Biogeographical Patterns of Marine Benthic Macroinvertebrates Along the Atlantic Coast of the Northeastern USA

The biogeography of marine benthic macroinvertebrates of US Atlantic estuaries and inshore coastal areas from Delaware Bay north to Passamaquoddy Bay was studied to compare recent data with historical biogeographic studies, define physical–chemical factors affecting species’ distributions, and provide information for calibrating benthic indices of environmental condition. Five years (2000–2004) of data from 614 non-polluted, soft-bottom stations from the National Coastal Assessment were analyzed. Multi-dimensional scaling done on Bray-Curtis similarity matrices of species’ relative abundance (547 species) suggested seven subregions: two based on salinity (oligohaline, mesohaline) and five based on latitude. Species’ distribution patterns for stations with salinities ≥18 (n = 558) were strongly influenced by latitude; Cape Cod was a clear faunal transition zone (R = 0.92, p < 0.001). Conversely, for stations with salinities <18 (n = 56), salinity was the more important factor. An ordination of abiotic variables (temperature, salinity, sediment percent silt-clay, depth) correlated well with the ordination of species’ relative abundance data (R = 0.77, p < 0.001). The first split of a multivariate regression tree was by a summer bottom temperature of 20°C at Cape Cod. Salinity and percent silt-clay led to further splits. These results support the existence of Virginian and Transhatteran biogeographic provinces. They constitute a baseline for addressing broad-scale and long-term issues such as global climate change, species invasions, and conservation planning.