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Abstract

Nutrient pollution and reduced grazing each can stimulate algal blooms as shown by numerous experiments. But because experiments rarely incorporate natural variation in environmental factors and biodiversity, conditions determining the relative strength of bottom-up and top-down forcing remain unresolved. We factorially added nutrients and reduced grazing at 15 sites across the range of the marine foundation species eelgrass (Zostera marina) to quantify how top-down and bottom-up control interact with natural gradients in biodiversity and environmental forcing. Experiments confirmed modest top-down control of algae, whereas fertilisation had no general effect. Unexpectedly, grazer and algal biomass were better predicted by cross-site variation in grazer and eelgrass diversity than by global environmental gradients. Moreover, these large-scale patterns corresponded strikingly with prior small-scale experiments. Our results link global and local evidence that biodiversity and top-down control strongly influence functioning of threatened seagrass ecosystems, and suggest that biodiversity is comparably important to global change stressors. © 2015 John Wiley & Sons Ltd/CNRS.

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... However, a remaining major challenge is to understand to what extent their individual or combined roles shape community structure and trophic networks in different key habitats. Seagrass ecosystems have emerged as a model system for testing the relative importance of bottom-up and top-down forcing in marine environments (e.g., Whalen et al. 2013;Duffy et al. 2015;Yan et al. 2020). ...
... Despite evidence from correlative studies supporting a negative impact of nutrient addition on seagrass (Hughes et al. 2004), many nutrient addition experiments have failed to demonstrate significant effects in the field despite substantial increases in local nutrient concentrations (e.g., Ruckelshaus 1993, Heck et al. 2000;Baden et al. 2010), suggesting the importance of context-dependency. Nutrient dilution effects due to hydrodynamic settings, experimental design, and/or rapid grazing of epiphytes which transfer nutrients into mesograzers biomass, may all contribute to the difficulty in detecting bottom-up forcing (Baden et al. 2010;Reynolds et al. 2014;Duffy et al. 2015). Thus, concurrent experimental manipulations of bottom-up and top-down processes is critical for a mechanistic understanding of the effects of anthropogenic drivers on a given seagrass ecosystem. ...
... The experimental setup was based on standardized protocols developed within the Zostera Experimental Network (www.zenscience.org), described in detail in Duffy et al. (2015). Prior to that global study, the methods (experimental duration, nutrient fertilization, mesograzer deterrence) were tested in detail in a pilot study (Whalen et al. 2013). ...
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Understanding the ecological interactions that enhance the resilience of threatened ecosystems is essential in assuring their conservation and restoration. Top‐down trophic interactions can increase resilience to bottom‐up nutrient enrichment, however, as many seagrass ecosystems are threatened by both eutrophication and trophic modifications, understanding how these processes interact is important. Using a combination of approaches, we explored how bottom‐up and top‐down processes, acting individually or in conjunction, can affect eelgrass meadows and associated communities in the northern Baltic Sea. Field surveys along with fish diet and stable isotope analyses revealed that the eelgrass trophic network included two main top predatory fish species, each of which feeds on a separate group of invertebrate mesograzers (crustaceans or gastropods). Mesograzer abundance in the study area was high, and capable of mitigating the effects of increased algal biomass that resulted from experimental nutrient enrichment in the field. When crustacean mesograzers were experimentally excluded, gastropod mesograzers were able to compensate and limit the effects of nutrient enrichment on eelgrass biomass and growth. Our results suggest that top‐down processes (i.e., suppression of algae by different mesograzer groups) may ensure eelgrass resilience to nutrient enrichment in the northern Baltic Sea, and the existence of multiple trophic pathways can provide additional resilience in the face of trophic modifications. However, the future resilience of these meadows is likely threatened by additional local stressors and global environmental change. Understanding the trophic links and interactions that ensure resilience is essential for managing and conserving these important ecosystems and the services they provide.
... More generally, the top-down effects of invertebrate grazers or 'epifauna' in seagrass communities have been well described around the world (reviewed by Heck and Valentine 2007) and indicate that on average top-down forces are stronger than bottomup forces (Hughes et al. 2004). This pattern appears relatively generalizable across large spatial scales, however, community composition and environmental conditions can differ greatly at the local scale, which can modulate the importance of topdown versus bottom-up (Duffy et al. 2015). ...
... Our hypotheses were based on trophic cascade theory, documented trophic cascades in the northeast Atlantic and Elkhorn Slough, CA, and sea otter foraging ecology in southeast Alaska and focused on direct relationships between variables. Specifically we hypothesized that sea otters would have a negative relationship with crab biomass (Hoyt 2015), crab and fish biomass would have a negative relationship with epifauna load (Moksnes et al. 2008, Baden et al. 2010, Lewis and Anderson 2012, Hughes et al. 2013, epifauna load would have a negative relationship with macroalgae cover, diatom cover and epiphyte load, and epiphyte load would have a negative relationship with seagrass biomass (Hughes et al. 2004, Heck and Valentine 2007, Jephson et al. 2008, Duffy et al. 2015. We also hypothesized that the bottom-up forces of light and water nitrate concentration would have a positive relationship with both seagrass biomass and epiphyte load . ...
... We found evidence for some of the hypothesized ecological relationships indicative of a trophic cascade but they varied in their strength of evidence. This included many of the direct relationships among environmental variables-seagrass-epiphyte-epifauna portion of the community, consistent with numerous trophic seagrass studies (reviewed by Hughes et al. 2004) and to other large scale studies (Duffy et al. 2015). However, the strength of evidence for these relationships varied. ...
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The presence and strength of trophic cascades can be a function of the local abiotic environment and relative abundance of key species. The reintroduction and expansion of sea otters Enhydra lutris, a known keystone species in kelp ecosystems, in southeast Alaska provides a rare natural experiment to test the generality of a apex-predator-seagrass trophic cascades across a broad spatial scale. We conducted an in-depth sea-grass community survey at 21 sites spanning ~100 km with variable sea otter presence to test for patterns of alternating abundance and direct relationships between species indicative of trophic cascades. Our analysis revealed some of the trophic relationships predicted by the apex predator-seagrass trophic cascades theory, including a strong negative relationship between sea otters and crabs and many of the expected relationships between nitrate, seagrass, epiphytes and epifauna. Other expected relationships within a trophic cascade, however, were not supported-including no relationship between crabs and epifauna, a critical link in the trophic cascade. Given the lack of evidence for all hypothesized direct relationships, we conclude that a sea otter mediated trophic cascade may not be present in southeast Alaska and could be due to local scale factors including the spatial heterogeneity, low resource availability and non-linear food chains in southeast Alaska seagrass communities. However, correlation analyses suggest further interactions among biological and environmental variables in southeast Alaska seagrass communities, including a positive correlation between sea otters and seagrass biomass. These results suggest that the effects of recovering apex-predator populations may not be generalizable across regions and spatial scales, highlighting a need for local assessment on the ecology and management of these populations.
... Eelgrass (Zostera marina) is a species of seagrass that occurs in the intertidal to subtidal areas of coasts, estuaries, and lagoons in the Northern Hemisphere and forms a dense meadow, called the eelgrass bed, in sandy or muddy sea bottoms (Duffy et al. 2015). Eelgrass beds support the biodiversity in the coastal environment by hosting a wide variety of plants and animal species. ...
... Eelgrass beds support the biodiversity in the coastal environment by hosting a wide variety of plants and animal species. Both plant-plant and plant-animal interactions are important in determining community structure (Duffy et al. 2015). Aside from eelgrass, various macroalgae and microalgae attach to the aboveground part of eelgrass (Momota and Nakaoka 2017). ...
... Epiphytic microalgae and eelgrass often compete for light resources, and there is a negative effect of overgrown epiphytic algae on the photosynthetic activities of eelgrass (Hauxwell et al. 2003). Grazing herbivores (hereafter grazers), such as sea urchins and waterfowl, feed on eelgrass directly, while grazers, such as amphipods and gastropods, feed on epiphytic microalgae or both eelgrass and microalgae (Duffy et al. 2015). Direct feeding of eelgrass can have a negative impact on eelgrass growth and biomass, while feeding of epiphytic microalgae would have an indirect positive effect on eelgrass , Whalen et al. 2013). ...
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Understanding biological community responses to disturbances such as extreme rainfalls under climate change is crucial when predicting ecosystem changes and functions. However, it is still unclear how species interaction changes with increasing disturbances and how disturbance susceptibility varies among organisms from habitats with different stress levels along stress gradients such as salinity gradients. We examined whether (1) higher frequency (i.e., pulse disturbance) and longer duration (i.e., press disturbance) of salinity change affected the primary producers, animals, and their interactions, and whether (2) organisms from naturally stressful habitats with unstable salinity were more tolerant to salinity changes. We used eelgrass Zostera marina, epiphytic microalgae, and grazer gastropod Lacuna decorata from two sites in each of the two lagoons; Akkeshi with a strong salinity gradient, and Notoro with a weak gradient to do indoor mesocosm experiments for testing the effects of salinity change and grazer presence on eelgrass growth and biomass of epiphytic microalgae, as well as grazer survival, growth, and consumption rates. We established treatments with low, intermediate, and high levels of salinity stress to test the effects of press and pulse disturbances in terms of salinity changes. The findings suggest the presence of a top‐down control of epiphytic microalgae by grazers. Eelgrass growth rate was higher with the presence of grazers but declined with higher salinity stress. The biomass of epiphytic microalgae was higher with the absence of grazers and with higher salinity stress across all sites. Grazer survival varied among individuals raised in habitats with naturally stable or unstable salinity regime and decreased with more frequent and longer salinity changes. Grazer growth rates and grazing rates also decreased with higher salinity stress, but grazing on epiphytic microalgae was highest at the intermediate stress levels across all sites. This study demonstrates that salinity regime shifts that are expected to occur with extreme rainfalls due to ongoing climate change could affect coastal ecosystems such as eelgrass beds, and we call for further investigations on the different stress responses of organisms raised in habitats with stable and unstable salinity to understand the potential effects of the disturbances on ecosystem function.
... Algal grazing by mesograzer communities within seagrass meadows is an important function, providing a key link in trophic energy transfer within seagrass ecosystems and buffering negative effects to seagrasses associated with eutrophication and an overabundant epiphytic algae community [18,19]. For example, in eutrophication experiments, ambient grazing pressures associated with mesograzers promoted increases in both seagrass and grazer biomass [17,18]. ...
... For example, in eutrophication experiments, ambient grazing pressures associated with mesograzers promoted increases in both seagrass and grazer biomass [17,18]. However, when mesograzer abundance was reduced, algal dominance increased and seagrass abundance and biomass declined [18][19][20]. Mesograzer abundance alone may be inadequate to fully characterise the observed process. Richness within grazer communities, primarily in gastropod and amphipod taxa, was also shown to increase the efficiency of grazer consumption [19,21,22]. ...
... Mesograzer abundance alone may be inadequate to fully characterise the observed process. Richness within grazer communities, primarily in gastropod and amphipod taxa, was also shown to increase the efficiency of grazer consumption [19,21,22]. Previous experimental work regarding these systems also demonstrated an effect from primary diversity, whereby seagrass plots with higher genotypic richness recruited more abundant invertebrate communities and more diverse grazing communities were more effective at consuming epiphytic algae [23][24][25][26]. ...
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Consumer communities play an important role in maintaining ecosystem structure and function. In seagrass systems, algal regulation by mesograzers provides a critical maintenance function which promotes seagrass productivity. Consumer communities also represent a key link in trophic energy transfer and buffer negative effects to seagrasses associated with eutrophication. Such interactions are well documented in the literature regarding temperate systems, however, it is not clear if the same relationships exist in tropical systems. This study aimed to identify if the invertebrate communities within a tropical, multispecies seagrass meadow moderated epiphyte abundance under natural conditions by comparing algal abundance across two sites at Green Island, Australia. At each site, paired plots were established where invertebrate assemblages were perturbed via insecticide manipulation and compared to unmanipulated plots. An 89% increase in epiphyte abundance was seen after six weeks of experimental invertebrate reductions within the system. Using generalised linear mixed-effect models and path analysis, we found that the abundance of invertebrates was negatively correlated with epiphyte load on seagrass leaves. Habitat species richness was seen to be positively correlated with invertebrate abundance. These findings mirrored those of temperate systems, suggesting this mechanism operates similarly across latitudinal gradients.
... Like many aquatic macrophyte foundation species, seagrasses form meadows that host vast biodiversity of algae, invertebrates and fish (Boström et al., 2006b,a;Duffy, 2006;Duffy et al., 2015;Whippo et al., 2018). Seagrass-epiphyte interactions are central to seagrass ecosystems and can be competitive for nutrients and light (Hauxwell et al., 1998;McGlathery, 2001) or a symbiotic relationship mediated by nutrient exchange (Harlin, 1973a). ...
