EPIBIOTIC COMMUNITIES ON SUBLITTORAL MACROINVERTEBRATES AT SIGNY ISLAND, ANTARCTICA

The epibiotic communities on locally abundant macroinvertebrates, in particular the brachiopod Liothyrella uva and the limpet Nacella concinna, were examined from depths between 0 and 50 m at Signy Island, Antarctica. The percentage cover by epibionts on Liothyrella increased from <20% on the smallest individuals to >50% on the largest, and decreased slightly with depth. The percentage cover of Nacella by epibionts increased with size of individual over an approximately similar range of values, but in contrast with Liothyrella increased greatly with depth. Cheilostome bryozoans and annelids of the genus Spirorbis formed >90% (by area) of the colonists on Liothyrella and 30-60% on Nacella, the coralline alga Lithothamnion and sponges making up the remainder. The bryozoans, which generally dominated the epibiotic communities, comprised complex associations of species which could be described as either generalists, host-specific epibiotic, low specificity epibiotic or locally abundant background species. Positive associations of both occurrence and abundance were found between some of the bryozoans living epibiotically on the brachiopod Liothyrella. The overgrowth interactions recorded, between the three main epibiotic faunal taxa; sponges, bryozoans and annelids, were essentially hierarchical. Sponges usually overgrew Bryozoa, and Bryozoa overgrew Spirorbis as well as occasionally smothering small brachiopods. In four adult Liothyrella death may have been caused by the epibiotic bryozoan Arachnopusia inchoata growing over the gape, so preventing feeding and/or respiration.