EPIBIOTIC COMMUNITIES ON SUBLITTORAL MACROINVERTEBRATES AT SIGNY ISLAND, ANTARCTICA

The epibiotic communities on locally abundant macroinvertebrates, in p articular the brachiopod Liothyrella uva and the limpet Nacella concin na, were examined from depths between 0 and 50 m at Signy Island, Anta rctica. The percentage cover by epibionts on Liothyrella increased fro m <20% on the smallest individuals to >50% on the largest, and decreas ed slightly with depth. The percentage cover of Nacella by epibionts i ncreased with size of individual over an approximately similar range o f values, but in contrast with Liothyrella increased greatly with dept h. Cheilostome bryozoans and annelids of the genus Spirorbis formed >9 0% (by area) of the colonists on Liothyrella and 30-60% on Nacella, th e coralline alga Lithothamnion and sponges making up the remainder. Th e bryozoans, which generally dominated the epibiotic communities, comp rised complex associations of species which could be described as eith er generalists, host-specific epibiotic, low specificity epibiotic or locally abundant background species. Positive associations of both occ urrence and abundance were found between some of the bryozoans living epibiotically on the brachiopod Liothyrella. The overgrowth interactio ns recorded, between the three main epibiotic faunal taxa; sponges, br yozoans and annelids, were essentially hierarchical. Sponges usually o vergrew Bryozoa, and Bryozoa overgrew Spirorbis as well as occasionall y smothering small brachiopods. In four adult Liothyrella death may ha ve been caused by the epibiotic bryozoan Arachnopusia inchoata growing over the gape, so preventing feeding and/or respiration.