Eelgrass‐associated invertebrate biodiversity patterns in a subarctic seascape

Abstract

Abiotic, biotic, and spatial processes shape patterns of biodiversity in coastal ecosystems. In this study, we test how these processes influence eelgrass‐associated invertebrate diversity in a subarctic seascape. We sampled invertebrate assemblages in 12 meadows along 300 km of coastline in James Bay, Canada, and tested the relative contributions of abiotic conditions, spatial arrangement, and meadow attributes in explaining variation in invertebrate community composition, abundance, and diversity within and among meadows. We found that eelgrass meadows in James Bay support diverse invertebrate communities comprising at least 72 taxa. Greater invertebrate abundance was associated with higher epiphyte load and clearer water (lower turbidity). Invertebrate diversity increased with aboveground eelgrass biomass and epiphyte loads, and species richness increased in clearer water. Invertebrate communities in very salty and very fresh waters contributed the most to regional beta diversity. Variation in taxonomic composition across the seascape was notable; no species was observed at every site, and most taxa were observed at 3–5 sites. The most widely distributed taxa were the arctic amphipod Gammarus setosus and the bivalves Mytilus trossulus and Macoma balthica , each observed at 11 of the 12 sites. Variation in taxonomic composition among meadows was partially explained by meadow spatial arrangement and local abiotic conditions (salinity, fetch, temperature, and turbidity) but not meadow attributes such as eelgrass biomass or shoot size. We conclude that both local conditions and regional ecological processes such as spatially structured population dynamics and species interactions may be important for regional‐scale biodiversity patterns on this coastline.

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