Abundance of mobile epifauna: The role of habitat complexity and predation by fishes

Abstract

Variation in the abundances of epifaunal organisms living on the large brown alga Sargassum was quantified for 13 months. For most taxa, abundances of epifauna were greatest during the austral winter (July to September). Abundances of epifauna showed a negative correlation with Sargassum biomass but a positive correlation with levels of epiphytes. Two hypotheses were tested to elucidate the causes of these temporal variations: (1) abundance of epifauna was constrained by habitat complexity (as defined by levels of epiphytic algae not Sargassum biomass); (2) predation by fishes maintained epifaunal abundance below the carrying capacity of the environment. The first hypothesis was tested using artificial macroalgal mimics with different levels of epiphytes. Multivariate analysis of a number of epifaunal taxa revealed significant effects of levels of epiphytes: abundances of most taxa were greater on epiphytised mimics and community composition was different between treatments. The second hypothesis was tested using a caging experiment to exclude fishes and the results showed no demonstrable effects of predation. However, significant caging artifacts were found which could have masked effects of predation. It is suggested that the additional complexity of habitats provided by epiphytes has an important effect in determining seasonal patterns of abundance of epifauna.