Effects of predation by fishes on the epifaunal community at Portsea, Victoria.

Exclusions were attached to artificial substrata to investigate the relative effects of predation on the development of epifaunal communities at Portsea. Exclusions were black plastic mesh cages enclosing panels that were attached to rigs under the Portsea Pier. Bare control panels and cage controls where included in the experimental design. Cage controls had the bottom and half of the roof on the cage removed. There were 2 replicate panels of each treatment that were immersed for 2, 4 or 7 months and there were 6 runs of the experiment from October 1975 to November 1977. At the conclusion of each run of the experiment the panels were fixed in 4% formalin-seawater solution. In the laboratory, the number of individuals and percent cover of colonial species on each panel were recorded.

Surveys identified that grazing fish were the most abundant predator of the epifaunal community at Portsea during the experiment. Predation significantly affected the pattern of establishment of the epifaunal community. There were fewer ascidian recruits and more diverse communities on bare control panels because fish predation prevented monopolisation of space by dominant ascidian competitors. On caged panels were there was no fish grazing, the survival of colonial ascidians was greater and the panels were dominated by arborescent bryozoans and ascidians.