-bivalve taxon, density, habitat, tidal elevation and latitude, as well as habit, or lifestyle, of associated taxa, influences the magnitude and direction of their effect on associated invertebrates. Overall, marine bivalves had a positive effect on both species abundance and species density, but effect sizes varied considerably according to bivalve traits and environmental setting. Oysters enhanced invertebrate abundance to a greater extent than either mussels or pinnids, perhaps because of the greater habitat heterogeneity they provide. Nevertheless, the effect of mussels on associated communities was generally more responsive to spatial variation in engineer traits and environmental context than the effect of oysters or pinnids. Positive effects of mussels on associated species abundance decreased at high mussel densities, were greater at subtidal than mid-low intertidal elevations and differed among faunal habits depending on habitat setting. Knowledge of those conditions under which positive effects of bivalves on associated biodiversity is greatest will help in identifying which species of ecosystem engineer, at which sites, should be prioritised for conservation and restoration, where the goal is enhancement of biodiversity.
Article
Sydney’s Harbour is an integral part of the city providing natural, social, and economic benefits to 4.84 million residents. It has significant environmental value including a diverse range of habitats and animals. A range of anthropogenic and environmental pressures threatens these including loss and modification of habitats, oversupply of nutrients and introduction of pollutants such as metals, organics, and microplastics, introduction of non-indigenous species and the impacts of recreational fishing. Many people now recognise not only the environmental value of Sydney Harbour, but also the economic and social benefits a healthy harbour provides. Over 80% of residents recognise the importance of maintaining a pollution-free coastal environment and conserving the Harbour’s abundant and diverse marine life. A recent review gathered information to make some first estimates of economic revenues and values associated with Sydney Harbour. Port and maritime revenues ($430 million/yr), ferries ($175 million/yr), cruise ship expenditure ($1025 million/yr), major foreshore events such as New Year’s Eve and the Sydney Festival ($400 million/yr), and also income from culture, heritage, arts and science (over $33 million/yr) inject considerable funds into the Australian economy. Notably, proximity to the harbour enhances Sydney domestic real estate capital by an estimated $40 billion, equivalent to $3775 million/yr and biological ecosystem services were valued at $175 million/yr. Here we provide i) a synthesis of our current understanding of the natural, social, and economic resources of Sydney Harbour, ii) the threats and pressures these resources face, and finally iii) how a new marine management framework is being used to address these threats to the natural, social and economic wellbeing of Sydney Harbour. This review clearly shows that Sydney Harbour is a valuable and valued environment that deserves continuing scientific, social, and economic research to support management now and in the future.
Article
Plymouth Sound and adjacent estuaries, UK has been used as a working harbour throughout the ages and has a place in maritime history as the port from where the Pilgrim Fathers left for North America in 1620 on the Mayflower and Charles Darwin departed from on the HMS Beagle on his trip to Galapagos in 1831. Today, it remains a working harbour, home to the largest naval base in Western Europe, the host of numerous cruise ships and recreational boats, yet its complex of estuaries (Tamar, Plym, Lynher) and creeks is nationally and internationally recognised as of conservation importance due to its physical characteristics and flora and fauna. Here, we briefly recount the history and importance of Plymouth through the ages in terms of its historic use as a harbour, its marine science heritage and importance on the international stage. We also briefly describe its ecology.
Article
Ecological theory predicts that positive interactions among organisms will increase across gradients of increasing abiotic stress or consumer pressure. This theory has been supported by empirical studies examining the magnitude of ecosystem engineering across environmental gradients and between habitat settings at local scale. Predictions that habitat setting, by modifying both biotic and abiotic factors, will determine large-scale gradients in ecosystem engineering have not been tested, however. A combination of manipulative experiments and field surveys assessed whether along the east Australian coastline: (1) facilitation of invertebrates by the oyster Saccostrea glomerata increased across a latitudinal gradient in temperature; and (2) the magnitude of this effect varied between intertidal rocky shores and mangrove forests. It was expected that on rocky shores, where oysters are the primary ecosystem engineer, they would play a greater role in ameliorating latitudinal gradients in temperature than in mangroves, where they are a secondary ecosystem engineer living under the mangrove canopy. On rocky shores, the enhancement of invertebrate abundance in oysters as compared to bare microhabitat decreased with latitude, as the maximum temperatures experienced by intertidal organisms diminished. By contrast, in mangrove forests, where the mangrove canopy resulted in maximum temperatures that were cooler and of greater humidity than on rocky shores, we found no evidence of latitudinal gradients of oyster effects on invertebrate abundance. Contrary to predictions, the magnitude by which oysters enhanced biodiversity was in many instances similar between mangroves and rocky shores. Whether habitat-context modifies patterns of spatial variation in the effects of ecosystem engineers on community structure will depend, in part, on the extent to which the environmental amelioration provided by an ecosystem engineer replicates that of other co-occurring ecosystem engineers.
