Activity patterns of mobile epibenthic megafauna at an abyssal site in the eastern North Pacific: results from a 17-month time-lapse photographic study

Abstract

Mobile epibenthic megafauna are important components of many deep-sea communities, yet direct observations of their activities and estimates of their potential impact on benthic processes are scarce. To address this deficiency we deployed a time-lapse camera system at an abyssal site in the eastern North Pacific (Sta. M; 34°50′N, 123°00′W; 4100 m depth) to monitor epibenthic megafaunal movements over the 17-month period from February 1990 through July 1991. Photographs, each covering approximately 20 m 2, were taken every hour during this time span, except for the period from late October 1990 through mid-February 1991, when photos were taken every 4 h. Movements of the seven numerically dominant species of mobile epibenthic megafauna were digitized and analyzed for spatial patterns and temporal variation. These movements were markedly non-random for all seven species, with movement patterns falling into three broad categories: run-and-mill, loop and run. The holothuroid Peniagone vitrea displayed looping behavior that in some cases ( n = 8) had a distinct, semi-diurnal component possibly attributable to the influence of external factors such as tidal currents. P. vitrea was also the only species of the seven observed to swim. Temporal variations in movement patterns were also observed, with individuals of the two most abundant species, Elpidia minutissima and P. vitrea, spending less time within the camera's field of view during periods when potential food items, in the form of pelagically-derived detrital aggregates, were visible on the sea floor compared to periods when aggregates were absent. Based on abundances, body sizes and movement patterns, the three most abundant species, E. minutissima, P. vitrea and Abyssocucumis abyssorum, traversed 76.5% of the total area of sea floor covered by all seven species between February 1990 and July 1991. Of the seven species we studied, only two, A. abyssorum and Echinocrepis sp., left distinct traces on the sea floor. These two species accounted for only 32.8% of the total area of sea floor traversed by the mobile megafaunal community at Sta. M. Collectively, the seven numerically dominant species of mobile epibenthic megafauna at Sta. M traversed ca 36 m 2 of sea floor per year within the field of view of our time-lapse camera system ( ca 20 m 2). Our results indicate that mobile epibenthic megafauna have the potential to substantially impact benthic processes at Sta. M, particularly processes involving the utilization, processing and redistribution of particulate organic material at the sea floor.