Aspects of the community ecology of deep-sea,benthopelagic plankton,with special attention to gymnopleid copepods

Benthopelagic plankton was collected 10 to 100 m above the bottom of the deep sea (1100 to 3200 m) with an opening-closing net. Five samples were taken from the San Diego Trough, 2 from the eastern tropical Pacific and 2 from the northeast Atlantic. Roughly 80% of the individual organisms collected were copepods; the next most abundant groups were usually isopods, ostracods, and chaetognaths. Within the depth range studied, absolute abundances of most animal groups decreased with depth, but relative abundances (%) did not change. Of over 100 species of adult gymnopleid copepods collected, a few species were abundant, but most were rare. Copepod exoskeletons were more abundant than living copepods. For the gymnopleids, similarities among the 3 geographical regions were strong at the family and genus level but weak at the species level. Species that were widely distributed horizontally tended to occupy different positions (in terms of rank order of abundance) in each community. Gut content analysis indicated that the most abundant gymnopleids were generalized particle feeders. However, size-frequency distributions provided indirect evidence for niche separation. The deep-sea benthopelagic plankton was divisible into a truly planktonic component and a bottom-associated component. Abundances of some copepods changed relative to distance off the bottom. Several copepods and other animals, previously described as epibenthic or bottom-associated, were collected more that 10 m above the bottom and thus appeared to move freely between the bottom and lower water column.