Benthic Foraminifera of the Blake Ridge hydrate mound, Western North Atlantic Ocean

In a 240 m × 70 m area at the top of the Blake Ridge Diapir (water depth ∼ 2150 m), the benthic foraminiferal assemblage in surface sediment (0–1 cm) consists of about 130 species. Hydrocarbon seepage is indicated here by the presence of methanotrophic bivalves and white bacterial mats, and by present-day formation of gas hydrate. The foraminiferal assemblage density is generally high, indicating an abundance of food. Bolivina lowmani and Globocassidulina subglobosa dominate the assemblage in the silt–clay substrate, whether at the edge of bathymodiolid mussel beds or under bacterial mats. The only notable difference between these two sample groups is in the higher variation of foraminiferal density in the mussel bed samples. A control sample at 32°29.654′ N and 76°11.324 W, taken from bioturbated sediment (light-grey silt and clay with no visible bacterial or molluscan colonization), is comparable to the seep samples in the distribution of calcareous species, but shows a much higher diversity and abundance of agglutinated species. No segregation of foraminiferal species by substrate geochemistry can be inferred for the seep samples, and the possible effect of variable sulfide or methane fluxes on the community cannot be demonstrated by our data.