Photographic observations of deep-sea infaunal ophiuroids in Suruga Bay, central Japan: an application of a free-fall system of time-lapse cameras and current meters

Abstract

Underwater observations of infaunal amphiurid ophiuroids were made at a depth of about 480 m in Suruga Bay, central Japan, using a free-fall system which consists of time-lapse stereo-photography units and current meters. The megabenthos fauna was characterized by the dominance of infaunal echinoderms; in particular, amphiurid ophiuroids were numerically dominant. The density and biomass of the amphiurids were 170 m−2 and 37 g m−2, respectively. They buried their discs in the sediment and extended their arm tips out of the sediment surface. They protruded 2.2 arms per individual on the average. Strong bottom currents were observed, and the average velocity was 12 cm sec−1 at 4 m above the sea floor. No arm tip was observed to be raised vertically into the water column for suspension feeding utilizing the bottom current, and amphiurids were considered to be primarily a surface deposit feeder at the present site.