Mobile megafaunal activity monitored with a time-lapse camera in the abyssal North Pacific

Abstract

Epibenthic megafauna comprise a large fraction of the deep-sea benthic biomass and are considered important in bioturbation and sediment mineralization processes. However, the sparse and often patchy distribution of these animals makes them difficult to study on meaningful spatial and temporal scales. We used a new time-lapse camera system to measure 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 in a tripod frame with a field marker, time releases and flotation assembly. Time-lapse photographs of the sea floor were taken hourly from March to June 1991 at a station off the central California coast (34°50′N, 123°00′W) at a depth of 4100 m. Megafaunal density reached a peak in April, immediately preceding inceased fluxes of particulate organic carbon (POC) and chlorophyll a measured in sediment traps at 50 m above bottom. Mobile megafauna were numerically dominated by the holothuroids, Abyssocucumis abyssorum, Peniagone vitrea and Elpidia minutissima. The total area traversed by the megafauna each day was estimated by summing the distance traveled between hourly photographs multiplied by the body width of each animal. Area traversed by the megafauna reached a peak in early May following the peak in faunal density and preceding the peak in POC flux in mid-May. The mobile megafauna traversed 88% of the 20 m 2 area of the sea floor over the 3-month period. Estimates of oxygen consumption for the dominant mobile megafauna revealed that these animals would consume only 1.6% of the particulate organic carbon flux entering the benthic boundary layer. However, the extensive area traversed by the mobile megafauna in a 3-month interval suggests that these animals are important as modifiers of the surface sediment, either through mixing or repackaging of material.