Predatory fish do not always affect the early development of epibiotic assemblages

Foraging by predatory fish is thought to be one of the primary ecological processes affecting the abundances of plants and animals in subtidal habitats. The importance of this process was assessed on the subtidal surfaces of urban structures (pontoons and pilings) that represent major coastal habitats for marine organisms. Fish feed with greater intensity on epibiota attached to pilings than pontoons and it was hypothesised that greater predation on pilings explained why the structure of epibiotic assemblages differs between these habitats. I predicted that the structure of epibiotic assemblages would develop differently between pilings and pontoons in the presence of fish (plates open to predation) but not in the absence of fish (plates inside exclusion cages). Results revealed large differences in abundance between pilings and pontoons that were largely independent of the caged and uncaged plates. Predation may be intense (as it appeared on pilings) but unimportant because it does not explain observed abundances of prey (epibiota between pilings and pontoons).