Effect of temporal variation and size of herbivorous amphipods on consumption levels of Sargassum filipendula (Phaeophyta, Fucales) and their main epiphyte, Hypnea musciformis

Abstract

The impact of herbivorous amphipods on a community of macroalgae does not depend only on the species present. Two equally important factors are the relative abundance and potential consumption of herbivorous species. The aim of this study was to determine the role of temporal and size variation of herbivorous amphipods in the consumption of Sargassum filipendula and their main algal epiphyte Hypnea musciformis. Monthly collections of 15 fronds of S. filipendula were carried out between June 2000 and May 2001 at Fortaleza beach, north coast of the state of Sao Paulo, Brazil, to evaluate the size structure of the herbivorous amphipods of the families Hyalidae and Ampithoidae and the occurrence of epiphytic algae associated with S. filipendula. Ampithoidae and Hyalidae amphipods were identified, separated in size classes and counted. Choice consumption assays were performed to estimate the grazing rates of amphipods of different size classes on S. filipendula and Hypnea musciformis. The amphipods showed temporal variation in abundance and recruitment in all sampling periods. Algal consumption varied among species and size of amphipods with a tendency for increased consumption with size (from a mean daily value of 0.143 g/frond for 0.75 mm Hyale nigra to 6.757 g/frond for 4.0 mm Cymadusa filosa). Consequently, the contributions of each species for the removal of the algae were different along the year. Our results indicate that amphipod algal herbivory should be evaluated at fine taxonomic resolution considering the individual contribution of different size classes