Bathyal meiobenthos of the western Coral Sea: distribution and abundance in relation to microbial standing stocks and environmental factors

TLDR: Densities of Foraminifera and other protozoans increased with bathymetric depth, indicating their ability to exploit oligotrophic conditions and to gain numerical dominance in benthic food webs of the deep sea.

Abstract: The distribution and abundance of meiobenthos in relation to microbial densities and environmental factors were examined at 24 stations in a bathyal (298–1610 m) region of the western Coral Sea. Densities of metazoan meiofauna were low (x = 57; range: 19–170 individuals 10 cm−2) compared with other bathyal communtiesm but when densities of living Foraminifera (x = 560; range: 0–3410 individuals 10 cm−2) were included, total faunal densities were high (x = 610 10 cm−2) and ranged from 73 to 3465 individuals 10 cm−2. Soft-bodied (non-chitinous) taxa (e.g. turbellarians) were not detected beyond the continental slope. Densities of all metazoan taxa, excluding nematodes, decreased significantly with bathymetric depth. When the effect of ocean depth was held constant, only a few significant correlations of meiobenthos with microbes and sediment characteristics were found. Our data, coupled with earlier findings of low bacterial densities and organic conditions, suggest that low densities of metazoan meiobenthos in the western Coral Sea are due to low rates of detrital input. However, densities of Foraminifera and other protozoans increased with bathymetric depth (Alongi, 1987, Deep-Sea Research, 34, 1245–1254), indicating their ability to exploit oligotrophic conditions and to gain numerical dominance in benthic food webs of the deep sea.