Bathymetric and spatial distribution of echinoderms on seamounts in the Gulf of Alaska

Abstract

The bathymetric and spatial distribution of echinoderms was examined on five seamounts in the Kodiak-Bowie seamount chain in the northern Gulf of Alaska from video transects of 200 or 500 m length, conducted at approximately 700, 1700 and 2700 m depths with the DSV Alvin in August, 2004. Temperature and salinity varied significantly with depth, but not between seamounts; an oxygen minimum zone encompassed the shallowest depth sampled. Holothuroid (Pannychia and Psolus) and asteroid density for the shallower depth category was 19.94·100 m⁻² and 2.07·100 m⁻², significantly higher than at the deeper depths. Asteroid density generally decreased northwesterly along the seamount chain. Density of three ophiuroid genera (Asteronyx, Amphigyptis, and Ophiomoeris) was 139.6·100 m⁻² on Dickens Seamount, and was significantly less on the other three seamounts to a low of 31.19·100 m⁻² on Pratt Seamount. Ophiuroid density was significantly higher at the intermediate depth (141.07·100 m⁻²), and lower at the other two depths. Density of Pentametrocrinus and Guillecrinus crinoids was not significantly affected by seamount or depth, but was highest (3.15·100 mm⁻²) at the deepest depths. No echinoids were found on transects, but were observed on three of the seamounts. Many brittle stars and asteroids were found associated with paragorgid and primnoid corals.