Mesoscale Spatial Patterns of Gulf of Maine Rocky Intertidal Communities

Community similarity among macroinvertebrate species assemblages from 12 exposed rocky headlands surveyed in 2004, 2007, and 2012 was examined to resolve mesoscale patterns along an east-west linear distance of 366 km in the coastal Gulf of Maine. The goals were: (1) detect latitudinal patterns of species assemblage similarity and (2) relate species assemblage similarities to environmental factors. Assemblage similarities were correlated with latitude. There was a distinguishable grouping of sampling sites fitting two Gulf regions that separate at mid-coast Maine. This pattern was uniquely intertidal and not shown by subtidal species assemblages. beta diversity was high, did not differ between regions, and species turnover accounted for 91% of it. Molluscs and crustaceans, major components of surveyed communities, contributed most of the dissimilarity between regions. Satellite-derived shore and sea surface temperatures explained a significant amount of the variation responsible for producing regional patterns. The regions corresponded with the two principal branches of the Gulf of Maine Coastal Current. These hydrographic features and associated environmental conditions are hypothesized to influence community dynamics and shape the dissimilarity between Gulf regions. The predicted warming of the Gulf of Maine portend change in species turnover from species invasions and range shifts potentially altering rocky intertidal community patterns.