MOBILE MEGAFAUNAL ACTIVITY MONITORED WITH A TIME-LAPSE CAMERA IN THE ABYSSAL NORTH PACIFIC

Epibenthic megafauna comprise a large fraction of the deep-sea benthic biomass and are considered important in bioturbation and sediment min eralization processes. However, the sparse and often patchy distributi on of these animals makes them difficult to study on meaningful spatia l and temporal scales. We used a new time-lapse camera system to measu re the movements of mobile megafauna over a 3-month period across a 20 m(2) area of the abyssal sea floor in the eastern North Pacific. This free-vehicle camera system consisted of a time-lapse camera mounted i n a tripod frame with a field marker, time releases and flotation asse mbly. Time-lapse photographs of the sea floor were taken hourly from M arch to June 1991 at a station off the central California coast (34 de grees 50'N, 123 degrees 00'W) at a depth of 4100 m. Megafaunal density reached a peak in April, immediately preceding increased fluxes of pa rticulate organic carbon (POC) and chlorophyll a measured in sediment traps at 50 m above bottom. Mobile megafauna were numerically dominate d by the holothuroids, Abyssocucumis abyssorum, Peniagone vitrea and E lpidia minutissima. The total area traversed by the megafauna each day was estimated by summing the distance traveled between hourly photogr aphs multiplied by the body width of each animal. Area traversed by th e megafauna reached a peak in early May following the peak in faunal d ensity and preceding the peak in POC flux in mid-May. The mobile megaf auna traversed 88% of the 20 m(2) area of the sea floor over the 3-mon th period. Estimates of oxygen consumption for the dominant mobile meg afauna revealed that these animals would consume only 1.6% of the part iculate organic carbon Aux entering the benthic boundary layer. Howeve r, the extensive area traversed by the mobile megafauna In a 3-month i nterval suggests that these animals are important as modifiers of the surface sediment, either through mixing or repackaging of material.