Ecology of deep-sea nematodes from the Puerto Rico trench area and Hatteras Abyssal plain

Abstract

Nematode assemblages from a bathyal silty-sand and three hadal silty-clays from the Puerto Rico Trench area were compared with that from a silty-clay from the HatterasAbyssal Plain. Fine sediments at each site were largely dominated by species belonging to three major genera: Theristus, Acantholaimus and Halalaimus. At the bathyal sand site the relative abundances of these genera were reduced and those of several others (e.g. Desmodora, Leptolaimus, Camacolaimus, Tricoma, Greeffiella, Setoplectus) elevated. Average body weight of nematodes occurring in the sand was 0.057 μg (dry weight), approximately 20–50% that of the nematodes found in the silty-clays. It is suggested that in the deep sea, as at shallow depths, smaller nematodes are better able to move in heterogeneous, coarser sediments than in more uniform, fine ones. Deposit-feeding species were the dominant feeding type observed in all sediments, but epistrate feeders were most numerous in the bathyal sands, probably the result of increased resource partitioning by worms inhabiting a more heterogeneous sedimentary environment. Species richness in bathyal sands was also high. Normal classification of assemblages found in sediments from the Hatteras Plain, Puerto Rico Trench areas, Venezuela Basin and upper abyssal province off North Carolina suggests that deep-sea nematode families and genera are widely distributed across the Antillean Arc. However, species endemism is high: 67 and 77% of the species identified from the Hatteras Plain and Puerto Rico Trench respectively, occurred only at these sites. Affinities among species from all four sites were very low. The wide distribution of families and genera, and narrow distribution of species, suggests that current radiation of deep-sea nematodes probably occurs at the species level.