PROTOZOAN NUMBERS AND BIOMASS IN THE SEDIMENTS OF THE BLAKE OUTER RIDGE

Numbers and biomass of protozoans from the top centimetres of sediment were estimated from four box cores, one taken at 135 m on the shelf and the other three along the crest (2411-3833 m water depth) of the Blake Outer Ridge (BOR). The mean numbers of protozoans ranged from 165 to 964 cm-3, and biomass estimates ranged from 2.2 to 33 x 10(-4) mg cm-3. The lowest numbers and smallest biomass were found at the shelf station. Protozoan biomass along the BOR was an order of magnitude greater, ranging from 2.0 to 3.3 x 10(-3) mg cm-3, while total numbers ranged from 347 to 964 cm-3. Ciliates dominated at almost all depths but showed no trend with depth. Amoebas increased and flagellates decreased with depth. Based on variance to mean ratios for these samples, the benthic protozoan population has a clumped distribution. We found no relation of protozoan numbers with sediment bacterial numbers, porosity of the surface sediments, and per cent total organic carbon of the sediments.