Metacommunity dynamics of seagrass meadows: Linking local and regional diversity of invertebrate mesograzers

Background/Question/Methods

Many terrestrial habitats are spatially structured and contain species whose dispersal distance exceeds the spatial extent of local habitat patches. In these systems, metacommunity processes (e.g. dispersal, trophic interactions) contribute to spatial and temporal patterns of community assembly. Likewise, many marine systems that are structured by foundation species (e.g. kelp forests, coral reefs, and seagrass meadows) have similar spatial variation in habitat distribution and species dispersal. However, the importance of metacommunity dynamics in structuring marine faunal communities is not well understood. Here, we studied epifaunal mesograzer communities in seagrass meadows of British Columbia, Canada. Like other marine habitats, seagrass meadows support a productive food web involving many mobile consumers, and metacommunity processes could be important in determining energy flow through the ecosystem. We used spatially hierarchical and temporally replicated field surveys to quantify invertebrate communities within and among meadows. Specifically, we addressed the following questions: 1) How does spatial and temporal assembly of epifaunal community composition vary within and among meadows? 2) Is spatial and temporal variation in community structure explained by abiotic factors? 3) Does beta diversity of epifaunal species correspond to functional diversity among meadows?  

Results/Conclusions

Epifaunal community composition varies both spatially and temporally within and among meadows, demonstrating unique community trajectories for each site over the course of the summer. Additionally, regional gamma diversity decreased, while beta diversity increased indicating that local epifaunal communities became less heterogeneous as different grazers became dominant at different sites. The regional species pool experienced less temporal species turnover overall than the average meadow. This suggests that regional diversity is more stable than local species composition. Beta diversity analysis coupled with the turnover of species through time supported the possibility that epifaunal mesograzers are not dispersal limited in seagrass meadows. This spatial and temporal community structure may mitigate the impacts of habitat destruction and climate change up to a point, allowing epifaunal recolonization of disturbed meadows from other meadows. However, the loss of species-source patches may also result in the extinction of key mesograzers in meadows that serve as species-sinks or refuges. This suggests that species persistence may require more patches than expected based on a model of persistent local populations, as higher beta diversity reduces redundancy of epifauna among meadows.