... Seagrass-epiphyte interactions are central to seagrass ecosystems and can be competitive for nutrients and light (Hauxwell et al., 1998;McGlathery, 2001) or a symbiotic relationship mediated by nutrient exchange (Harlin, 1973a). In addition to their interactions with seagrass, epiphytic algae also play an important role at the base of the green food web associated with seagrass habitats in temperate systems (Duffy et al., 2015;Fry, 1984;Reynolds et al., 2014). Understanding causes of variation in epiphyte abundance, and seagrass-epiphyte interactions, is an important component of understanding energy flow and community structure of a seagrass meadow (Heck et al., 2000;McGlathery, 2001). ...
... In coastal habitats of the northeast Pacific Ocean, the meadowforming seagrass Zostera marina (hereafter, Zostera) provides food and habitat for a diverse assemblage of invertebrates and fish (Duffy et al., 2015;Huang et al., 2015;Stark et al., 2020;Whippo et al., 2018), and consequently is considered an ecologically and economically important foundation species (Department of Fisheries and Oceans DFO Canada, 2009). One of the most striking macroalgae present on seagrass in this region is the red algae Smithora naiadum (hereafter Smithora), also known as seagrass laver, which can grow in abundance on Zostera (Fig. 1A). ...
Article
In aquatic foundation species, composition and abundance of associated epibionts can change substantially over small spatial distances. Such spatial variation can reflect top-down control by consumers, bottom-up control by abiotic factors or facilitation, or a combination of processes. We used visual and molecular surveys to describe spatial patterns in the abundance and distribution of the epiphytic red macroalga Smithora naiadum in a meadow of the seagrass Zostera marina on the Central Coast of British Columbia. We detected Smithora using 18 S ribosomal RNA molecular marker throughout the seagrass meadow at both interior and edge sites, even in the absence of macroscopic Smithora. We used a reciprocal transplant experiment to test two hypotheses: that patterns in Smithora abundance reflect local environmental conditions, or alternately, that patterns reflect spatial variation in the host plant attributes, microbiota and grazers. Zostera shoots hosted more Smithora at meadow edges relative to meadow interior sites, and shoots with Smithora were associated with distinct invertebrate grazer and bacterial communities relative to shoots 5 m in from the meadow edge without Smithora. Macroscopic Smithora grew on shoots experimentally transplanted from the interior to the meadow edge and shoots hosting Smithora that were transplanted to the interior did not lose Smithora. Our survey and experimental results suggest that presence of macroscopic Smithora blades on Zostera shoots changes the Zostera microbiota. Altogether, we conclude that environmental variation, not host plant attributes or dispersal limitation, affects Smithora colonization on Zostera, and once established, Smithora alters the microbiota on Zostera.
... We sampled adult fish during spawning in spring (May), and young-of-the-year juveniles in late summer (August). Using path analysis to tease apart direct and indirect relationships 48 , we then compared the fit of 14 multivariate hypotheses of the direct and indirect drivers of perch and stickleback recruitment, as graphical network models of interacting paths 36,49 (see "Methods" and Supplementary Table 2 for details). ...
... Importance of predator-prey reversal for fish recruitment. To assess the relative importance of predation and predator-prey reversal for juvenile fish recruitment, we combined an ecosystem field survey with causal path analysis; a powerful approach to tease apart the role of direct and indirect interactions in ecosystems 36,49 . In 2014, we surveyed 32 shallow bays (<3.5 m depth) situated >10 km apart (or separated by natural fish movement barriers like deep water or land) along a 360 km stretch of the central Swedish Baltic Sea coast ( Supplementary Fig. 5). ...
... Based on ecological knowledge of the study system, we expressed 14 multivariate hypotheses of the direct and indirect drivers of perch and stickleback recruitment, as graphical network models of interacting paths 36,49 . Due to the relatively low sample size we restricted the number of paths to 7. The two simplest models assumed that perch+pike and stickleback juvenile abundance in summer (i.e. ...
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Regime shifts in ecosystem structure and processes are typically studied from a temporal perspective. Yet, theory predicts that in large ecosystems with environmental gradients, shifts should start locally and gradually spread through space. Here we empirically document a spatially propagating shift in the trophic structure of a large aquatic ecosystem, from dominance of large predatory fish (perch, pike) to the small prey fish, the three-spined stickleback. Fish surveys in 486 shallow bays along the 1200 km western Baltic Sea coast during 1979–2017 show that the shift started in wave-exposed archipelago areas near the open sea, but gradually spread towards the wave-sheltered mainland coast. Ecosystem surveys in 32 bays in 2014 show that stickleback predation on juvenile predators (predator–prey reversal) generates a feedback mechanism that appears to reinforce the shift. In summary, managers must account for spatial heterogeneity and dispersal to better predict, detect and confront regime shifts within large ecosystems.
... The current global decline in biodiversity at an unprecedented rate because of human actions (Barnosky et al. 2011) has prompted many studies to test how biodiversity influences the ecosystem functioning. These studies have found evidence that more diverse communities sustain higher ecosystem functioning, i.e., more ecosystem functions are maximized simultaneously (Maestre et al. 2012;Cardinale et al. 2012;Duffy et al. 2015). For instance, diverse communities may simultaneously sustain more efficient nutrient cycling and higher biomass production compared to less diverse communities Ritchie 2001, 2002). ...
... The COM effect has been noted as the main overyielding mechanism by which diverse communities produce more biomass than less diverse communities (Loreau and Hector 2001;Loreau and Mazancourt 2013;Isbell et al. 2015). Although there have been great advances in the understanding of ecosystem functioning and stability in the last 20 years (e.g., Tilman et al. 2006;Maestre et al. 2012;Duffy et al. 2015;Graven et al. 2018), there is still little empirical evidence regarding these key processes operate in nature. Moreover, we know relatively little about how overyielding effects occur in aquatic communities, especially in the tropics where these types of studies are scarce (but see Riis et al. 2018;Moi et al. 2021;Wu et al. 2021). ...
Article
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Diverse communities are more productive than less diverse ones because of two overyielding mechanisms: a selection effect and a complementarity effect, which operate in different ways. Moreover, ecosystem multifunctionality is expected to increase and become more stable with increasing species diversity. However, it is unclear how the aforementioned processes operate in aquatic ecosystems, where the overyielding mechanisms, ecosystem multifunctionality, and stability have been poorly explored. Here, we conducted an experimental study manipulating three levels of macrophyte richness to test two hypotheses: (i) the positive macrophyte richness effect on community biomass production is the result of the species complementarity effect; (ii) ecosystem multifunctionality and its stability increase with macrophyte richness. We found that macrophyte species increased their biomass production in high richness treatment, evidencing overyielding, which occurred through a significant complementarity effect. Macrophyte richness also enhanced ecosystem multifunctionality, and made it more stable over time, but only in high richness treatment. Our study shows that preserving high macrophyte richness is essential to preserving the ability of aquatic communities and ecosystems to sustain their functioning.
... Numerous manipulative experiments have explored the combined effects of nutrient enrichment and herbivory as bottom-up and top-down controls on seagrass ecosystem. However, these experiments were mostly conducted in distinct natural habitats with wide-ranging varieties in latitude, trophic level, etc., occasionally leading to contrasting findings (Hughes et al., 2004;Duffy et al., 2015). For example, some studies showed that nutrient enrichment overrides top-down control on the shift of the dominant species from seagrass to algae (Hughes et al., 2004;Östman et al., 2016), while other studies revealed insignificant nutrient effects but strong top-down control on seagrass growth (Heck et al., 2000;Campbell et al., 2018). ...
... Regarding the environmental mediation of top-down and bottom-up controls on seagrass ecosystems, previous studies have revealed the importance of temperature as a mediating factor. For instance, Duffy et al. (2015) reported that similar to species richness, the effect of grazers controlling algae increased with temperature. Temperature-induced changes in the herbivore functional composition were further found to alter the relative importance of nutrients (Campbell et al., 2018). ...
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While nutrient enrichment and herbivory have been well recognized as the main driving factors of seagrass meadow fragmentation and degradation, there is limited understanding of how their relative importance shifts across large spatial scales where environmental factors such as turbidity can vary. In this study, a field control experiment was conducted in two Zostera japonica meadows distributed on the two banks of the Yellow River Estuary with different turbidity, to investigate the combined effects of nutrient enrichment and herbivory on seagrass and macroalgae. Our results showed that turbidity had the mediating force of shifting the relative importance of nutrient enrichment and herbivory to seagrass and macroalgae. While herbivory played a vital role in maintaining the balance between the two primary producers in a turbid environment, nutrient enrichment tended to offset herbivory-induced biomass loss by promoting seagrass growth in a less turbid system. Additionally, two potential mechanisms that might regulate the responses of seagrasses and macroalgae to nutrient enrichment and herbivory under different turbidity are proposed. On the one hand, turbidity might mediate the feeding preference of herbivores. On the other hand, nutrient enrichment favors the growth of opportunistic macroalgae over seagrass in turbid systems. Our study emphasizes the mediating force of turbidity on seagrass ecosystems, and provides references for the protection and restoration of seagrass meadows under multiple environmental stressors, and prompts further studies on the feedback between sediment dynamics and seagrass meadows in the context of ecogeomorphology.
... Several clades of seagrasses arose independently from freshwater sister taxa 3-4 times between the Paleocene and late Eocene (~65-34 mya) and are the only fully marine, flowering plants (~14 genera and~65 species) (Chase et al. 2016). They occur in predominantly soft-sediment, marine coastal environments worldwide (Green, Short, and Frederick 2003) and as engineering species provide the foundation of three-dimensional habitats that are among the most productive and biodiverse (Costanza et al. 1997;Duffy et al. 2015). Seagrass meadows provide numerous ecosystem services, e.g., provisioning of fish and invertebrates, retention of nutrients (Larkum, Orth, and Duarte 2006) and carbon sequestration (Fourqurean et al. 2012). ...
... Seagrass meadows provide numerous ecosystem services, e.g., provisioning of fish and invertebrates, retention of nutrients (Larkum, Orth, and Duarte 2006) and carbon sequestration (Fourqurean et al. 2012). Unfortunately, they are also under threat related to human impacts (Waycott et al. 2009) that fundamentally change coastal system dynamics (Duffy et al. 2015) and make restoration extremely difficult (van Katwijk et al. 2016). Effective marine conservation strategies require integrative research perspectives between ecology and genomics (Hillebrand, Jacob, and Leslie 2020) because ecological and evolutionary change can and do occur on the same time scales (Carroll et al. 2007), e.g., genetic polymorphisms underlying critical traits or the role of genetic diversity at selectively relevant sites for population resilience. ...
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Background: Seagrasses (Alismatales) are the only fully marine angiosperms. Zostera marina (eelgrass) plays a crucial role in the functioning of coastal marine ecosystems and global carbon sequestration. It is the most widely studied seagrass and has become a marine model system for exploring adaptation under rapid climate change. The original draft genome (v.1.0) of the seagrass Z . marina (L.) was based on a combination of Illumina mate-pair libraries and fosmid-ends. A total of 25.55 Gb of Illumina and 0.14 Gb of Sanger sequence was obtained representing 47.7× genomic coverage. The assembly resulted in ~2000 unordered scaffolds (L50 of 486 Kb), a final genome assembly size of 203MB, 20,450 protein coding genes and 63% TE content. Here, we present an upgraded chromosome-scale genome assembly and compare v.1.0 and the new v.3.1, reconfirming previous results from Olsen et al. (2016), as well as pointing out new findings. Methods: The same high molecular weight DNA used in the original sequencing of the Finnish clone was used. A high-quality reference genome was assembled with the MECAT assembly pipeline combining PacBio long-read sequencing and Hi-C scaffolding. Results: In total, 75.97 Gb PacBio data was produced. The final assembly comprises six pseudo-chromosomes and 304 unanchored scaffolds with a total length of 260.5Mb and an N50 of 34.6 MB, showing high contiguity and few gaps (~0.5%). 21,483 protein-encoding genes are annotated in this assembly, of which 20,665 (96.2%) obtained at least one functional assignment based on similarity to known proteins. Conclusions: As an important marine angiosperm, the improved Z. marina genome assembly will further assist evolutionary, ecological, and comparative genomics at the chromosome level. The new genome assembly will further our understanding into the structural and physiological adaptations from land to marine life.
... Indeed, increases in decomposition rates could have positive feedback effects on climate warming by enhancing C losses (Kirschbaum, 2000). The diversity of decomposers (invertebrates and microorganisms that fragment and decompose organic matter in both aquatic and terrestrial systems) is crucial for litter decomposition (Eisenhauer et al., 2012;García-Palacios et al., 2013;Gessner et al., 2010;Handa et al., 2014;Hättenschwiler et al., 2005) and for other ecosystem functions as well (Eisenhauer et al., 2019a;Lefcheck et al., 2015;Schuldt et al., 2018). Despite the importance of decomposers, BEF experiments focusing on litter decomposition more often addressed the influence of plant litter diversity than of decomposers (Gessner et al., 2010;Tonin et al., 2018). ...
