Intertidal ostracod (Crustacea: Ostracoda) abundance and assemblage structure within and between four shores in north-east England

Abstract

Triplicate samples of rockpool algae were collected at each of three tidal elevations (upper, mid and low) from four shores on the north-east coast of England. Two moderately exposed (Ravenscar, the exposed shore at Filey Brigg), and two moderately sheltered (Selwicks Bay, the sheltered shore at Filey Brigg) shores were sampled during one week of spring tides during June 1996. A total of 6866 individual ostracods comprising of 26 ostracod species were recovered from the algal samples. Some species showed significant differences in abundance with tidal elevation across the four shores, e.g. Hirschmannia viridis was significantly more abundant in the upper shore pools. Other species, e.g. Heterocythereisalbomaculata, showed no significant difference in abundance either with tidal elevation or between shores. Significant differences in abundance occurred between shores at a given tidal height in some species, e.g. Semicytherura nigrescens was absent from Selwicks Bay but abundant on the remaining shores. Other species had markedly disjunct distributions, e.g. Callistocythere badia only occurred in the exposed upper shore pools at Filey Brigg. Ostracods were significantly less abundant in the low shore pools. Cluster analysis showed that low shore samples had a high degree of similarity between the four shores whereas the upper and mid-shore samples clustered primarily to shore. A two-way ANOSIM indicated that there was a significant difference in assemblage similarity between the four shores and also between the different tidal elevations.