The distribution and composition of deep-sea microbenthos in a bathyal region of the western Coral Sea

Abstract

The distribution and composition of bathyal (298–1610 m) microbenthos were examined on the Queensland continental slope, the Coral Sea Plateau and the adjacent Queensland and Townsville troughs in the western Coral Sea. Two conspicuous changes in community composition were recorded: (1) ciliates were undetected below 700 m and (2) yeasts and yeast-like cells were undetected above 1150 m. Densities of flagellates decreased, whereas amoebae densities increased significantly with water depth. Densities of living Foraminifera ( x = 56 cm −2 ) increased significantly from the continental slope to the adjacent troughs. Bacterial numbers ranged from 0.1 to 71.0 × 10 8 cells g −1 dry wt of sediment and decreased significantly with water depth. Chlorophyll a (0.0–19.0 μg g −1 dry wt) and phaeopigment (0.0–4.9 μg g −1 dry wt) concentrations suggest that phytodetritus is a major source of organic matter in this tropical region. Concentrations of organic carbon (0.22–0.52%) and nitrogen (<0.01–0.02%) were low compared to most other deep-sea sediments, with a shallow sediment depth distribution indicating little burial of organic matter. These findings, coupled with the presence of abundant protozoan populations (∼10 6 m −2), suggest the potential for rapid microbial activity and dentrital utilization in bathyal surface sediments of the western Coral Sea.