Distribution of <i>Echinarachnius parma</i> (Lamarck) and Associated Fauna on Sable Island Bank, Southeast Canada

Abstract

A combined bottom photographic and sampling survey of Sable Island Bank southeast of Nova Scotia, Canada, reveals locally high densities (to 180 individual/m²) of the northern sand dollar <i>Echinarachnius parma</i>. Populations of this form are closely related to texture of the sea floor and generally concentrated on moderately sorted fine to medium sand surfaces. Topography and current regime are also correlatable factors; depth, time, salinity, and temperature apparently are not. Sand dollars are second in importance, after current activity, in reworking surficial sediments, and these organisms modify at least a third of the total Bank surface in the study area. Bioturbation is particularly intense in the sector north of Sable Island. Associated epifauna and infauna populations occur in two east-west trending areas on the Bank north and south of Sable Island. Absence of conspicuous fauna, save <i>E. parma,</i> in an east-west zone along the crest of the Bank and near Sable Island results from extremely strong current activity concentrated in this region.