Article
Model-based methods have emerged as a powerful approach for analysing multivariate abundance data in community ecology. Key applications include model-based ordination, modelling the various sources of correlations across species, and making inferences while accounting for these between species correlations. boral (version 0.9.1, licence GPL-2) is an r package available on cran for model-based analysis of multivariate abundance data, with estimation performed using Bayesian Markov chain Monte Carlo methods. A key feature of the boral package is the ability to incorporate latent variables as a parsimonious method of modelling between species correlation. Pure latent variable models offer a model-based approach to unconstrained ordination, for visualizing sites and the indicator species characterizing them on a low-dimensional plot. Correlated response models consist of fitting generalized linear models to each species, while including latent variables to account for residual correlation between species, for example, due to unmeasured covariates. © 2015 The Author. Methods in Ecology and Evolution
Article
Complexity is well accepted as one of the primary drivers of biodiversity, however, empirical support for such positive associations is often confounded with surface area and undermined by other potential explanatory factors, especially the type of structural component (e.g., pits, crevices, overhangs, etc.). In the present study, sample units (artificial substrates) of equal surface area (±0.2%) were used to simultaneously examine the independent effects of complexity and different structural component types on species richness (S), abundance (N), and community composition. We created simple and complex concrete substrates of four different geometric designs using novel software. The substrates (n = 8) were mounted onto granite seawalls (at two tidal heights) on two islands south of Singapore Island. After 13 months of colonization, all 384 tiles were collected and their assemblages compared. A total of 53 744 individuals of 70 species/morphospecies were collected and identified. Our results show that greater complexity can support greater species richness and different communities that are independent of surface area. Furthermore, the type of structure (e.g., "pits," "grooves," "towers") can have an effect on richness and community composition that is independent of complexity.
Article
AimThe global sprawl of marine hard infrastructure (e.g. breakwaters, sea walls and jetties) can extensively modify coastal seascapes, but the knowledge of such impacts remains limited to local scales. We examined the regional-scale effects of marine artificial habitats on the distribution and abundance of assemblages of ascidians, a key group of ecosystem engineer species in benthic fouling systems.LocationFive hundred kilometers of coastline in the North Adriatic Sea.Methods We sampled a variety of natural reefs, marine infrastructures and marinas, and tested hypotheses about the role of habitat type and location in influencing the relative distribution and abundance of both native and non-indigenous species.ResultsAssemblages differed significantly between natural and artificial habitats and among different types of artificial habitats. Non-indigenous species were 2–3 times more abundant on infrastructures built along sedimentary coastlines than on natural rocky reefs or infrastructures built close to rocky coastlines. Conversely, native species were twice as abundant on natural reefs than on nearby infrastructures and were scarce to virtually absent on infrastructures built along sedimentary coasts. The species composition of assemblages in artificial habitats was more similar to that of marinas than of natural reefs, independently of their location.Main conclusionsOur results show that marine infrastructures along sandy shores disproportionally favour non-indigenous over native hard bottom species, affecting their spread at regional scales. This is particularly concerning for coastal areas that have low natural densities of rocky reef habitats. We discuss design and management options to improve the quality as habitat of marine infrastructures and to favour their preferential use by native species over non-indigenous ones.
Article
behavior , site selection, keeps limpets well within vertical ranges dictated by physical tolerances. Critiques exisiting zonation paradigm.
