279 Studying the interspecific relationships between the organisms that colonize the surfaces of other ani� mals and plants [13] is currently an urgent ecological problem, because it provides an opportunity for simu� lating the processes occurring in the biological systems of a higher rank [6]. A crustacean shell is a convenient substrate inhab� ited by many invertebrates [11, 14]; since the space accessible for colonizing is limited by the host size, the associated organisms often compete for space. We have previously studied the interspecific relationships in populations of the amphipods Ischyrocerus com� mensalis and I. anguipes [1], which are symbionts of the red king crab Paralithodes camtschaticus of the Barents Sea. Little is known so far about the interspe� cific relationships of the red king crab symbiotic com� munities. In this study, we analyzed these relationships during mass colonizing of the red king crab by inverte� brate symbionts, namely amphipods of the genus Ischyrocerus. The material for the study was collected in the summer period of 2005–2008 in Dalnezelenetskaya Bay of the Barents Sea. Symbiotic amphipods were collected from the carapace, limbs, abdomen, mouth� parts, and gills of red king crabs. Species identification and the amphipod measurements were performed in the laboratory. To clarify intraspecific relationships, we studied the distribution of amphipods of different sizes on differ� ent body areas of the crab. Localization of the individ� ual specimens of the red king crab and that of the entire population were studied (in the latter case, the data obtained for all crabs were pooled). In both cases, we determined the absolute number of symbionts and their proportion on a certain area of the host body. The symbionts were conventionally divided into two groups: “large” individuals, among which at least 90% were sexually mature crustaceans, and “small” ones, which were mostly juvenile specimens. The I. anguipes