Mid-lower bathyal benthic foraminifera of the Campos Basin, Southeastern Brazilian margin: Biotopes and controlling ecological factors

The benthic foraminiferal assemblages recovered from 41 surface sediment samples of the Campos Basin, southeastern Brazilian continental margin, were analyzed in order to understand their distribution patterns and ecological preferences. Living and dead specimens of benthic foraminifera were selected for identification and quantitative analysis from the 63 to 125 μm, the > 125 μm and the combined > 63 μm size fractions. Q-mode cluster and canonical correspondence analyses for all size fractions show the dissimilarity between the samples collected on the middle slope (Group 1: 750 to 1050 m water depth) and those collected on the lower slope (Group 2: 1350 to 1950 m water depth). Food supply, energy state (stability) at the benthic/pelagic boundary and the grain size of the substrate seem to be the most important environmental factors determining the distribution pattern of the benthic foraminiferal assemblages in the deep sea. The middle slope (between 750 and 1050 m water depth) is characterized by the dominance of different species of the genus Bolivina, Cassidulina laevigata and Globocassidulina subglobosa. The occurrence of these species in association with Cibicidoides kullenbergi, Epistominella exigua and Uvigerina proboscidea seems to be related to seasonal organic matter fluxes, relatively oxic bottom waters, strong bottom currents and sandy sediments. The lower slope (between 1650 and 1950 m water depth) is inhabited by a microfauna with different characteristics, composed of preferentially epifaunal or shallow infaunal deposit feeding species (e.g., Bolivina spp., Eponides weddellensis, Lenticulina cultrata) and suspension feeders that are adapted to oligotrophic conditions and high dissolved oxygen levels in the bottom waters (e.g., Rhabdammina spp., Rhizammina sp.).