MEPS 224:231-250 (2001)  -  doi:10.3354/meps224231

ABSTRACT: The effects of predation by fishes, in relation to habitat complexity and periodicity of sampling, on abundances of fishes and macroinvertebrates were investigated using controlled caging experiments during summer 1999/2000 at multiple locations (Blairgowrie, Grand Scenic, and Kilgour) in Port Phillip Bay, Australia. A second experiment evaluated biological and physical cage effects. Sites and habitats, but not caging treatments, could generally be differentiated by the assemblage structure of fishes. Regardless of species, small fishes were generally more abundant in seagrass than unvegetated sand, although the nature of this pattern was site- and time-specific. Depending on the site, abundances of fishes varied between cage treatments in ways that were consistent with neither cage nor predation effects (Grand Scenic), strong cage effects (Kilgour) or strong predation or cage effects (Blairgowrie). The abundance of syngnathids varied inconsistently between caging treatments and habitats within sites through time. Although they were generally more abundant in seagrass, whether or not predation or cage effects were observed depended strongly on the time of sampling. Atherinids and clupeids generally occurred more commonly over seagrass. In this habitat, atherinids varied between cage treatments in a manner consistent with strong cage effects, while clupeids varied amongst predator treatments in a way that could be explained either by cage or predation effects. Macroinvertebrates were closely associated with seagrass, palaemonid shrimps varied little with cage structure, and abundance of cephalopods appeared to be influenced by predation. Neither environmental (particle size and organic content) nor biological (abundances of meiofaunal crustaceans) attributes appeared to be altered by cage structure, but the statistical power of these experiments was sometimes low. Patterns in the abundances of fishes and macroinvertebrates are discussed in relation to predation and cage effects, habitat type, and the time of and location within which experiments were conducted.

KEY WORDS: Predation · Exclusion cages · Cage artefacts · Cephalopods · Crustaceans · Fish · Meiofauna · Seagrass · Unvegetated sand · Australia · Temperate