Article
Ecologists have had little success in the development of a synthetic understanding of the effects of habitat structure on species, because structural complexity is measured differently in most studies and habitats. There were 3 main objectives of this study: (1) to measure and compare structural complexity between rocky intertidal and mangrove habitats, (2) to examine whether structural complexity affected the density, richness and size of gastropods in these habitats, and (3) to determine whether one index of structural complexity [e.g. fractal dimension (D) and chain-and-tape] best represented features of the habitat that affected gastropods. I used photogrammetric techniques to measure and to compare the effects of structural complexity in quadrats (1 m apart) nested within sites (10 m apart), shores (>1 km apart) and habitats (rocky intertidal and mangrove) in Botany Bay, Australia. All indices showed that complexity was different between quadrats just meters apart in both habitats and was greater in mangrove than in rocky intertidal habitats. Two lines of evidence indicated that variation in complexity affected the density of gastropods in rocky intertidal but not in mangrove habitats. First, the density of gastropods varied 4-fold between quadrats within habitats and, after gastropods were experimentally removed, a similar density and size distribution of gastropods recolonized quadrats in the rocky intertidal. Second, this density was correlated with structural complexity. D was most often correlated with density and thus best represented features of the habitat that affected gastropods. The measurement and effects of structural complexity can be compared between habitats, and these comparisons help elucidate the conditions in which habitat structure may exert strong effects on species.
Article
Individuals should exploit a spatially variable environment so as to increase their Darwinian fitness. Predators should aggregate in patches with relatively high densities of high-quality prey, and prey should in turn seek refuges providing protection from predators. This paper explores some of the consequences of such behavior for the coexistence of prey species in a patchy environment. It is argued that an aggregative predator response can lead to indirect interactions among otherwise non-interacting prey species co-occurring in a patch. In many circumstances, the interaction should be (-,-) (apparent competition), although in some situations other interactions may occur. If refuges are in short supply, then prey may compete for occupancy of refuges. Several models of such competition are presented. If predators act as density-independent mortality agents on prey outside refuges, it is shown for a simple model that two prey species cannot coexist when competing for a single refuge. Coexistence may be permitted if: (1) each prey has an exclusive refuge, (2) the dominant prey species experiences strong intraspecific interference, (3) there are trade-offs in competitive ability for refuges and for food resources, (4) the predator has a numerical response, and the prey that is subordinate in competition for refuge can better withstand predation (i.e., is superior in apparent competition). These models highlight the potential importance of spatial heterogeneity for understanding prey community structure.
Article
The algal flora was sampled in 15 intertidal rock pools, selected for habitat uniformity within a limited area. The distribution of species agreed closely with that expected at random, whether examined by the distribution of associations, by nesting, by chequerboarding or by incidence functions. The simplest explanation is that differences in specific composition between the pools are caused by chance.
Article
Glass's estimator of effect size, the sample mean difference divided by the sample standard deviation, is studied in the context of an explicit statistical model. The exact distribution of Glass's estimator is obtained and the estimator is shown to have a small sample bias. The minimum variance unbiased estimator is obtained and shown to have uniformly smaller variance than Glass's (biased) estimator. Measurement error is shown to attenuate estimates of effect size and a correction is given. The effects of measurement invalidity are discussed. Expressions for weights that yield the most precise weighted estimate of effect size are also derived.
Article
Light compensation points (I(c)) for growth were low (0.3 to 2.5 mumol m-2 s-1) for the temperate marine macroalgae Chondrus crispus, Fucus serratus, Petalonia fascia, Porphyra purpurea and Ulva lactuca measured at 7-degrees-C. These I(c)-values corresponded to those estimated by a physiological model including light absorption and quantum yield for growth to describe carbon gain, and weight specific dark respiration, dark loss rate and thallus specific carbon (mol C m-2 thallus) to describe carbon loss. Absorption and quantum yield were close to the theoretical maximum for all species and could not explain differences in I(c). Respiration and thallus specific carbon varied more than 15-fold and were the main factors responsible for variations in I(c). Experimental I(c)-values correspond to 0.12 to 0.61 % of the yearly surface light dose in Denmark (56-degrees-N). These values agree with the % of surface light (%SI) available at the depth limits of leathery and foliose macroalgae at different latitudes. Hence, there is no surplus of energy to balance grazing and mechanical losses, and these factors must be of minor importance for macroalgae growing at great depths. A literature review of depth limits for marine macroalgae reveals an upper zone of mainly leathery algae with depth limits of about 0.5 % SI, an intermediate zone of foliose and delicate algae with depth limits at about 0.10 % SI, and a lower zone of encrusted algae extending down to about 0.01 % SI. This zonation pattern is accompanied by a decrease in thallus specific carbon (i.e. thinner thalli) with increasing depth. The inverse relationship between growth rate at low light and thallus specific carbon suggests that a thin thallus is essential for growth and survival of marine macroalgae at great depths.