... lower than two units) than the SEM including the biodiversity path. Residuals from the two sub-models of each SEM were graphically evaluated for strong departure to normality and relationship with the fitted values (Duffy et al., 2015). For these analyses, we averaged the residuals across data resampling iterations for each observation. ...
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Understanding the consequences of ongoing biodiversity changes for ecosystems is a pressing challenge. Controlled biodiversity-ecosystem function experiments with random biodiversity loss scenarios have demonstrated that more diverse communities usually provide higher levels of ecosystem functioning. However, it is not clear if these results predict the ecosystem consequences of environmental changes that cause non-random alterations in biodiversity and community composition. We synthesized 69 independent studies reporting 660 observations of the impacts of two pervasive drivers of global change (chemical stressors and nutrient enrichment) on animal and microbial decomposer diversity and litter decomposition. Using meta-analysis and structural equation modeling, we show that declines in decomposer diversity and abundance explain reduced litter decomposition in response to stressors but not to nutrients. While chemical stressors generally reduced biodiversity and ecosystem functioning, detrimental effects of nutrients occurred only at high levels of nutrient inputs. Thus, more intense environmental change does not always result in stronger responses, illustrating the complexity of ecosystem consequences of biodiversity change. Overall, these findings provide strong evidence that the consequences of observed biodiversity change for ecosystems depend on the kind of environmental change, and are especially significant when human activities decrease biodiversity.
... The diet differences were caused by one prey group only: completely plated sticklebacks more often consumed amphipods. Amphipods are important benthic herbivores in the area (Eriksson et al. 2009, Sieben et al. 2011b, and they form a key grazer group that mediate cascading ecosystem effects in coastal areas across the world (Duffy and Hay 2000, R aberg and Kautsky 2007, Moksnes et al. 2008, Duffy et al. 2015, Donadi et al. 2017. We have no indication as to why completely plated stickleback ate more amphipods than the partially plated individuals. ...
... The hypothesis of an eco-evolutionary feedback in the Baltic Sea is partly supported by our results: The number and proportion of incompletely plated stickleback increased with production in bays with low abundances of perch, indicating a reduced selection for antipredator traits and increased density-dependent selection when larger predators of stickleback decrease. We also found small but significant differences in diets between the phenotypes, where the incompletely plated individuals consumed less amphipods; which is a key benthic herbivore regulating trophic transfer between predators and algae in many shallow marine systems across the world (e.g., Duffy and Hay 2000, Moksnes et al. 2008, Duffy et al. 2015, Donadi et al. 2017. However, to provide solid empirical predictions of eco-evolutionary consequences of the shift in selection pressures, we need experimental testing of the ecological effects of different phenotypes, behavioral studies to assess v www.esajournals.org ...
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Declines of large predatory fish due to overexploitation are restructuring food webs across the globe. It is now becoming evident that restoring these altered food webs requires addressing not only ecological processes, but evolutionary ones as well, because human‐induced rapid evolution may in turn affect ecological dynamics. We studied the potential for niche differentiation between different plate armor phenotypes in a rapidly expanding population of a small prey fish, the three‐spined stickleback (Gasterosteus aculeatus). In the central Baltic Sea, three‐spined stickleback abundance has increased dramatically during the past decades. The increase in this typical mesopredator has restructured near‐shore food webs, increased filamentous algal blooms, and threatens coastal biodiversity. Time‐series data covering 22 years show that the increase coincides with a decline in the number of juvenile perch (Perca fluviatilis), the most abundant predator of stickleback along the coast. We investigated the distribution of different stickleback plate armor phenotypes depending on latitude, environmental conditions, predator and prey abundances, nutrients, and benthic production; and described the stomach content of the stickleback phenotypes using metabarcoding. We found two distinct lateral armor plate phenotypes of stickleback, incompletely and completely plated. The proportion of incompletely plated individuals increased with increasing benthic production and decreasing abundances of adult perch. Metabarcoding showed that the stomach content of the completely plated individuals more often contained invertebrate herbivores (amphipods) than the incompletely plated ones. Since armor plates are defense structures favored by natural selection in the presence of fish predators, the phenotype distribution suggests that a novel low‐predation regime favors stickleback with less armor. Our results suggest that morphological differentiation of the three‐spined stickleback has the potential to affect food web dynamics and influence the persistence and resilience of the stickleback take‐over in the Baltic Sea.
... Fishes are key components of seagrass ecosystems, which can directly promote healthy habitats by deterring herbivores (Eger & Baum, 2020) or indirectly promote grazers of epiphytic algae colonizing seagrass blades (Moksnes et al., 2008); their secondary production also feeds higher trophic levels that support commercial fisheries (Unsworth et al., 2019). Despite their global distribution and contribution to fisheries, few studies have examined BEF mechanisms in seagrass ecosystems (Allgeier et al., 2015;Duffy et al., 2015), particularly for fish communities. Thus, while there is evidence that genetic diversity within some seagrasses can promote productivity and stability (Abbott et al., 2017;Hughes & Stachowicz, 2004), as can species diversity in invertebrates, such as snails and crustaceans (Duffy et al., 2015), we know much less about the mechanisms driving secondary production in the diverse fish communities found in seagrasses. ...
... Despite their global distribution and contribution to fisheries, few studies have examined BEF mechanisms in seagrass ecosystems (Allgeier et al., 2015;Duffy et al., 2015), particularly for fish communities. Thus, while there is evidence that genetic diversity within some seagrasses can promote productivity and stability (Abbott et al., 2017;Hughes & Stachowicz, 2004), as can species diversity in invertebrates, such as snails and crustaceans (Duffy et al., 2015), we know much less about the mechanisms driving secondary production in the diverse fish communities found in seagrasses. ...
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Biodiversity and ecosystem function are often correlated, but there are multiple hypotheses about the mechanisms underlying this relationship. Ecosystem functions such as primary or secondary production may be maximized by species richness, evenness in species abundances, or the presence or dominance of species with certain traits. Here, we combine surveys of natural fish communities (conducted in July and August 2016) with morphological trait data to examine relationships between biodiversity and ecosystem function (quantified as fish community biomass) across 14 subtidal eelgrass meadows in the Northeast Pacific (54°N, 130°W). We employ both taxonomic and functional trait measures of diversity to investigate whether ecosystem function is best predicted by species diversity (complementarity hypothesis) or by the presence or dominance of species with particular trait values (selection or dominance hypotheses). After controlling for environmental variation, we find that fish community biomass is maximized when taxonomic richness and functional evenness are low, and in communities dominated by species with particular trait values, specifically those associated with benthic habitats and prey capture. While previous work on fish communities has found that species richness is often positively correlated with ecosystem function, our results instead highlight the capacity for regionally prevalent and locally dominant species to drive ecosystem function in moderately diverse communities. We discuss these alternate links between community composition and ecosystem function and consider their divergent implications for ecosystem valuation and conservation prioritization. We tested whether more fish species living in seagrass meadows in northern Canada was related to the function of that ecosystem. Instead of more species equally more functioning, we found that dominant species were the most important factor.
... for manipulations in grasslands and seagrass meadows, respectively. Results from such networks allow both, examination of specific results from single-site studies and of generalized patterns across geographically distant field sites (Adler et al. 2011;Duffy et al. 2015). Similar projects have also been implemented in lake ecosystems based on collaborative research projects (Stephen et al. 2004;Mahdy et al. 2015). ...
... The second is that researchers are forced to synthesize knowledge from uncoordinated, context-specific studies performed in very different experimental facilities (Benton et al. 2007). Over recent years, there has been a shift towards experimental standardization and replicability, including equipment (e.g., mesocosm type), experimental set-up and sampling procedures across multiple sites, to achieve generality (e.g., Kemp et al. 2009;Borer et al. 2014;Duffy et al. 2015). However, bottom-up consortia of already established experimental facilities linked to individual research units has clearly dominated this development. ...
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For aquatic scientists mesocosm experiments are important tools for hypothesis testing as they offer a compromise between experimental control and realism. Here we present a new mesocosm infrastructure—SITES AquaNET—located in five lakes connected to field stations in Sweden that cover a ~760 km latitudinal gradient. SITES AquaNet overcomes major hindrances in aquatic experimental research through: (i) openness to the scientific community, (ii) the potential to implement coordinated experiments across sites and time, and (iii) high‐frequency measurements (temperature, photosynthetic photon flux density, turbidity and dissolved oxygen, chlorophyll a and phycocyanin concentrations) with an autonomous sensor system. Moreover, the infrastructure provides operational guidance and sensor expertise from technical staff, and connections to a multi‐layered monitoring programme (“SITES Water”) for each lake. This enables ecological observations from whole lake ecosystems to be compared with experimental studies aiming at disentangling major drivers and mechanisms underlying observed changes. Here we describe the technical properties of the infrastructure along with possibilities for experimental manipulations to tackle pressing issues in aquatic ecology and global change science. As a proof of concept, we also present a first mesocosm experiment across all five field sites with a cross‐factorial design to evaluate responses of the sensor measurements to press/bottom‐up (constant light reduction) and pulse/top‐down (temporary fish predation) disturbances. This demonstrates the suitability of the infrastructure and autonomous sensor system to host modularized experiments and exemplifies the power and advantages of the approach to integrate a network of mecsocosm facilities with manageable costs across large geographic areas.
... Seagrasses are marine flowering plants that form structurally complex and highly productive habitats in coastal areas worldwide (Hemminga and Duarte 2008). Seagrass meadows provide valuable ecosystem functions and services, including sediment stabilization, carbon storage, and critical habitat for a range of marine species (Barbier et al. 2011;Duffy et al. 2015); therefore, they are a focus for protection and management around the world (DFO 2009a;Marion and Orth 2010;Unsworth et al. 2019). Despite their ecological and economic significance, seagrass meadows face numerous threats associated with coastal development, pollution, aquaculture, invasive species, and fisheries practices (Orth et al. 2006;Murphy et al. 2019). ...
... FACETS | 2021 | 6: 139-179 | DOI: 10.1139/facets-2020-0020 155 facetsjournal.com Still, observations suggest that eelgrass can grow in salinities as low as 5 PSU (Duffy et al. 2015) and there is evidence that eelgrass populations can adapt to lower salinity conditions, although this can cause changes in morphology, density, and at very low salinities, reductions in reproduction and subsequent mortality ). ...
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Seagrass meadows are among the most productive and diverse marine ecosystems, providing essential structure, functions, and services. They are also among the most impacted by human activities and in urgent need of better management and protection. In Canada, eelgrass ( Zostera marina) meadows are found along the Atlantic, Pacific, and Arctic coasts, and thus occur across a wide range of biogeographic conditions. Here, we synthesize knowledge of eelgrass ecosystems across Canada’s coasts, highlighting commonalities and differences in environmental conditions, plant, habitat, and community structure, as well as current trends and human impacts. Across regions, eelgrass life history, phenology, and general species assemblages are similar. However, distinct regional differences occur in environmental conditions, particularly with water temperature and nutrient availability. There is considerable variation in the types and strengths of human activities among regions. The impacts of coastal development are prevalent in all regions, while other impacts are of concern for specific regions, e.g., nutrient loading in the Atlantic and impacts from the logging industry in the Pacific. In addition, climate change represents a growing threat to eelgrass meadows. We review current management and conservation efforts and discuss the implications of observed differences from coast to coast to coast.
... Marine connectivity research has primarily focused on the connectivity of coral reefs or pelagic species, but the connectivity of other patchy nearshore habitat types and the species that disperse among them remains poorly understood (Bryan-Brown et al., 2017). Seagrass, like coral, provides foundational biogenic habitat for a high level of biodiversity (Orth et al., 1984), including communities of epifaunal invertebrates (Heck and Thoman, 1984;Duffy et al., 2015). The patchy distribution of seagrass meadows across the seascape may create the structure for a metacommunity of seagrass-associated species that are connected by animal movement (Bell, 2006;Boström et al., 2006;Whippo et al., 2018). ...
... Eelgrass occurs to a maximum depth of 10 m depending on turbidity (Christiaen et al., 2015) and can form meadows that range in size from a few seasonally intermittent shoots to more permanent meadows greater than 30 km 2 (Murphy G. E. P. et al., 2021). As a primary producer and coastal habitat forming species, eelgrass provides habitat and a productive algal food source for multiple trophic levels (Heck et al., 2008;Amundrud et al., 2015;Duffy et al., 2015;Huang et al., 2015). Eelgrass has also been identified as an ecological conservation priority for current marine conservation planning efforts in BC (Gale et al., 2019;Rubidge et al., 2020). ...
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The dispersal of marine organisms is a critical process for the maintenance of biodiversity and ecosystem functioning across a seascape. Understanding the patterns of habitat connectivity that arise from the movement of multiple species can highlight the role of regional processes in maintaining local community structure. However, quantifying the probability and scale of dispersal for marine organisms remains a challenge. Here, we use a biophysical model to simulate dispersal, and we conduct a network analysis to predict connectivity patterns across scales for the community of invertebrates associated with seagrass habitat in British Columbia, Canada. We found many possible connections and few isolated habitat meadows, but the probability of most connections was low. Most habitat connections occurred within 3 days of dispersal time over short distances, indicating potential limits to long distance dispersal and little effect of species-specific dispersal abilities on the potential spatial extent of habitat connectivity. We then highlight the different roles that individual seagrass meadows can play in maintaining network connectivity. We also identify clusters of connected meadows and use these clusters to estimate the spatial scale of community dynamics. The connectivity patterns generated by our dispersal simulations highlight the importance of considering marine communities in their broad seascape context, with applications for the prioritization and conservation of habitat that maintains connectivity.
