Meiofaunal abundance and vertical zonation in a sublittoral soft bottom, with a test of the Haps corer

Abstract

Total meiofauna abundance was estimated to be 4.7×106 individuals m-2 in a sublittoral soft bottom when sampled by SCUBA diving in the Oresund. Nematode abundance was 4.5×106 (equal to 1.4 g organic carbon), harpacticoid copepods 148×103, kinorhynchs 45×103 and ostracods 28×103·m-2. Three main groups of metabolic types are proposed. Almost all harpacticoid copepods, kinorhynchs and ostracods were found in the uppermost flocculent bottom layer and among the nematodes the non-selective detritus feeding species dominated; nematodes in this layer were mainly small. Epistrate feeding nematodes dominated between 1 and 4 cm depth; the size of nematodes varied greatly (less than 0.1 μl and up to 65 μl) with a mean body volume of 2.6 to 3.7 μl. Non-selective deposit feeding nematodes dominated totally deeper than 4-cm depth, i.e. in and below the redox-potential-discontinuity (RPD) layer. They were of median size and in species composition different from those above 4-cm depth. Haps corer samples underestimated nematode and harpacticoid copepod numbers in the top cm; the abundances were 66 and 48% respectively of those obtained by divers. Therefore, this sampling gear cannot be recommended for meiofauna studies on muddy bottoms covered with a flocculent detritus layer.