The benthic fauna of the Rockall Trough: regional distribution and bathymetric zonation

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Abstract
Synopsis: More than 300 bottom samples taken in the Rockall Trough and neighbouring areas (Northeast Atlantic) since 1973 provide an opportunity to study the distributions of the commoner megafaunal species. These include 131 species of echinoderms, for the most abundant of which the bathymetric and regional distributions are defined. Analysis of samples by means of the coincidence-of-range method along a bathymetric transect shows peaks-in the first and last occurrences of species at the 800–1200m and 1800 m levels. Cumulative curves of the recruitment of all echinoderm species with increasing depth show step-like increases in the rate of species recruitment with depth. These maxima in rate of faunal change are related to water–mass structure, particularly the depth of the seasonal and permanent thermoclines. A considerably broader bathymetric range is shown by post-larvae and juvenile stages compared to adults.