... Sample collection. Samples were collected from 16 different globally distributed sites by researchers in the Zostera Experimental Network (ZEN) ( Table 1) (92). Samples were collected subtidally at ;1-m depth using a modified version of the collection protocol previously described by Fahimipour et al. (25). ...
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Seagrasses are marine flowering plants that provide critical ecosystem services in coastal environments worldwide. Marine fungi are often overlooked in microbiome and seagrass studies, despite terrestrial fungi having critical functional roles as decomposers, pathogens or endophytes in global ecosystems. Here we characterize the distribution of fungi associated with the seagrass, Zostera marina, using leaves, roots, and rhizosphere sediment from 16 locations across its full biogeographic range. Using high throughput sequencing of the ribosomal internal transcribed spacer (ITS) region and 18S ribosomal RNA gene, we first measured fungal community composition and diversity. We then tested hypotheses of neutral community assembly theory and the degree to which deviations suggested amplicon sequence variants (ASVs) were plant-selected or dispersal-limited. Finally, we identified a core mycobiome and investigated the global distribution of differentially abundant ASVs. We found that the fungal community is significantly different between sites and that the leaf mycobiome follows a weak, but significant pattern of distance decay in the Pacific Ocean. Generally, there was evidence for both deterministic and stochastic factors contributing to community assembly of the mycobiome, with most taxa assembling through stochastic processes. The Z. marina core leaf and root mycobiomes were dominated by unclassified Sordariomycetes spp., unclassified Chytridiomycota lineages (including Lobulomycetaceae spp.), unclassified Capnodiales spp. and Saccharomyces sp. It is clear from the many unclassified fungal ASVs and fungal functional guilds, that knowledge of marine fungi is still rudimentary. Further studies characterizing seagrass-associated fungi are needed to understand the roles of these microorganisms generally and when associated with seagrasses. Importance Fungi have important functional roles when associated with land plants, yet very little is known about the roles of fungi associated with marine plants, like seagrasses. In this study, we report the results of a global effort to characterize the fungi associated with the seagrass, Zostera marina, across its full biogeographic range. Although we defined a putative global core fungal community, it is apparent from the many fungal sequences and predicted functional guilds that had no matches to existing databases, that general knowledge of seagrass-associated fungi and marine fungi generally is lacking. This work serves as an important foundational step towards future work investigating the functional ramifications of fungi in the marine ecosystem.
... Data like these can provide context for experimental manipulations that investigate ecosystem function (Dossena et al., 2012), be linked with environmental or paleoecological data to examine ecological change over time (Kidwell, 2001(Kidwell, , 2007Olszewski and Kidwell, 2007;Tyler and Kowalewski, 2017;Hyman et al., 2019), or identify species that may be useful indicators of environmental change (Schröder et al., 2015). More detailed information about the relative strength of bottom-up and top-down control of epiphytes, macroalgae, and the herbivorous species that keep them in check is important for the conservation, management and restoration of seagrass ecosystems (Hays, 2005;Valentine, 2006, 2007;Poore et al., 2009;Hammerschlag-Peyer et al., 2013;Duffy et al., 2015;Lefcheck and Duffy, 2015). For example, marine resource managers might be interested in linking spatial differences in nutrient inputs to secondary production of invertebrate species or the morphology and shoot density of seagrasses, given the relevance of these variables to many economically valuable fish and crustaceans (Edgar and Shaw, 1995;Rakocinski et al., 2008). ...
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Seagrasses form vast meadows of structurally complex habitat that support faunal communities with greater numbers of species and individuals than nearby unstructured habitats. The Gulf coast of peninsular Florida represents a natural laboratory ideally suited to the study of processes that shape seagrass-associated invertebrate and fish communities within meadows of a single species of seagrass, Thalassia testudinum. This suitability arises from a pronounced structural and chemical gradient that exists over ecologically relevant spatial and temporal scales, as revealed by extensive monitoring of water quality and seagrass. We hypothesized that seagrass-associated invertebrate communities would vary across five estuarine systems spread along a spatial gradient in phosphorus concentration, an important driver of seagrass and phytoplankton growth in this region. The quantitative results based on data acquired at 25 stations (75 samples, 52,086 specimens, and 161 taxa) indicated that each of the five estuarine systems were distinct with regard to species composition and differences among systems were driven by abundant or relatively common species. In addition, we found evidence to indicate food webs in seagrass meadows along this gradient may differ, especially in the relative dominance of algal grazers and predatory invertebrates. These changes in species composition and trophic roles could be driven by phosphorus directly, through increases in rates of primary production with higher concentrations of phosphorus, or indirectly, through nutrient-mediated changes in the physical structure of the seagrass canopy. Our results suggest that differences in the habitat created by T. testudinum under differing phosphorus supplies lead to ecologically significant shifts in macroinvertebrate communities.
... Given the current global scenario of expansion of tropical macrophyte species (Anton et al., 2019;Beca-Carretero et al., 2020;Winter et al., 2020), the global and local regression of seagrass meadows in the Mediterranean Sea (Waycott et al., 2009;Boudouresque et al., 2021) and the accelerated tropicalisation of the Mediterranean Sea (Bianchi and Morri, 2003;Vergeś et al., 2014), understanding the community effects that tropical habitatforming species have on native seagrass habitats is key for adopting meaningful conservation and management practices. Studying associated epifaunal assemblages is particularly relevant because many of these organisms play a critical role in food webs dynamics and structure and can also be key grazers determining competitive outcomes amongst primary producers in seagrass beds (e.g., Taylor, 1998;Heck et al., 2000;Heck and Valentine, 2006;Duffy et al., 2015). ...
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The introduction and successful expansion of tropical species into temperate systems is being exacerbated by climate change, and it is particularly important to identify the impacts that those species may have, especially when habitat-forming species are involved. Seagrass meadows are key shallow coastal habitats that provide critical ecosystem services worldwide, and they are threatened by the arrival of non-native macroalgae. Here, we examined the effects of Halimeda incrassata, a tropical alga that has recently colonized the Mediterranean Sea, on epifaunal assemblages associated with Cymodocea nodosa seagrass meadows of Mallorca Island (Western Mediterranean Sea). This invasive macroalga is an ecological engineer and thus has a high potential of modifying native habitats. A seagrass meadow colonized by H. incrassata exhibited important changes on associated epifaunal assemblages, with an increase in abundance and diversity, particularly driven by higher abundances of Gammaridae, Polychaeta, Copepoda and Caprellidae. Given the key ecological contribution of epifauna to food webs, these alterations will likely have important implications for overall food web structure and ecosystem functioning of native ecosystems.
... Furthermore, seagrass protection efforts can prevent the degradation or loss of seagrass ecosystem services in the ecosystems of coastal waters, especially for protecting marine biodiversity. Moreover, the damage to seagrass can have negative implications by decreasing the productivity of marine resources, disrupting trophic interactions, and reducing stability in the natural ecosystems in the marine environment (Duffy 2006;Duffy et al. 2015;Best and Stachowicz 2012). In addition, the loss of seagrass vegetation can have a direct effect on fish that need seagrass as a habitat (Patro et al. 2017;Mishra et al. 2019). ...
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Seagrass-associated fish species’ richness: evidence to support conservation along the South Coast of Lombok Island, Indonesia. Biodiversitas 22: 988-998. The concept of seagrass conservation at a global scale tends to be less appropriate with regard to the environmental conditions at the regional and local scales, and thus, there is a need for scientific studies at the regional and local scales to support conservation measures. This research aimed to describe the importance of seagrass conservation based on the species richness of seagrass-associated fish. Data were collected from seven seagrass locations using surveys and observation. Data on the fish species present were collected with the gear used by small-scale fishermen to catch fish in the seagrass area and the surrounding waters. Data analysis was descriptive; the statistical analyses performed included calculation of the Shannon-Wiener index of diversity (H '), the Simpson evenness index (E), and the Morisita species richness index (D) as well as cluster analysis. All statistical analyses were performed in IBM SPSS Statistics 25. We found 104 fish species belonging to 38 families. Leiognathidae, Apogonidae, Clupeidae, Carangidae, Channidae, Sillaginidae, and Mullidae are families with high abundance, and 16 fish species have an abundance of individuals above the average value (192 individuals) of the total number of individuals (20,352). Meanwhile, 94.37% of the fish families are the target catch of small-scale fishermen (commercial fish). The diversity of fish species associated with seagrass in the study location is evidence of the survival of seagrass provision services at the local scale for fish. Therefore, scientific evidence of the species richness of fish, species yang domina, and its importance for small-scale fisheries at each seagrass bed in the study location can be used as a source of information for increasing and improving seagrass conservation efforts at the local scale.
... Seagrass meadows are increasingly recognized as high-value ecosystems due to the extraordinary biodiversity they sustain (Duffy et al., 2015;Nordlund et al., 2016;van Katwijk et al., 2016). In recent years, seagrass ecosystems have been significantly affected by natural and anthropogenic stresses (Schiel and Lilley, 2011;Polidoro et al., 2012), and experienced significant degradation (Bertness et al., 2014;Marin-Guirao et al., 2019). ...
Article
Algae-dominance in seagrass beds has been well recognized, however, the competitive relationship between seagrass and macroalgae along land-sea gradients and their ecological effects has received little attention. In this study, a field survey was conducted at the Yellow River Estuary to investigate the effects of macroalgal proliferation on seagrass and macrobenthic invertebrate communities. Our results suggested that strong competitive interaction existed between the two primary producers, and the positive or negative effects of macroalgae on seagrass growth varied along land-sea gradient. Furthermore, the dominant controlling factors on the biomass, density and diversity of macrobenthic invertebrate communities were found to vary accordingly, i.e., from features of the primary producers in the nearshore where macroalgae suppressed seagrass growth to hydrodynamic disturbance in the offshore where macroalgae facilitated seagrass growth. Our study emphasizes the importance to integrate interspecific competition into ecosystem-based management of seagrass ecosystem, and provides references for additional ecological indicators.
... We decided to test sediment nutrient enrichment rather than water column nu trient enrichment because a previous study nearby did not find any effect of water column nutrient enrichment on epiphyte load or on the associated epifauna after a 4 wk enrichment (cf. Duffy et al. 2015). Moreover, large blue mussels are found at the sediment interface, and filter-feeding organisms such as these are known to promote bio deposition and nutrients within sediments (Reusch et al. 1994). ...
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Multiple forms of environmental change and anthropogenic pressure co-occur in coastal marine ecosystems. These external forces affect ecosystem structure, functioning, and, eventually, services to humans. Studies that include more than 2 simultaneous stressors are still needed to understand potential interactions among multiple stressors. We evaluated single and interactive effects of density reduction of Zostera marina L. (a habitat-forming species), shading, and sediment nutrient enrichment on the response of Z. marina and its associated epifauna over 10 wk. Shading had the greatest effect on reducing the eelgrass relative leaf elongation rate (RLE), non-structural carbohydrate reserves, and eelgrass shoot density. A reduced eelgrass density sustained higher epifaunal densities and increased the eelgrass RLE. Sediment nutrient enrichment increased eelgrass shoot density but decreased epifaunal richness, diversity, and total abundance. Our disturbance and pair of stressors differed in their influence on diversity measures, but all affected assemblage structure. Most of the changes to the epifaunal assemblage and diversity likely occurred due to altered habitat availability and epiphytic algae load. We observed additive, antagonistic, and negatively synergistic interactions among our treatments, while most of the cumulative effects showed dominance by one stressor over another. Our results highlight the importance of field experiments that are based on multiple disturbances and stressors to determine their interaction type on communities.
... Seagrasses are foundation species that support high productivity and faunal diversity (Orth et al. 1984, Duffy et al. 2015. They form meadows separated by deeper water, un-vegetated seafloor, or other vegetated habitats, and associated fauna disperse among meadows (Boström et al. 2006(Boström et al. , 2010. ...
