Predation by fish on assemblages of intertidal epibiota: effects of predator size and patch size

We tested the hypothesis that effects of predation by fish on epibiota are independent of the size of fish and the area foraged. We used cages with different sizes of mesh to exclude fish of different sizes. Sizes of mesh were chosen following observations that there were small (<200 mm TL) and large (>200 mm TL) predatory fish at the study site. Predation by fish was intense on oysters and directly or indirectly reduced the density of the gastropod, Bembicium auratum. The cover of algae was positively affected by predation, possibly because predation on oysters created more space for algae. Predation by small fish (toadfish) was intense, but the effects of large fish were negligible. Predation was, however, independent of the sizes of experimental panels (i.e. area foraged) over the range examined (5×5, 10×10, 20×20 cm). Our results highlight the importance of doing experiments to test hypotheses derived from known aspects of the biology of the predators and prey being studied.