Food sources of two detritivore amphipods associated with the seagrass Posidonia oceanica leaf litter

Abstract

This study focused on the ingestion and assimilation of Posidonia oceanica (L.) Delile litter by Gammarella fucicola Leach and Gammarus aequicauda Martynov, two dominant detritivore amphipods of the P. oceanica leaf litter. Scanning electron microscope observations indicated that leaf litter is highly colonized by diverse diatoms, bacteria and fungi, which may constitute a potential food source for the litter fauna. Gut content observations demonstrated that these species eat P. oceanica litter, and that this item is an important part of their ingested diet. Stable isotope analyses showed that the species do not experience the same gains from the ingested Posidonia. Gammarella fucicola displayed isotopic values, suggesting a major contribution of algal material (micro- and macro-epiphytes or drift macro-algae). On the other hand, the observed isotopic values of G. aequicauda indicated a more important contribution of P. oceanica carbon. The mixing model used agreed with this view, with a mean contribution of P. oceanica to approximately 50% (range 40–55%) of the assimilated biomass of G. aequicauda. This demonstrated that the two species, suspected to be detritus feeders, display in reality relatively different diets, showing that a certain degree of trophic diversity may exist among the detritivore community of the seagrass litter.

Keywords:

• Mediterranean Sea
• mixing model
• phytodetritus
• seagrass
• stable isotopes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Acknowledgments

This paper is dedicated to our colleague, Dr Michel Frankignoulle, who died in March 2005. We are very grateful to the staff of the oceanographic station STARESO for their welcome and assistance during field work. The comments and suggestions from anonymous referees greatly improved the quality of a previous version of the manuscript. We also thank the anonymous colleagues who have improved the present version of this paper. GL is a post-doctoral researcher of the Belgian National Fund for Scientific Research (FNRS). This study was supported by a FNRS contract (FRFC 2.45.69.03) and is MARE publication number 93.

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark