BATHYMETRIC PATTERNS OF DEEP-SEA BENTHIC COMMUNITIES FROM BATHYAL TO ABYSSAL DEPTHS IN THE WESTERN SOUTH-PACIFIC (SOLOMON AND CORAL SEAS)

Ten stations were sampled from bathyal to abyssal depths (695-4350 m) in the Solomon and Coral Seas to determine variations in densities of Protozoa, meiofauna and macroinfauna in relation to environmental conditions and bacterial densities and productivity. Densities of large flagellates and amoebae did not change with water depth, whereas the abundance of other microbenthic groups either decreased (Foraminifera. ciliates) or increased (yeasts) significantly with increasing ocean depth. Numerically, the microbenthos was dominated by Foraminifera, followed in decreasing order of abundance by yeasts, large flagellates. amoeba and ciliates. Densities of total metazoan meiofauna and macroinfauna were low at most stations compared to communities of other regions at equivalent depths. and declined significantly with ocean depth, although many taxa and total macroinfaunal biomass did not. Differences in the rate of decline between total metazoan meiofaunal and macroinfaunal densities with depth were not significant. When the effect of water depth was held constant, only a few protozoan, meiofaunal and macroinfaunal taxa correlated with bacteria and sediment characteristics. Depth-related variables (e.g. low temperatures) appear to be the dominant factors regulating bathymetric patterns. However, there is some evidence that rapid transport of turbidites and other shallow-water materials (wood, vascular plant and fresh algal detritus) lead to episodes of erosion and deposition that may influence the distribution and standing crop of these deep-sea benthic communities. These events may be influential in other tectonically active basins within tropical oceans bordered by steep continental margins and dominated by extensive reefs and large rivers.