Effects of epibiota on assemblages of fish associated with urban structures

The increasing number of artificial structures in shallow marine waters has provoked research on the ecological function of artificial habitats. The aim of the present study was to investigate interactions between fish and sessile biota growing on urban structures in coastal waterways. The biota growing on subtidal hard substrata is thought to have a large effect on the composition and distribution of associated fish. Hence, in Sydney Harbour, Australia, experiments were done to test interactions between fish and epibiota sampled on pilings at 4 marinas. The abundance and diversity of fish were strongly positively correlated with the amount of foliose algae, mussels and solitary ascidians on pilings. This correlative evidence was further investigated by experimental manipulations of the amount of conspicuous epibiota on pilings. Removal of these organisms showed a marked decrease in the numbers of many types of fish. Conversely, the addition of mussels to pilings increased the abundance and diversity of associated fish. The cover of complex epibiota on pilings at marinas may strongly affect the abundance of many species of fish and therefore influence the types of fish that recruit to these artificial habitats. Such knowledge on the ecological processes occurring in marinas is an important step in recognising the value of these artificial structures as habitat for marine organisms.