ECOLOGY OF DEEP-SEA BENTHOS

The benthos of the deep sea in a region between southern New England and Bermuda can be characterized by low density but high within-habitat diversity. The low density is probably determined by the amount of food present and is correlated with depth and distance from land. Depth is the more critical variable. The high diversity, about the same order as that found in shallow tropical seas, can be related to the seasonal and geological stability of the deep-sea environment. An unexpectedly large number of deposit-feeding species are found in individual samples. The composition of the benthic fauna gradually and continuously changes with depth throughout the bathyal and abyssal regions, but an abrupt faunal discontinuity is found at the shelf-slope break in from 100 to 300 meters of water. In this region of our study, the fauna shallower than the zone of discontinuity is eurytopic, of low diversity, and taxonomically distinct from the stenotopic, highly diverse populations living below the discontinuity. In comparing faunal composition, a vertical change of a few hundred meters is equivalent to a change of thousands of kilometers horizontally. The few data on reproduction reveal that some elements of the deep-sea fauna breed continuously, whereas others are restricted to a limited period of the year.