COS 212-1 - Global analysis of taxonomic and functional diversity in invertebrate communities from intertidal mussel beds

Abstract: Foundation species, such as mussels, are spatially dominant species that create habitat with their body structures and locally limit environmental stress. They are critical in the ecosystems they inhabit due to their ability to host diverse communities. Global information on foundation species and their associated communities can contribute to effective conservation strategies by allowing researchers to predict what lives in understudied communities. Mussels occur on temperate marine rocky shores globally. At high densities, they increase habitat heterogeneity that protects small organisms from various environmental stresses. They also trap biowaste, external detritus, and sedimentary deposits, which ultimately accumulate in the mussel beds providing habitat and food for small organisms. Because of these properties common to mussel beds, we ask: Do mussel beds across the globe provide habitat to similar invertebrate communities? We hypothesized a striking difference in the taxonomic composition of the associated communities among biogeographically distant coasts, but similarities in functional composition. To test these predictions, we compared invertebrate abundance datasets from various sources for mussel beds from rocky shores on the northwest, northeast, southwest, and southeast coasts of the Atlantic and Pacific Oceans.

Our results reveal that, globally, mussel beds host similar numbers of species per unit of substrate area. At the highest taxonomic resolution used by the surveys, geographically distant coasts differed greatly in taxonomic composition. However, at regional scales, some similarities emerged such as between Washington and Oregon (northeast Pacific), Chile and Argentina (southern South America) and eastern Canada and Ireland (northern Atlantic). Remarkably, taxonomic composition overlapped considerably among coasts at a coarser taxonomic resolution. Nine of the 29 taxonomic groups identified were present in at least 80 % of the studied coasts (Polychaeta, Amphipoda, Decapoda, Isopoda, Gastropoda, Anthozoa, Bivalvia, Nemertea, and Cirripedia). Finally, comparisons based on functional traits including trophic level, mobility, and body structure indicated an even higher degree of multivariate overlap among coasts. Twelve of the 14 functional trait categories examined occurred on at least 90 % of coasts. Furthermore, trait category abundances indicated similar regionalities as taxonomic comparisons. These results indicate invertebrate communities from mussel beds share many of the same functions, but they are carried out by different taxa and in different abundances. Overall, this global study reveals the relatively consistent influence mussel beds have on the taxonomic and functional properties of their associated invertebrate communities.