Diversity and microhabitats of living benthic foraminifera in the abyssal Northeast Pacific

We investigated assemblages of living benthic foraminifera (>63 mu m) from replicate samples at Station M in the abyssal Northeast Pacific. Push cores collected in September 2007 (StatM07) and May 2009 (StatM09) from 3953 m depth were examined for population densities, species composition, and vertical occurrence within the sediment. Analysis of rose Bengal-stained (StaM09) and cytoplasm bearing (StaM07) foraminifera revealed average total abundances in the top 1 cm of 284 ind./10 cm(3) (StaM07) and 365 ind./10 cm(3) (StaM09). At both sites monothalamous saccamminids were numerically abundant, at StM09 they dominated the 1-2 cm interval and at StaM07 they dominated at all depths. Calcareous taxa were numerically least abundant, while agglutinated foraminifera displayed the highest number of species. The occurrence of few abundant and many rare species resulted in diversity measures for StaM09 (H' 3.3, alpha 17.9) and StaM07 (H' 2.6, alpha 15.2). Numbers of individuals peaked at the sediment surface and declined with sediment depth; living specimens present down to 5 cm depth. The majority of species displayed an epifaunal or shallow-infaunal habitat The observed vertical distribution patterns, species diversity, and assemblage composition are similar to other abyssal North Pacific assemblages and reflect the level of organic flux at Station M.