Shells of Patella aspera as 'islands' for epibionts

In this study we examined the epibiont assemblage on shells of the living limpet Patella aspera. Limpets were collected at two sites at each of the nine islands of the Azores, totalling 707 individuals examined. Shells were measured and all the epibiota identified to the lowest taxonomic resolution possible. 190 taxa were recorded, of which 97% were algae, including 17 new records for the Azores. Only five shells were devoid of fouling organisms. The assemblage was dominated by a few algal taxa, whereas the majority of species occurred on less than 10% of the shells. A significant and positive relationship was generally found between basibiont size (shell length) and epibiota richness. The strength (slope) of the relationship, however, varied between islands and sites. These results suggest that a range of processes operating at multiple spatial scales influenced epibiont assemblages. Many features identified in these assemblages resemble, in many ways, those examined in island biogeography, suggesting that basibionts may be considered as 'islands' and may provide a suitable model system to test ecological hypotheses about ecosystems that are not so amenable to experimentation.