Distribution density and relative abundance of benthic invertebrate megafauna from three sites at the base of the continental slope off central California as determined by camera sled and beam trawl

Abstract

Distribution, density and relative abundance of benthic invertebrate megafauna at three sites at the base of the continental slope off central California were investigated by trawls and camera sleds over a two-year period. A total of 29 successful trawls returned a total of 133 species of invertebrates. The dominant taxa by number in the trawls were holothurians, ophiurans, pennatulids, and one species of sea star and one species of corallomorpharian. There was considerable variation in rank order of abundance of the dominant invertebrates among the three sites and within one of the sites between years. Thus the percent similarity among the three sites was also low. Three of the five most abundant species were burrowers and were not detected in the camera sleds. Comparisons of rank order of abundances between the camera sleds and the trawls was done for 18 taxa. Results indicated no significant differences between the two methods and a total percent similarity of 78.8%. Comparison of densities per 100 m 2 between the two methods revealed that the densities estimated from the camera sleds were about 4 times those of the trawls. Reasons for this discrepancy are discussed.