DISPERSAL STRATEGIES OF THE BIOTA ON AN OCEANIC SEAMOUNT - IMPLICATIONS FOR ECOLOGY AND BIOGEOGRAPHY

Cobb Seamount lies at 46 degrees 46'N, 130 degrees 48'W in the northea st Pacific 510 km due west of the Oregon coast. The isolated seamount rises 3000 m in a current held flowing from west to east. The seamount supports dense populations of fish and benthos. Collections and subme rsible observations of the benthic community produced a list of 117 sp ecies representing 13 phyla. The organisms present can nearly all be f ound on the North American Pacific coast, but the diversity is low. Th is paper presents an analysis of the larval dispersal modes of the ben thos at Cobb Seamount. This remote seamount is dominated by species wi th either a short-lived or no planktonic larval phase. The preponderan ce of such larval strategies and the observation of abundant drifting kelp near the seamount suggest that rafting of adults may be an effect ive dispersal mode. The presence of a recirculating flow in the form o f a modified Taylor cap appears important for trapping short-lived lar vae on the seamount. However, because the water mass is replaced about every 17 days, medium and long-lived larvae would not be retained. Th e interplay between local currents, available dispersal vectors, and l ife-history strategies cannot be overlooked in the interpretation of m arine biogeographic patterns.