Grab sampling of the subtidal benthic invertebrates was attempted at 50 sites in Lyme Bay, Weymouth Bay and Portland Harbour in May 1994. At several sites the substrate was unsuitable for grab sampling and either no sample was obtained or only a qualitative sample was taken. Data from the 43 sites at which quantitative samples were obtained have been analysed by a variety of statistical techniques to determine similarities between the sites. The area has an extremely diverse fauna; over four hundred taxa were recorded in the samples. Sites had an average of 58 taxa and 286 individuals per grab sample. There was very high variability in the number of taxa per grab sample, ranging from 3 to 158. The majority of taxa and individuals were polychaetes, with crustaceans and molluscs the next most important groups in terms of the number of taxa and individuals respectively. Analysis of the biological data and an examination of the sediment types indicated that four major and three smaller groups (clusters) could be recognised. The biology of each of the clusters is described and related to the underlying sediment type. Fifty sampling positions in the study area were arranged in a rectangular grid pattern, with six major sampling lines running east-west and nine oriented north-south.