Article
Ecological communities are jointly structured by dispersal, density-independent responses to environmental conditions, and density-dependent biotic interactions. Metacommu- nity ecology provides a framework for understanding how these processes combine to determine community seagrass meadows along the British Columbia coast. We tested the hypothesis that eelgrass Zostera marina L. epifaunal invertebrate assemblages are influenced by local environ- mental conditions but that high dispersal rates at larger spatial scales dampen the effects of envi- ronmental differences. We used hierarchical joint species distribution modelling to understand the contribution of environmental conditions, spatial distance between meadows, and species co- occurrences to epifaunal invertebrate abundance and distribution across the region. We found that patterns of taxonomic compositional similarity among meadows were inconsistent with dis- persal limitation, and meadows in the same region were often no more similar to each other than meadows over 1000 km away. Abiotic environmental conditions (temperature, dissolved oxygen) explained a small fraction of variation in taxonomic abundance patterns across the region. We found novel co-occurrence patterns among taxa that could not be explained by shared responses to environmental gradients, suggesting the possibility that interspecific interactions influence sea- grass invertebrate abundance and distribution. Our results suggest that biodiversity and ecosys- tem functions provided by seagrass meadows reflect ecological processes occurring both within meadows and across seascapes and that management of eelgrass habitat for biodiversity may be most effective when both local and regional processes are considered.
... Historically, outbreaks of the pathogenic protist Labyrinthula zosterae ("wasting disease") has caused catastrophic die-off of eelgrass (Muehlstein et al., 1991), although its importance as a pathogen under current conditions in Europe seems limited (Brakel et al., 2014). Instead, factors such as water clarity, eutrophication, grazing pressure, and interspecific competition have been identified as culprits for eelgrass growth (Baden et al., 2010;Duffy et al., 2015). Especially important is the competition between eelgrass and algae that grow within meadows, often as epiphytes on the eelgrass itself. ...
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Eelgrass (Zostera marina) is a marine foundation species essential for coastal ecosystem services around the northern hemisphere. Like all macroscopic organisms, it possesses a microbiome which may play critical roles in modulating the interaction of eelgrass with its environment. For example, its leaf surface microbiome could inhibit or attract eukaryotic epibionts which may overgrow the eelgrass leading to reduced primary productivity and subsequent eelgrass meadow decline. We used amplicon sequencing of the 16S and 18S rRNA genes of prokaryotes and eukaryotes to assess the leaf surface microbiome (prokaryotes) as well as eukaryotic epibionts in-and outside lagoons on the German Baltic Sea coast. Bacterial microbiomes varied substantially both between sites inside lagoons and between open coastal and lagoon sites. Water depth, leaf area and biofilm chlorophyll a concentration explained a large amount of variation in both bacterial and eukaryotic community composition. Communities of bacterial and eukaryotic epibionts were highly correlated, and network analysis revealed disproportionate co-occurrence between a limited number of eukaryotic taxa and several bacterial taxa. This suggests that eelgrass leaf surface biofilms are a mosaic of the microbiomes of several eukaryotes, in addition to that of the eelgrass itself, and underlines that eukaryotic microbial diversity should be taken into account in order to explain microbiome assembly and dynamics in aquatic environments.
... billion. Although these values are estimates extrapolated from small-scale data 322 uninformed by the well-described variation in these services through time and space (Ralph et al., 323 2013;Duffy et al., 2015), and therefore must be interpreted with caution, they represent the best 324 available data for assessing the outcome of eelgrass decline for the ecological and economic well-325 being of the Chesapeake Bay. 326 ...
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Interactions among global change stressors and their effects at large scales are often proposed, but seldom evaluated. This situation is primarily due to lack of comprehensive, sufficiently long-term, and spatially-extensive datasets. Seagrasses, which provide nursery habitat, improve water quality, and constitute a globally-important carbon sink, are among the most vulnerable habitats on the planet. Here, we unite 31-years of high-resolution aerial monitoring and water quality data to elucidate the patterns and drivers of eelgrass ( Zostera marina ) abundance in Chesapeake Bay, USA, one of the largest and most valuable estuaries in the world with an unparalleled history of regulatory efforts. We show that eelgrass area has declined 29% in total since 1991, with wide-ranging and severe ecological and economic consequences. We go on to identify an interaction between decreasing water clarity and warming temperatures as the primary driver of this trend. Declining clarity has gradually reduced eelgrass over the past two decades, primarily in deeper beds where light is already limiting. In shallow beds, however, reduced visibility exacerbates the physiological stress of acute warming, leading to recent instances of decline approaching 80%. While degraded water quality has long been known to influence underwater grasses worldwide, we demonstrate a clear and rapidly emerging interaction with climate change. We highlight the urgent need to integrate a broader perspective into local water quality management, in the Chesapeake Bay and in the many other coastal systems facing similar stressors.
... Marine mesograzers are analogous to terrestrial herbivorous insects in their small size, their intimate interactions with their host plants (for food and shelter), and their critical roles in their community as both prey and pro cient consumers (Hay et al. 1987;Duffy et al. 2001;Jaschinski and Sommer 2008;Duffy et al. 2015). Terrestrial insects readily evolve population-level differences in host use traits (Thompson 2005), suggesting that marine mesograzers should similarly local adapt. ...
... SEMs have been used to evaluate hypothesised networks of causal relationships in ecological systems (e.g. Byrnes et al. 2011;Duffy et al. 2015;Jing et al. 2015), but have rarely been applied to Arctic ecology (but see Juhasz et al. 2020). Specifically, the objective of this research was to determine the direct and indirect effects of climatic and local biotic and abiotic drivers on musk ox and lemming abundance in Zackenberg. ...
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Arctic ecosystems are particularly vulnerable to impacts of climate change; however, the complex relationships between climate and ecosystems make incorporating effects of climate change into population management difficult. This study used structural equation modelling (SEM) and a 24-year multifaceted monitoring data series collected at Zackenberg, North-East Greenland, to untangle the network of climatic and local abiotic and biotic drivers, determining their direct and indirect effects on two herbivores: musk ox ( Ovibos moschatus ) and collared lemming ( Dicrostonyx groenlandicus ). Snow conditions were determined to be the central driver within the system, mediating the effects of climate on herbivore abundance. Under current climate change projections, snow is expected to decrease in the region. Snow had an indirect negative effect on musk ox, as decreased snow depth led to an earlier start to the Arctic willow growing season, shown to increase fecundity and decrease mortality. Musk ox are therefore expected to be more successful under future conditions, within a certain threshold. Snow had both positive and negative effects on lemming, with lemming expected to ultimately be less successful under climate change, as reduction in snow increases their vulnerability to predation. Through their capacity to determine effects of climatic and local drivers within a hierarchy, and the relative strength and direction of these effects, SEMs were demonstrated to have the potential to be valuable in guiding population management.
... The feeding activities of herbivore fishes increase seagrass productivity by removing older seagrass blades and cleaning epiphytes, sometimes increasing light availability (Douglas et al 2018). In general, the gastropods:crustacean ratio in the mesograzer community varies from region to region (Duffy et al 2015). Seagrass beds provide a complex physical structure with various associated biota as primary products, including phytoplankton, periphyton, and macroalgae. ...
Article
The seagrass ecosystem plays an essential role in the ecological system in coastal areas. The seagrass ecosystem has no natural attractiveness compared to coral reef ecosystems and mangroves. The seagrass ecosystem receives less attention and appreciation due to the lack of public knowledge about seagrass in general and the benefits it provides. Lack of public awareness has led to a decline in perceptions of the seagrass ecosystem services' importance. The Teluk Bakau area on Bintan Island also faces the same problem with the seagrass ecosystem existence has not been utilized optimally because the community is not interested in empowering the seagrass ecosystem, especially for ecotourism activities. Therefore, to increase public interest in seagrass ecosystem services, it is necessary to study the understanding and improvement of communication of seagrass ecosystem services to the community from a socio-ecological perspective. This study uses flag modeling analysis divided into three criteria: ecological, socioeconomic , and institutional. The ecological criteria found four species of seagrasses and 22 species of marine biota, and 12 marine biota species with economic value. Another result found two sub-criteria from critical threshold value (CTV) analysis were not appreciated categories, particularly seagrass cover and the presence of crustaceans. In the socioeconomic criteria, there is one sub-criterion with not appreciated categories, specifically the income provision. Moreover, on the institutional criteria, the sub-criterion with not appreciative categories was the manager's activeness. Based on the flag modeling analysis results, the socio-ecological perspective in Teluk Bakau is quite appreciative.
... Monitoring included two methods: 1) suction sampling, a method that could be used consistently across all treatments and 2) shoot collection, a common method used for sampling invertebrates on eelgrass [37,38], which permitted the assessment of invertebrate assemblages with and without oyster reefs present and comparisons with natural eelgrass beds. ...
Article
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Restoration projects provide a valuable opportunity to experimentally establish foundational habitats in different combinations to test relative effects on community assembly. We evaluated the development of macroinvertebrate communities in response to planting of eelgrass (Zostera marina) and construction of reefs intended to support the Olympia oyster (Ostrea lurida) in the San Francisco Estuary. Plots of each type, alone or interspersed, were established in 2012 in a pilot living shorelines project, and quarterly invertebrate monitoring was conducted for one year prior to restoration, and three years post-restoration using suction sampling and eelgrass shoot collection. Suction sampling revealed that within one year, oyster reefs supported unique invertebrate assemblages as compared to pre-restoration conditions and controls (unmanipulated mudflat). The eelgrass invertebrate assemblage also shifted, becoming intermediate between reefs and controls. Interspersing both types of habitat structure led eelgrass invertebrate communities to more closely resemble those of oyster reefs alone, though the eelgrass assemblage maintained some distinction (primarily by supporting gammarid and caprellid amphipods). Eelgrass shoot collection documented some additional taxa known to benefit eelgrass growth through consumption of epiphytic algae; however, even after three years, restored eelgrass did not establish an assemblage equivalent to natural beds, as the eelgrass sea hare (Phyllaplysia taylori) and eelgrass isopod (Pentidotea resecata) remained absent or very rare. We conclude that the restoration of two structurally complex habitat types within tens of meters maximized the variety of invertebrate assemblages supported, but that close interspersion dampened the separately contributed distinctiveness. In addition, management intervention may be needed to overcome the recruitment limitation of species with important roles in maintaining eelgrass habitat.
... Perform modularised studies: These offer a different path for scientists to engage in multi-perspective research. The replication of observations and experiments in different locations offers an unprecedented statistical power to overcome context-specific results Duffy et al., 2015;Kemppinen et al., 2021). Additionally, already the discussion towards such an endeavour contributes to avoiding lock-in debates as it requires to integrate different views on which question to pose and prioritise and how to analyse the results. ...
Article
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While environmental science, and ecology in particular, is working to provide better understanding to base sustainable decisions on, the way scientific understanding is developed can at times be detrimental to this cause. Locked‐in debates are often unnecessarily polarised and can compromise any common goals of the opposing camps. The present paper is inspired by a resolved debate from an unrelated field of psychology where Nobel laureate David Kahneman and Garry Klein turned what seemed to be a locked‐in debate into a constructive process for their fields. The present paper is also motivated by previous discourses regarding the role of thresholds in natural systems for management and governance, but its scope of analysis targets the scientific process within complex social‐ecological systems in general. We identified four features of environmental science that appear to predispose for locked‐in debates: (1) The strongly context‐dependent behaviour of ecological systems. (2) The dominant role of single hypothesis testing. (3) The high prominence given to theory demonstration compared investigation. (4) The effect of urgent demands to inform and steer policy. This fertile ground is further cultivated by human psychological aspects as well as the structure of funding and publication systems. The ecological discipline is prone to locked in debates that hamper theory development and reduce it efficiency in influencing policy development. We outline the mechanisms behind these locked in debates and discuss possible ways to prevent these.
... To accurately generalize the effects of salinization on lake food webs, we need to compare responses using standardized methods while incorporating local differences in species composition and environmental conditions of lake water. Because experimental networks that replicate and standardize experiments across space and time can overcome this limitation [e.g., Nutrient Network (36), Zostera Experimental Network (37), and the Swedish Infrastructure for Ecosystem Science (SITES) AquaNet (38)], we established an experimental network of 16 sites across North America and Europe to identify responses of lake food webs to salinization triggered by NaCl, one of the most common salt types leading to the salinization of freshwater lakes (e.g., from road salt use). Further, using zooplankton communities from natural habitats has an advantage over short-duration (e.g., 48-h toxicity tests), single-species laboratory studies because such an approach encompasses a greater diversity of species and naturally occurring predator-prey and competitive interactions within the zooplankton community. ...
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Human-induced salinization caused by the use of road deicing salts, agricultural practices, mining operations, and climate change is a major threat to the biodiversity and functioning of freshwater ecosystems. Yet, it is unclear if freshwater ecosystems are protected from salinization by current water quality guidelines. Leveraging an experimental network of land-based and in-lake mesocosms across North America and Europe, we tested how salinization—indicated as elevated chloride (Cl ⁻ ) concentration—will affect lake food webs and if two of the lowest Cl ⁻ thresholds found globally are sufficient to protect these food webs. Our results indicated that salinization will cause substantial zooplankton mortality at the lowest Cl ⁻ thresholds established in Canada (120 mg Cl ⁻ /L) and the United States (230 mg Cl ⁻ /L) and throughout Europe where Cl ⁻ thresholds are generally higher. For instance, at 73% of our study sites, Cl ⁻ concentrations that caused a ≥50% reduction in cladoceran abundance were at or below Cl ⁻ thresholds in Canada, in the United States, and throughout Europe. Similar trends occurred for copepod and rotifer zooplankton. The loss of zooplankton triggered a cascading effect causing an increase in phytoplankton biomass at 47% of study sites. Such changes in lake food webs could alter nutrient cycling and water clarity and trigger declines in fish production. Current Cl ⁻ thresholds across North America and Europe clearly do not adequately protect lake food webs. Water quality guidelines should be developed where they do not exist, and there is an urgent need to reassess existing guidelines to protect lake ecosystems from human-induced salinization.
