Effects of fish predation on Posidonia oceanica amphipod assemblages

Abstract

Amphipod assemblages that inhabit Posidonia oceanica seagrass meadows are potentially relevant trophic resources for ichthyofauna. However, the effects of fish predation on amphipod assemblages in this system have received little attention. To address this gap in knowledge, experimental manipulations of predation intensity (exclu- sion and inclusion cages) were conducted at two sites in a Mediterranean marine protected area, where different lev- els of fish predation were expected to occur. We found that in the absence of predatory fishes (exclusion cages), total amphipod density and biomass were higher than in uncaged areas and partially controlled cages. At the species level, Caprella acanthifera and Iphimedia minuta responded to caging with increased abundance, while in most cases dif- ferent species did not exhibit differences in density or bio- mass between treatments. The presence of one enclosed labrid fish predator (inclusion cages) resulted in a lower density and biomass of Aora spinicornis and a lower bio- mass of Phtisica marina, although total amphipod density