Dispersal Strategies of the Biota on an Oceanic Seamount: Implications for Ecology and Biogeography.

Cobb Seamount lies at 46{deg} 46'N, 130{deg} 48'W in the northeast Pacific 510 km due west of the Oregon coast. The isolated seamount rises 3000 m in a current field flowing from west to east. The seamount supports dense populations of fish and benthos. Collections and submersible observations of the benthic community produced a list of 117 species representing 13 phyla. The organisms present can nearly all be found on the North American Pacific coast, but the diversity is low. This paper presents an analysis of the larval dispersal modes of the benthos at Cobb Seamount. This remote seamount is dominated by species with either a short-lived or no planktonic larval phase. The preponderance of such larval strategies and the observation of abundant drifting kelp near the seamount suggest that rafting of adults may be an effective dispersal mode. The presence of a recirculating flow in the form of a modified Taylor cap appears important for trapping short-lived larvae on the seamount. However, because the water mass is replaced about every 17 days, medium and long-lived larvae would not be retained. The interplay between local currents, available dispersal vectors, and life-history strategies cannot be overlooked in the interpretation of marine biogeographic patterns.