Epibiosis in a guild of sessile subtidal invertebrates in south-eastern Australia: a quantitative survey

Abstract

We report the first quantitative survey of the degree to which a guild of subtidal invertebrates was fouled by macro-organisms. Twenty common invertebrate species from five sites on the exposed rocky coast of south-eastern Australia were included in the survey. The survey focussed on representatives from four phyla, namely; ascidians (9), a bryozoan (1), coelenterates (2) and sponges (8). An indication of temporal variation in fouling was obtained by quantifying the number and cover of fouling organisms in autumn and spring. Considerable variation in fouling was apparent between species. Only 3 species (2 colonial ascidians and a coelenterate) competely lacked epibionts, while the highest cover of foulers was observed on solitary ascidians; in one instance the mean cover of epibionts exceeded 98% on Pyura spinifera. Significant temporal variation in the cover or number of fouling organisms was observed for 7 of the species examined. Significant increases in cover during the spring sampling period were attributable to a greater cover of non-calcareous algae, tube-dwelling spionid polychaetes or hydroids. The quantitative data presented here are in close agreement with published, qualitative data collected in Bermuda, but reveal some discrepancies with other qualitative data on fouling from the western Meditteranean.