Weak Effects of Epibiota on the Abundances of Fishes Associated with Pier Pilings in Sydney Harbour

Biogenic habitats have profound effects on the distribution and abundances of many organisms. Epibiota are major biogenic components of hard substrata in marine habitats, particularly on artificial structures such as pier pilings, and have the potential to influence organisms associated with these structures. This study tested hypotheses about effects of epibiota on abundances of fishes associated with pilings in Middle Harbour, Sydney. Amount of epibiota had no effect on abundances of most species of fish, suggesting that epibiota are not important resources for these species. Abundances of the hulafish, Trachinops taeniatus, were, however, found to be greater around pilings with large than pilings with small amounts of epibiota at one site, at each of two times. Experimental removals of epibiota from pilings were done to test the hypothesis that epibiota are an important resource to T. taeniatus. Despite great temporal fluctuations in abundances over the duration of the experiment, the response of T. taeniatus to the removal of epibiota from pilings was as predicted, falling to zero following removal of epibiota. Although this suggests that epibiota are an important resource for this species, this pattern was spatially and temporally variable. We suggest that variation in the amount of epibiota has minor effects on the abundances of fishes around pilings.