Harpacticoid copepods are successful in the soft-bottom deep sea

Different taxa have had different degrees of success in invading and prolif erating in the deep sea. The reasons for these differences are not well kno wn, and exemplars need to be studied to provide insight as to factors that lead to success in the deep sea. Because the abundance of the deep-sea faun a taken as a whole declines with depth, the absolute abundance of a taxon i s not an appropriate metric of its success. Rather, a taxon whose abundance declines as rapidly as or less rapidly than the general trend should be co nsidered successful. In this paper, I used the macrofauna to define the gen eral trend of abundance change with depth. When I compared the trend of abu ndance of harpacticoids to that for macrofauna, I found that harpacticoid a bundance decreased less rapidly. Thus, harpacticoids are unusually successf ul in the deep sea. The reasons for their success are unknown, but I discus s three possible explanations.