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

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 Bri gg), and two moderately sheltered (Selwicks Bay, the sheltered shore at Fil ey Brigg) shores were sampled during one week of spring tides during June 1 996. A total of 6866 individual ostracods comprising of 26 ostracod species were recovered from the algal samples. Some species showed significant dif ferences in abundance with tidal elevation across the four shores, e.g. Hir schmannia viridis was significantly more abundant in the upper shore pools. Other species, e.g. Heterocythereis albomaculata, showed no significant di fference in abundance either with tidal elevation or between shores. Signif icant differences in abundance occurred between shores at a given tidal hei ght in some species, e.g. Semicytherura nigrescens was absent from Selwicks Bay but abundant on the remaining shores. Other species had markedly disju nct distributions, e.g. Callistocythere badia only occurred in the exposed upper shore pools at Filey Brigg. Ostracods were significantly less abundan t in the low shore pools. Cluster analysis showed that low shore samples ha d 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 t he four shores and also between the different tidal elevations.