Photographic observations of the brittle star
Ophiura sarsiwere conducted at a depth of approximately 280 m in the Pacific Ocean off Otsuchi, northeastern Japan. Bottom photographs showed that this ophiuroid occurred in high densities, uniformly covering the sea floor and that other megafauna was rare. The mean density and biomass of ophiuroids in the dense bed were estimated to be 373m
-2and 124gm
-2, respectively. Ophiuroids comprised 99% of all megabenthic organisms in terms of number of individuals, and megafauna assemblage of the dense bed showed very low species diversity.
O. sarsiexhibited a regular spatial pattern avoiding contact with conspecific neighbors. This regular spatial pattern was disrupted by certain other organisms, around which halo-like, bare areas were observed. The size and shape of these halo-like areas varied and were apparently related to the body size and/or motility of the organisms. In the present observation area
O. sarsicovered 96% of the sea bottom, and the remaining 4% was occupied by other organisms and their halo-like bare areas.
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