A small hotspot of benthic biodiversity on the northwest Atlantic continental shelf

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The northern edge of Georges Bank supports a highly productive and diverse benthic community. Our study area is the gravel pavement on the Canadian side of Georges Bank in water depths of 72-90 m. This area has been surveyed periodically by Canadian and U.S. researchers because of its importance as fish and scallop habitat. On joint cruises from 1994 to 2005, the substrate has been characterized with side-scan and single-beam sonar. Site-specific sampling has been conducted with photo/video transects, and benthic samplers. Much of the gravel habitat over thousands of square kilometers is disturbed by bottom fishing gear and exhibits relatively low biodiversity. However, in some small areas the gravel has a biogenic covering of colonial epifauna and exhibits high benthic diversity. In one 14 km2 area, dubbed the “mussel bed”, the substrate is almost completely covered with hydroid and bryozoan colonies. This epifaunal habitat contains the highest numerical abundance, biomass, and species richness of benthic megafauna that we have observed on Georges Bank. High benthic productivity in this area is fueled by upwelled waters from the Gulf of Maine. The shelf-edge front moves over the northern edge of the bank such that the water column is well mixed in winter and stratified in summer. The gravel substrate is undisturbed by winter storms, thus providing a stable substrate for mussel and epifaunal growth. This benthic community is vulnerable to potential oil and gas development, bottom-fishing disturbance, and to colonization by invasive species.