The vertical distribution of phytal ostracods in the intertidal zone at Gore Point, Bristol Channel, U.K.

Abstract. The first detailed investigation of the vertical distribution of ostracods inhabiting intertidal algae is presented herein. A study was made of the ostracod faunas obtained from samples of Corallina collected at various levels along transects of the intertidal zone at Gore Point in the Bristol Channel. A total of 28 species were recorded, including four new species presently left in open nomenclature. Both the composition of the ostracod fauna and the population age structure of individual species were found to vary considerably according to tidal level. The development of instars apparently proceeds at a faster rate at higher tidal levels, probably due to higher mean annual water temperatures. Among the factors which may determine the percentage composition of the ostracod fauna at a given level are temperature, pH, and the life-cycles and migratory habits of individual species.