... Perform modularised studies: These offer a different path for scientists to engage in multi-perspective research. The replication of observations and experiments in different locations offers an unprecedented statistical power to overcome context-specific results Duffy et al., 2015;Kemppinen et al., 2021). Additionally, already the discussion towards such an endeavour contributes to avoiding lock-in debates as it requires to integrate different views on which question to pose and prioritise and how to analyse the results. ...
Article
While environmental science, and ecology in particular, is working to provide better understanding to base sustainable decisions on, the way scientific understanding is developed can at times be detrimental to this cause. Locked-in debates are often unnecessarily polarized and can compromise any common goals of the opposing camps. The present paper is inspired by a resolved debate from an unrelated field of psychology where Nobel laureate David Kahneman and Garry Klein turned what seemed to be a locked-in debate into a constructive process for their fields. The present paper is also motivated by previous discourses regarding the role of thresholds in natural systems for management and governance, but its scope of analysis targets the scientific process within complex social-ecological systems in general. We identified five features of environmental science that appear to predispose for locked-in debates: 1) The strongly context dependent behaviour of ecological systems. 2) The dominant role of single hypothesis testing. 3) The high prominence given to theory demonstration compared investigation. 4) The effect of urgent demands to inform and steer policy. This fertile ground is further cultivated by human psychological aspects as well as the structure of funding and publication systems.
... One of the main causes of seagrass decline is the disruption of natural feedbacks that promote seagrass growth and sustenance (Duarte, 2002;Orth et al., 2006). Stabilizing feedbacks (i.e., negative feedback loops) control seagrass ecosystems at multiple scales O'Brien et al., 2017), from supporting mesograzer populations at the meter scale (Valentine and Duffy, 2006;Duffy et al., 2015) to genetic diversity at the ecosystem scale (Procaccini et al., 2007;Reynolds et al., 2013). For example, grazing by sea urchins results in the reduction of aboveground seagrass biomass, which increases the predation pressure on sea urchins. ...
... To examine these effects and their generality, we used geographically distributed experiments, which have been heralded for their ability to test for consistency in mechanistic processes and associated biodiversity patterns across habitats, ecosystems and biogeographical regions 41,42 . This approach has so far focused on individual processes in specific habitats, such as biodiversityproductivity relationships in grasslands 43 , nutrient impacts on seagrasses 44 or warming effects in tundra 45 . Here, we adapted this approach to test for, and rank in importance, three ecological processes that could simultaneously affect how facilitation cascades control biodiversity across habitats, ecosystems and regions 46 . ...
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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.
... Our understanding of how environmental conditions alter the outcomes of species interactions would benefit from manipulative experiments replicated in space and time (Menge and Sutherland 1987, Borer et al. 2014a, Duffy et al. 2015. Two recent studies used this rigorous approach to compare the impact of resources and herbivory on vegetation. ...
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Abstract Burrowing animals profoundly influence plant communities, and changes in the burrower and plant communities together with changing abiotic parameters can shift the influence of burrowers on plants. However, we lack an ability to predict when, where, and how burrowers will influence vegetation. To begin to understand how naturally, varying environmental conditions influence the impacts of burrowers, we need to examine how burrower impacts on marsh plants differ across sites differing in environmental conditions. We manipulated crab presence for multiple years and measured the responses of the dominant plants, Pacific cordgrass (Spartina foliosa) and perennial pickleweed (Sarcocornia pacifica), at three sites in northern California and two sites in southern California. Southern California (Point Conception, CA, to the U.S.–Mexico border) experiences higher air and water temperatures, lower precipitation, and higher porewater salinity levels. Combining data from these field studies with laboratory studies allowed us to generate predictions about burrowing crab effects in salt marshes. Our models included (1) an estimate of grazing pressure on marsh plants by the dominant burrowing crab (Pachygrapsus crassipes) and (2) several soil biogeochemical measurements. Crab effects varied from strongly positive to strongly negative and depended upon estimated crab grazing pressure and edaphic conditions (salinity, ammonium, and nitrate). Relative to crabs at other sites, crabs enhanced cordgrass at sites with intermediate levels of ammonium and extreme salinities. The dependence of crab effects on edaphic conditions suggests that projected interannual variability in temperature, precipitation, and nutrients could lead to more temporally variable impacts of crabs on cordgrass. Understanding the environmental controls on these interactions will help promote cordgrass productivity and stabilize salt marsh ecosystems.
... Seagrass has a wide geographic distribution and presence, except in Antarctica, in many shallow coastal and oceanic waters around the world [12]; therefore, related population and community processes can be compared on a wide spatial scale [13]. ey support abundant and generally well-known macrofauna, the density and diversity of which also surpass the existing in nearby bare sediment fields [14,15]. ...
Article
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Large-scale research on seagrass-associated benthic fauna is very important for future regional marine conservation. In our study, we investigated spatial and latitudinal variation of benthic macroinvertebrate assemblages associated to Zostera noltei Hornemann, 1832 beds from five semi-enclosed coastal systems (SECSs) ranging from 23°N to 34°N along the Atlantic coast of Morocco. Overall, 17,320 individuals were reported as belonging to 96 taxa. The ecological community descriptors differ significantly at the level of the site. Specific richness showed an inconsistent significant pattern with latitude. The multivariate analyses of the assemblage’s composition showed 57% of total variation observed in benthic assemblages, while the PERMANOVA analysis confirmed that this variation is significant at the level of the site. According to DistLM results, variations in belowground biomass, and percentage of mud, were the important predictor variables explaining this variation along the large scale of the studied SECS. However, such patterns could be related to other factors such as habitat heterogeneity and regional, biogeographic, and anthropogenic factors. The present study marked the first attempt on broad-scale ecological research of seagrass beds in Morocco and offers baseline data for planning the broad-scale conservation of biodiversity in seagrass beds that remain suffering from multiple human-induced threats such as coastal developments and climate change.
... First, SEM can be used to test hypotheses about network structure, decomposing total effects into direct and indirect and dealing with reciprocal effects, multiple observable and unobservable variables (see Glossary), multiple outcomes, and the relationships within and between them (Hoyle, 2012;Barringer et al., 2013). Such networks are useful in quantifying cascading effects and in exploring potential interdependency within and between intrinsic and extrinsic factors (e.g., Chen et al., 2013;Duffy et al., 2015). Second, in SEM, relationships between variables are interpreted as causative rather than associative (Box 1). ...
Article
Structural equation modeling (SEM) can illuminate complex interaction networks of the sort found in ecology. However, selecting optimally complex, data‐supported SEM models and quantifying their uncertainty are difficult processes. To this end, we recommend a formal model selection approach (MSA) that uses information criteria. Using a suite of numerical simulations, we compare MSA‐SEM against two traditional methods. We find that MSA‐SEM exhibits superior, unbiased results under the suboptimal realistic conditions characteristic of ecological studies. We then provide a road map for MSA‐SEM and demonstrate its use via a case study. We illustrate the unique abilities of SEM to confirm a network structure within the realm of known causal pathways and delineate the boundaries within which MSA‐SEM should be applied.
... Zostera marina (eelgrass) is a widespread seagrass species that generates ecological diversity and economically important ecosystems along coast lines throughout much of the northern hemisphere (Marba et al., 2006;Duffy et al., 2015). Seagrass habitats are considered one of the most valuable marine ecosystems on earth (Costanza et al., 1997;Hemminga and Duarte, 2000) because they support marine life, including epiphytic organisms as well as coastal fisheries resources (Coles et al., 1993;Hemminga and Duarte, 2000), and contribute to marine environments by stabilizing bottom sediment and maintaining coastal water quality (Komatsu and Yamano, 2000). ...
Article
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Zostera marina (eelgrass) is a widespread seagrass species that forms diverse and productive habitats along coast lines throughout much of the northern hemisphere. The present study investigated the microbial consortia of Z. marina growing at Futtsu clam-digging beach, Chiba prefecture, Japan. The following environmental samples were collected: sediment, seawater, plant leaves, and the root-rhizome. Sediment and seawater samples were obtained from three sampling points: inside, outside, and at the marginal point of the eelgrass bed. The microbial composition of each sample was analyzed using 16S ribosomal gene amplicon sequencing. Microbial communities on the dead (withered) leaf surface markedly differed from those in sediment, but were similar to those in seawater. Eelgrass leaves and surrounding seawater were dominated by the bacterial taxa Rhodobacterales (Alphaproteobacteria), whereas Rhodobacterales were a minor group in eelgrass sediment. Additionally, we speculated that the order Sphingomonadales (Alphaproteobacteria) acts as a major degrader during the decomposition process and constantly degrades eelgrass leaves, which then spread into the surrounding seawater. Withered eelgrass leaves did not accumulate on the surface sediment because they were transported out of the eelgrass bed by wind and residual currents unique to the central part of Tokyo Bay.
... The consumption of seagrass epiphytes by invertebrate epifauna is, on average, stronger than the bottom-up forces of nutrients, leading to positive indirect effects of herbivores to seagrass (Hughes et al. 2004, Valentine & Duffy 2006, Heck & Valentine 2007. In communities of the seagrass Zostera marina, the presence of top-down forcing from invertebrate epifauna appears relatively consistent around the world but can vary in strength and with epifauna community composition, suggesting at least some commonality in structuring forces regardless of geography (Duffy et al. 2015). Such strong interactions are not limited to lower trophic levels. ...
Article
Previous research in southeast Alaska on the effects of sea otters Enhydra lutris in seagrass Zostera marina communities identified many but not all of the trophic relationships that were predicted by a sea otter-mediated trophic cascade. To further resolve these trophic connections, we compared biomass, carbon (δ ¹³ C) and nitrogen (δ ¹⁵ N) stable isotope (SI), and fatty acid (FA) data from 16 taxa at 3 sites with high and 3 sites with low sea otter density (8.2 and 0.1 sea otters km ⁻² , respectively). We found lower crab and clam biomass in the high sea otter region but did not detect a difference in biomass of other seagrass community taxa or the overall community isotopic niche space between sea otter regions. Only staghorn sculpin differed in δ ¹³ C between regions, and Fucus , sugar kelp, butter clams, dock shrimp, and shiner perch differed in δ ¹⁵ N. FA analysis indicated multivariate dissimilarity in 11 of the 15 conspecifics between sea otter regions. FA analysis found essential FAs, which consumers must obtain from their diet, including 20:5ω3 (EPA) and 22:6ω3 (DHA), were common in discriminating conspecifics between sea otter regions, suggesting differences in consumer diets. Further FA analysis indicated that many consumers rely on diverse diets, regardless of sea otter region, potentially buffering these consumers from sea otter-mediated changes to diet availability. While sea otters are major consumers in this system, further studies are needed to understand the mechanisms responsible for the differences in biomarkers between regions with and without sea otters.
... Mosquitofish could be used in global comparative experiments (e.g. Duffy et al., 2015) to test the fundamental tenets of freshwater ecology, while incorporating an unprecedented scope of natural ecological variation. The recent publication of a high-quality genome for one mosquitofish species (Gambusia affinis) increases their potential use as a genetic model in laboratory and field studies (Hoffberg et al., 2018 WM;Shao et al., 2020 WM). ...
Article
The most widespread and numerous inland fish in the world is likely the mosquitofish (Gambusia affinis and G. holbrooki, Poeciliidae). Much has been written about the basic biology, the current distribution and the negative impacts of non‐native populations of mosquitofish. Here, we instead review the relationship of humanity with mosquitofish. First, we review the early literature on the species and aim to resolve its path towards becoming the globally dominant fish for biological control of mosquitoes. We identify the initial advocates of mosquitofish use, we examine the reasons behind their advocacy, and we document the spread of their viewpoints into and from the globally foundational mosquito control texts. Second, we identify the people and institutions that facilitated early international translocations of mosquitofish, including, among others, David Starr Jordan, the Rockefeller Foundation and the International Red Cross. Third, we discuss the reduction in mosquitofish translocation and use during and after WWII, initially stemming from the discovery and use of other methods, like DDT and later from a recognition of the negative ecological consequences of non‐native mosquitofish populations. Fourth, we propose that the future utility of mosquitofish is largely in its value as a model study organism. We provide an overview of the contributions mosquitofish have made to some major fields in biology. Finally, we suggest that the value of mosquitofish as a model system should increase into the future, behind a momentum of research advances, and as human‐mediated range expansion will permit access to mosquitofish by yet greater numbers of biologists worldwide.
