Effects of macroalgal host identity and predation on an amphipod assemblage from a subtropical rocky shore

Abstract

Seaweeds play a key role in the rocky-shore fauna by providing shelter and food for many invertebrate species, which in turn compose the diet of benthic and pelagic predators. This study investigated the effect of the macroalgal host species on an assemblage of associated amphipods, and tested if the host mediates the vulnerability of amphipods to predation. The association of amphipods with the macroalgal hosts Dichotomaria marginata, Padina gymnospora, and Sargassum filipendula was evaluated seasonally for 1 year on a subtropical rocky shore on the southeastern coast of Brazil. The density of amphipods did not vary with season or host. However, the composition of amphipod species was sensitive to the host macroalgal species and varied temporally. A field experiment showed no clear effect of predation on the amphipod assemblage. Also, predation did not explain the spatial or temporal variation of the amphipod assemblage. Our results indicate that the identity of the macroalgal host drove the composition of the associated amphipods, while predation may have a minor role. Therefore, the loss of habitat-forming organisms such as seaweeds is expected to have drastic consequences for the composition of associated fauna, and consequently on the flow of matter and energy in coastal ecosystems.