FINE-SCALE VERTICAL PROFILES OF MEIOFAUNA IN MUDDY SUBTIDAL SEDIMENTS

The fine-scale vertical profile (2-mm intervals to 2 cm) of meiofauna was surveyed at three water depths (20, 50, and 80 m) on the Louisiana continental shelf and at two depths (25 and 55 m) in a subarctic Alas kan bay. Meiofaunal densities at these sites measured through 4 cm wer e similar to those of other subtidal muddy-sediment sites, nematodes a veraging about 1000 and 1500 and harpacticoid copepods averaging 125 a nd 30 per 10 cm(2) in Louisiana and Alaska, respectively. Overall, har pacticoids were numerous at the sediment-water interface and exception ally shallow in depth profile; densities decreased with increasing dep th, with few individuals below 6 mm. Across all sites and water depths , weighted mean depths of harpacticoids averaged 5.4 mm. Nematodes wer e distributed to much greater depths, and generally increased in densi ty with depth, with highest densities below 6 mm. In the Gulf of Mexic o, nematode density peaked in the second centimetre. Across all sites and depths, nematode weighted mean depth averaged 10.5 mm within the u pper 2 cm. Harpacticoids were the most abundant meiofaunal taxon in th e upper 4 mm in the Gulf of Mexico at the 50- and 80-m sites. Overall, harpacticoids were disproportionately abundant at the sediment-water interface to a depth of 6 mm, and play a more significant role in even ts that take place at the surface than their down-core abundance would indicate. For example, harpacticoids are potentially more influenced by bottom-feeding fish and erosional events than are nematodes, and ma y exert an influence over the initial burial of sedimented phytodetrit us.