... The factors affecting grazer-epiphyte interactions in seagrass ecosystems are complex (Jernakoff et al. 1996), and the inclusion and exclusion of predators have immediate effects on grazers and epiphyte abundance (Reynolds et al. 2014(Reynolds et al. , Östman et al. 2016. Reduced grazing by predators increased epiphyte abundance, and this effect was greater than that of fertilization (Duffy et al. 2015(Duffy et al. , Östman et al. 2016. Hence, grazing by epifauna is a dominant factor limiting the growth of epiphytic diatoms on host macrophytes. ...
Article
We present a descriptive account of the dynamics of epiphytic diatoms, epifauna, and the leaf surface area of Zostera marina in a shallow water ecosystem. We hypothesized that the growth stage of the host macrophyte (i.e., leaf surface area) influenced the presence of epiflora and epifauna, as well as that the leaf surface area and epifaunal population density affected the cell density and species composition of epiphytic diatoms. To evaluate this hypothesis, we quantified the leaf surface area of a host macrophyte (Zostera marina), the presence of epifauna, and the community of epiphytic diatoms that could be observed on the leaves of Z. marina during the period from May 2017 to December 2018. We conducted a descriptive analysis of the time-series observations of leaf surface area, epiphytic diatom density, and epifauna population density. Epiphytic diatom density was low and epifauna density was high during the growing season of Z. marina. Epiphytic diatom density was high and epifauna density was low during the maturation and senescence periods of Z. marina. Our analysis shows that epifauna densities lagged epiflora densities by at least four months, and that epiflora densities lagged leaf area by four months. Therefore, we hypothesized that herbivorous gastropods and amphipods could alter species composition via their preference of food items (active choice) or by ingesting more of the species that were structurally more available (passive preference).
... One of the main causes of seagrass decline is the disruption of natural feedbacks that promote seagrass growth and sustenance (Duarte, 2002;Orth et al., 2006). Stabilizing feedbacks (i.e., negative feedback loops) control seagrass ecosystems at multiple scales O'Brien et al., 2017), from supporting mesograzer populations at the meter scale (Valentine and Duffy, 2006;Duffy et al., 2015) to genetic diversity at the ecosystem scale (Procaccini et al., 2007;Reynolds et al., 2013). For example, grazing by sea urchins results in the reduction of aboveground seagrass biomass, which increases the predation pressure on sea urchins. ...
Article
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Seagrasses are threatened worldwide due to anthropogenic and natural disturbances disrupting the multiple feedbacks needed to maintain these ecosystems. If the disturbance is severe enough, seagrass systems may undergo a regime shift to a degraded system state that is resistant to recovery. In Florida Bay, Florida, United States, two recent, large-scale disturbances (a drought-induced seagrass die-off in 2015 and Hurricane Irma in 2017) have caused 8,777 ha of seagrass beds to degrade into a turbid, unvegetated state, causing a large sediment plume. Using satellite imagery digitization and long-term seagrass cover data, we investigate the expansion of this sediment plume between 2008 and 2020 and the potential interaction of this sediment plume with seagrass recovery in two focal basins in Florida Bay affected by the die-off, Johnson and Rankin. The average size of the sediment plume increased by 37% due to the die-off and Hurricane Irma, increasing from an average of 163.5 km ² before the disturbances to an average of 223.5 km ² . The expansion of the plume was basin-specific, expanding into Johnson after the 2015 seagrass die-off with expansive and long-lasting effects, but only expanding into Rankin after Hurricane Irma with less severe and short-term effects. Furthermore, the sediment plume was negatively correlated with seagrass cover in Johnson, but held no relationship with seagrass cover in Rankin. Thus, different disturbances can act upon seagrass ecosystems at varying scales with varying consequences. This study illustrates the advantage of combining satellite imagery with field data to monitor disturbances as well as highlights the importance of investigating disturbances of seagrass ecosystems at various scales to comprehend seagrass resilience in the context of future extreme events.
... This indicates that in the balance between bottom-up and topdown effects the top-down effect is more pronounced, and small epifauna is over-predated by high abundances of intermediate invertebrates and fish. This is in accordance with manipulative field experiments where nutrient addition and grazer exclusion affected the epifauna composition and abundance (Mosknes al. 2008;Duffy et al., 2015). The later study used 15 seagrass beds from the whole Zostera marina distribution area as a model study. ...
Article
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The interaction between bottom-up and top-down processes in coastal ecosystems has Marinebeen scarcely studied so far. Temporal changes in trophic interactions of Zostera marina along the Swedish west coast are relatively well studied, with the exception of epifaunal communities. Epifauna was used as a model study to explore resource (bottom-up) or predator (top-down) regulated in a vegetated ecosystem. We conducted a 21-year comparative study (1997 and 2018) using epifauna of 19 Zostera marina meadows along the Swedish Skagerrak coast. Large changes were observed in the composition of small (0.2–1 mm) and large (> 1 mm) epifauna. In the small-sized epifauna, the nematode Southernia zosterae and harpacticoids showed an increase of 90% and a decrease of 50% of their abundances, respectively. In the large-sized epifauna, the polychaete Platynereis dumerilii and chironomid larvae were absent in 1997 but thrived in 2018 (> 2000 ind. m−2). Mesoherbivores (Idoteids and gammarids) were locally very abundant in 1997 but disappeared in 2018. An 83% decline of mytilids settling in Zostera marina leaves was observed. Our results showed that epifauna is predominantly top-down regulated. An integrative framework of the study area is outlined to shed light on the causes and consequences of the environmental shifts reported in Zostera meadows from the northern Skagerrak area throughout the last three decades.
Article
Increasing human impact on the environment is causing drastic changes in disturbance regimes and how they prevail over time. Of increasing relevance is to further our understanding on biological responses to pulse disturbances (short duration) and how they interact with other ongoing press disturbances (constantly present). Because the temporal and spatial contexts of single experiments often limit our ability to generalize results across space and time, we conducted a modularized mesocosm experiment replicated in space (5 lakes along a latitudinal gradient in Scandinavia) and time (2 seasons, spring and summer) to generate general predictions on how the functioning and composition of multi‐trophic plankton communities (zoo‐, phyto‐ and bacterio‐plankton) respond to pulse disturbances acting either in isolation or combined with press disturbances. As pulse disturbance, we used short‐term changes in fish presence and as press disturbance, we addressed the ongoing reduction in light availability caused by increased cloudiness and lake browning in many boreal and subarctic lakes. First, our results show that the top‐down, pulse disturbance had the strongest effects on both functioning and composition of the three trophic levels across sites and seasons, with signs for interactive impacts with the bottom‐up, press disturbance on phytoplankton communities. Second, community composition responses to disturbances were highly divergent between lakes and seasons: temporal accumulated community turnover of the same trophic level either increased (destabilization) or decreased (stabilization) in response to the disturbances compared to control conditions. Third, we found functional recovery from the pulse disturbances to be frequent at the end of most experiments. In a broader context, these results demonstrate that top down, pulse disturbances, either alone or with additional constant stress upon primary producers caused by bottom‐up disturbances, can induce profound but often functionally reversible changes across multiple trophic levels, which are strongly linked to spatial and temporal context dependencies. Furthermore, the identified dichotomy of disturbance effects on the turnover in community composition demonstrates the potential of disturbances to either stabilize or destabilize biodiversity patterns over time across a wide range of environmental conditions.
Article
Coastal salt marshes are distributed widely across the globe and are considered essential habitat for many fish and crustacean species. Yet, the literature on fishery support by salt marshes has largely been based on a few geographically distinct model systems, and as a result, inadequately captures the hierarchical nature of salt marsh pattern, process, and variation across space and time. A better understanding of geographic variation and drivers of commonalities and differences across salt marsh systems is essential to informing future management practices. Here, we address the key drivers of geographic variation in salt marshes: hydroperiod, seascape configuration, geomorphology, climatic region, sediment supply and riverine input, salinity, vegetation composition, and human activities. Future efforts to manage, conserve, and restore these habitats will require consideration of how environmental drivers within marshes affect the overall structure and subsequent function for fisheries species. We propose a future research agenda that provides both the consistent collection and reporting of sources of variation in small-scale studies and collaborative networks running parallel studies across large scales and geographically distinct locations to provide analogous information for data poor locations. These comparisons are needed to identify and prioritize restoration or conservation efforts, identify sources of variation among regions, and best manage fisheries and food resources across the globe.
Article
Triatoma infestans (Hemiptera, Reduvidae) is the main vector of Chagas disease in South America between the latitudes 10° and 46° S. The analysis of the spatial genetic structure of populations at fine scale can provide insight into the dynamic population and evolutionary process of T. infestans and a complementary approach to help improve vector control strategies. Spatio‐temporal analysis of the genetic structure of T. infestans populations was performed using inter‐simple sequence repeats markers. A total of 242 polymorphic bands were detected from 234 individuals captured in different houses from the locality of San Martín and in one surrounding area (Capayan department, Catamarca province, Argentina) in October 2007 and May 2010. Significant levels of genetic differentiation were detected among the collection sites in both temporal samples, including the different sampled sites within the same house. These results confirm a high degree of subdivision in T. infestans populations. Comparative analysis between the first and the second sample indicated that they form two different groups. The genetic differentiation level was higher among samples from the second capture compared to the first. It is probable that in subdivided populations, when restricted gene flow is sustained over time, the genetic drift leads to accentuate the differentiation among subpopulations. The spatial autocorrelation analysis indicated that the dispersion range could occur around 500–550 m. Therefore, the probability of reinfestation by active dispersal of the insect could be reduced by implementing control and surveillance within an approximate radius of 500–550 m around the infested area. Resumen Triatoma infestans (Hemiptera, Reduvidae) es el principal vector de laenfermedad de Chagas en América del Sur entre las latitudes 10 ° y 46 ° S. Elanálisis temporal de la estructura genética a escala geográfica fina puedeproporcionar información sobre la dinámica y el proceso evolutivo depoblaciones de T. infestans y unenfoque complementario para mejorar las estrategias del control vectorial. Elanálisis espacio‐temporal de la estructura genética de las poblaciones de T. infestans se realizó utilizando marcadoresde secuencias entre repeticiones simples (ISSR). Se detectaron un total de 242bandas polimórficas a partir de los 234 individuos capturados en diferentescasas de la localidad de San Martín y en un área aledaña (departamento deCapayán, provincia de Catamarca, Argentina) en octubre de 2007 y mayo de 2010.Se detectaron niveles significativos de diferenciación genética entre lossitios de recolección en ambas muestras temporales, incluidos los diferentessitios muestreados dentro de la misma casa. Estos resultados confirman un altogrado de subdivisión en las poblaciones de T. infestans. El análisis comparativo entre la primera y la segunda muestraindicó que forman dos grupos diferentes. El nivel de diferenciación genéticafue mayor entre las muestras de la segunda captura en comparación con laprimera. Es probable que en poblaciones subdivididas, cuando el flujo génico restringidose mantiene en el tiempo, la deriva genética conduce a acentuar la diferenciaciónentre subpoblaciones. El análisis de autocorrelación espacial indicó que elrango de dispersión podría ocurrir alrededor de 500 a 550 m. Por lo tanto, laprobabilidad de reinfestación por dispersión activa del insecto podríareducirse implementando el control y la vigilancia dentro de un radio aproximadode 500 a 550 m alrededor del área infestada. In the present work, we compare the fine‐scale spatial genetic structure in two temporal samples of Triatoma infestans from an area without vector control for 31 months. The results suggest that in subdivided populations, where restricted gene flow is sustained over time, the genetic drift could accentuate the differentiation among subpopulations. Spatial analysis suggests a dispersion range around 550 m. Reinfestation by active dispersal could be reduced by implementing control within a radius of 550 m around the infested area.
Article
Grazing by all members of an herbivore community can act to structure the ecosystems they feed on. The outcome of this grazing pressure on the plant community also depends on the interaction between different herbivore groups that are present. We carried out a three-month multi-level field exclusion experiment to understand how different groups of herbivores act both individually and interactively to structure a subtropical seagrass meadow in the Great Barrier Reef. Megaherbivore grazing had the largest impact on this seagrass meadow, significantly reducing aboveground biomass and shoot height, whereas there was no measurable impact of meso-or macroherbivores on seagrass metrics or epiphyte biomass. Megaherbivores here grazed broadly across the meadow instead of targeting grazing in one area. The principal seagrass-herbivore dynamic in this meadow is that megaherbivores are the main group modifying meadow structure, and other grazer groups that are present in lower numbers do not individually or interactively structure the meadow. We demonstrate that herbivory by large grazers can significantly modify seagrass meadow characteristics. This has important implications when designing and interpreting the results of monitoring programs that seek to conserve seagrass meadows, the ecosystem services that they provide and the herbivores that rely on them. Collectively, our results and those of similar previous studies emphasize there is unlikely to be one seagrass and herbivory paradigm. Instead, for individual meadows, their unique species interactions and differences in biotic and abiotic drivers of seagrass change are likely to have a strong influence on the dominant seagrass-herbivore dynamic.
