Macroplankton in the near-bottom layer of continental slopes and seamounts

Distributions of mysids, euphausiids, shrimps and bottom-dwelling decapod larvae have been studied to reveal their relation to the sea bottom. A total of about 200,000 specimens belonging to 178 species and closer unidentified taxa has been examined. The material has been taken by R. V. Professor Shtokman in the Southeast Pacific (1987–1988) and by RN. Vityaz in the western Indian Ocean (1989–1990) by sampling at depths of 1500 m and less over seamounts and continental slopes. In addition, aquarium observations on five species and analyses of the gut contents of 14 species have been carried out. Two principal groups of animals have proved to live in the near-bottom layer: pelagic (independent of the bottom) and benthopelagic (related to the bottom). They appear to differ in all studied aspects: distribution, behaviour and feeding. The benthopelagic animals are divided into three subgroups with finer ecological differences: hypo-, epi-, and amphibenthopelagic. The patterns of their distribution and migrations, the near-bottom biological zonation and its relation to the benthic boundary and benthic nepheloid layers are discussed, with (re)definitions of the terms used.