Preprint
Plant-associated microorganisms are essential for their hosts' survival and performance. Yet, most plant microbiome studies to date have focused on terrestrial plant species sampled across relatively small spatial scales. Here we report results of a global-scale analysis of microbial communities associated with leaf and root surfaces of the marine eelgrass Zostera marina throughout its range in the Northern Hemisphere. By contrasting host microbiomes with those of their surrounding seawater and sediment communities, we uncovered the structure, composition and variability of microbial communities associated with Z. marina . We also investigated hypotheses about the mechanisms driving assembly of the eelgrass microbiome using a whole-genomic metabolic modeling approach. Our results reveal aboveground leaf communities displaying high variability and spatial turnover, that strongly mirror their adjacent coastal seawater microbiomes. In contrast, roots showed relatively low spatial turnover and were compositionally distinct from surrounding sediment communities — a result largely driven by the enrichment of predicted sulfur-oxidizing bacterial taxa on root surfaces. Metabolic modeling of enriched taxa was consistent with an assembly process whereby similarity in resource use drives taxonomic co-occurrence patterns on belowground, but not aboveground, host tissues. Our work provides evidence for a core Z. marina root microbiome with putative functional roles and highlights potentially disparate processes influencing microbiome assembly on different plant compartments.
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Knysna estuarine bay in South Africa's Garden Route National Park is that country's most significant estuarine system for biodiversity and conservation value. One outstanding feature is support of 40% of South Africa's—and maybe 20% of the world's—remaining vulnerable and decreasing dwarf-eelgrass, Zostera capensis, whose associated benthic macrofauna has been studied since 2009. For these invertebrates, Knysna comprises several significantly different compartments: sandy mouth; well-flushed marine embayment; poorly flushed central sea-water 'lagoon'; and two disjunct but faunistically similar peripheral regions–marine backwater channels, and low-salinity upper estuary. Although macrofauna ranges from dilute brackish to fully marine, its abundance, local patchiness, and over considerable stretches, species density remains remarkably constant; further, one-third of species occur throughout. Intertidally, all but peripheral compartments are low density and infaunally dominated, while some peripheral areas, and much of the subtidal, are higher density and epifaunally dominated. Overall, seagrass macrobenthos appears maintained below carrying capacity (e.g., by abundant juvenile fish) and of random species composition within a site. Two further characteristics are notable: Unusually, seagrass supports fewer animals than adjacent unvegetated areas, probably because of lack of bioturbatory disturbance in them, and the vegetation cover may ameliorate ambient habitat conditions. Unfortunately, continual heavy and effectively unpreventable exploitation for bait occurs, and chlorophyte blooms have developed because of high nutrient input. Knysna presents a microcosm of problems facing biodiverse and high-value habitats set within areas of high unemployment where subsistence fishing provides the main source of protein and seagrass provides the only source of bait.
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Thesis
Ce travail de thèse s’appuie sur les données d’un suivi à long-terme mené à une échelle régionale pour mieux appréhender les facteurs gouvernant la diversité des fonds marins côtiers. En considérant de multiples échelles spatiales et temporelles ainsi que différentes facettes de la diversité de ces communautés, l’objectif principal a été de fournir des connaissances permettant de mieux prédire les potentielles réponses des communautés benthiques face aux changements environnementaux à venir. Cette thèse s’inscrit en particulier dans un contexte de la menace de l’homogénéisation des fonds marins et de la disparition à large échelle des habitats biogéniques, réservoirs de biodiversité formés par des espèces fondatrices. La comparaison de deux de ces habitats, les herbiers de Zostères intertidaux et les bancs de mäerl subtidaux, à des sédiments dépourvus d’espèces fondatrices a mis en évidence le rôle fondamental de ces habitats biogéniques dans le maintien de la diversité et du fonctionnement des fonds marins à long-terme. Ils contrôlent profondément les dynamiques temporelles des communautés et leurs capacités de réponse aux variations des conditions environnementales, assurent une plus grande stabilité des structures spatiales des communautés à une échelle régionale. Ils semblent par-là essentiels au maintien à long-terme des fonctions écologiques auxquelles contribuent les espèces benthiques. Cependant, ce travail montre que ces espèces fondatrices opèrent selon des mécanismes différents et que les implications en terme de vulnérabilité des communautés sont donc aussi différentes. Cette étude montre enfin qu’au sein d’un habitat donné, la richesse locale des communautés est relativement stable dans l’espace et le temps et met en évidence le besoin de caractériser les variations de compositions de communautés pour guider les actions de conservations à larges échelles. À ce titre, et à l’échelle régionale, les variations de composition contribuent à une richesse taxinomique et fonctionnelle dans les sédiments dépourvus d’espèces fondatrices aussi importante que dans les habitats biogéniques.Ce résultat impose de réévaluer la valeur de conservation qui pourrait leur être attribué de part leur richesse locale limitée. Les suivis à grandes échelles spatiales et temporelles sont dans ce contexte essentiels pour fournir un lien entre les connaissances empiriques et théoriques existantes à des échelles locales, et les échelles supérieures auxquelles s’intéressent les politiques de conservation.
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The nine species comprising the genus Zostera discussed in this chapter form a widespread and relatively well-studied group of seagrasses. Some of the earliest studies of seagrasses occurred within the genus Zostera, especially the extensively researched Zostera marina L. (Petersen, 1890, 1918). The proximity of this species to industrialized areas and centers of scientific investigation in North America, Europe, and Asia has encouraged a continued scientific focus. Like all seagrasses, those of the genus Zostera live in intertidal and subtidal inshore waters, forming a critical habitat and a basis of the foodweb. Study of the genus Zostera is itself representative of trends in seagrass science, with PAM fluorometry assessments of photosynthesis and genetic investigations among the newer efforts.We here review the current knowledge of this important genus, although space constraints do not allow exhaustive coverage of all past and current Zostera research.We also point to future research directions.
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In coastal marine food webs, small invertebrate herbivores (mesograzers) have long been hypothesized to occupy an important position facilitating dominance of habitat-forming macrophytes by grazing competitively superior epiphytic algae. Because of the difficulty of manipulating mesograzers in the field, however, their impacts on community organization have rarely been rigorously documented. Understanding mesograzer impacts has taken on increased urgency in seagrass systems due to declines in seagrasses globally, caused in part by widespread eutrophication favoring seagrass overgrowth by faster-growing algae. Using cage-free field experiments in two seasons (fall and summer), we present experimental confirmation that mesograzer reduction and nutrients can promote blooms of epiphytic algae growing on eelgrass (Zostera marina). In this study, nutrient additions increased epiphytes only in the fall following natural decline of mesograzers. In the summer, experimental mesograzer reduction stimulated a 447% increase in epiphytes, appearing to exacerbate seasonal dieback of eelgrass. Using structural equation modeling, we illuminate the temporal dynamics of complex interactions between macrophytes, mesograzers, and epiphytes in the summer experiment. An unexpected result emerged from investigating the interaction network: drift macroalgae indirectly reduced epiphytes by providing structure for mesograzers, suggesting that the net effect of macroalgae on seagrass depends on macroalgal density. Our results show that mesograzers can control proliferation of epiphytic algae, that top-down and bottom-up forcing are temporally variable, and that the presence of macroalgae can strengthen top-down control of epiphytic algae, potentially contributing to eelgrass persistence.
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We propose an integrated sampling, rarefaction, and extrapolation methodology to compare species richness of a set of communities based on samples of equal completeness (as measured by sample coverage) instead of equal size. Traditional rarefaction or extrapolation to equal-sized samples can misrepresent the relationships between the richnesses of the communities being compared because a sample of a given size may be sufficient to fully characterize the lower diversity community, but insufficient to characterize the richer community. Thus, the traditional method systematically biases the degree of differences between community richnesses. We derived a new analytic method for seamless coverage-based rarefaction and extrapolation. We show that this method yields less biased comparisons of richness between communities, and manages this with less total sampling effort. When this approach is integrated with an adaptive coverage-based stopping rule during sampling, samples may be compared directly without rarefaction, so no extra data is taken and none is thrown away. Even if this stopping rule is not used during data collection, coverage-based rarefaction throws away less data than traditional size-based rarefaction, and more efficiently finds the correct ranking of communities according to their true richnesses. Several hypothetical and real examples demonstrate these advantages.
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Forests are of major importance to human society, contributing several crucial ecosystem services. Biodiversity is suggested to positively influence multiple services but evidence from natural systems at scales relevant to management is scarce. Here, across a scale of 400,000 km(2), we report that tree species richness in production forests shows positive to positively hump-shaped relationships with multiple ecosystem services. These include production of tree biomass, soil carbon storage, berry production and game production potential. For example, biomass production was approximately 50% greater with five than with one tree species. In addition, we show positive relationships between tree species richness and proxies for other biodiversity components. Importantly, no single tree species was able to promote all services, and some services were negatively correlated to each other. Management of production forests will therefore benefit from considering multiple tree species to sustain the full range of benefits that the society obtains from forests.
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Individual scientists, scientific organizations, and government agencies have all concluded that eutrophication is among the most detrimental of all human activities in coastal ecosystems; very large amounts of funding have been earmarked to study the negative consequences of nutrient pollution. Most studies of eutrophication have been conducted long after the numbers and diversity of larger marine consumers were dramatically reduced by centuries of intense harvesting. It is now understood that these once abundant predators played pivotal roles in regulating ecosystem structure and function, and that the widespread overharvesting of large consumers can trigger indirect effects that alter species compositions in ways that are very similar to those reported to result from eutrophication. All of this suggests that we should reevaluate whether the many negative effects attributed to eutrophication are actually a result of nutrient additions or whether they may be the result of the indirect effects of dramatically altered coastal food webs. In this essay, we review experimental assessments of the degree to which changes in consumer abundances have indirectly altered the structure of benthic ecosystems in coastal waters, and on the relative importance of top-down and bottom-up effects on coral reefs, rocky shores, and seagrass meadows. We find that the evidence clearly indicates that indirect consumer effects are the primary drivers of coastal benthic ecosystem structure and function.
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The nine species comprising the genus Zostera discussed in this chapter form a widespread and relatively well-studied group of seagrasses. Some of the earliest studies of seagrasses occurred within the genus Zostera, especially the extensively researched Zostera marina L. (Petersen, 1890, 1918). The proximity of this species to industrialized areas and centers of scientific investigation in North America, Europe, and Asia has encouraged a continued scientific focus. Like all seagrasses, those of the genus Zostera live in intertidal and subtidal inshore waters, forming a critical habitat and a basis of the foodweb. Study of the genus Zostera is itself representative of trends in seagrass science, with PAM fluorometry assessments of photosynthesis and genetic investigations among the newer efforts.We here review the current knowledge of this important genus, although space constraints do not allow exhaustive coverage of all past and current Zostera research.We also point to future research directions.
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Evidence is mounting that extinctions are altering key processes important to the productivity and sustainability of Earth's ecosystems. Further species loss will accelerate change in ecosystem processes, but it is unclear how these effects compare to the direct effects of other forms of environmental change that are both driving diversity loss and altering ecosystem function. Here we use a suite of meta-analyses of published data to show that the effects of species loss on productivity and decomposition--two processes important in all ecosystems--are of comparable magnitude to the effects of many other global environmental changes. In experiments, intermediate levels of species loss (21-40%) reduced plant production by 5-10%, comparable to previously documented effects of ultraviolet radiation and climate warming. Higher levels of extinction (41-60%) had effects rivalling those of ozone, acidification, elevated CO(2) and nutrient pollution. At intermediate levels, species loss generally had equal or greater effects on decomposition than did elevated CO(2) and nitrogen addition. The identity of species lost also had a large effect on changes in productivity and decomposition, generating a wide range of plausible outcomes for extinction. Despite the need for more studies on interactive effects of diversity loss and environmental changes, our analyses clearly show that the ecosystem consequences of local species loss are as quantitatively significant as the direct effects of several global change stressors that have mobilized major international concern and remediation efforts.
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The most unique feature of Earth is the existence of life, and the most extraordinary feature of life is its diversity. Approximately 9 million types of plants, animals, protists and fungi inhabit the Earth. So, too, do 7 billion people. Two decades ago, at the first Earth Summit, the vast majority of the world's nations declared that human actions were dismantling the Earth's ecosystems, eliminating genes, species and biological traits at an alarming rate. This observation led to the question of how such loss of biological diversity will alter the functioning of ecosystems and their ability to provide society with the goods and services needed to prosper.
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GENCLONE 1.0 is designed for studying clonality and its spatial components using genotype data with molecular markers from haploid or diploid organisms. GENCLONE 1.0 performs the following tasks. (i) discriminates distinct multilocus genotypes (MLGs), and uses permutation and resampling approaches to test for the reliability of sets of loci and sampling units for estimating genotypic and genetic diversity (a procedure also useful for nonclonal organisms); (ii) computes statistics to test for clonal propagation or clonal identity of replicates; (iii) computes various indices describing genotypic diversity; and (iv) summarizes the spatial organization of MLGs with adapted spatial autocorrelation methods and clonal subrange estimates.