Motile macroinvertebrate assemblages associated with submerged Posidonia oceanica litter accumulations

Abstract

In the Mediterranean, seagrass leaf litter derived from Posidonia oceanica beds constitutes an important source of detritus. Large areas with P. oceanica leaf litter are ubiquitous in the infralittoral, but data on the species assemblages characterising this habitat are lacking. Samples of leaf litter were collected in December 2001 from 8 stations in each of two bays on the northern coast of Malta, using a suction sampler. A total of 4794 motile macroinvertebrates comprising 43 species were recorded. Overall, diversity and evenness values were low, however, abundance values were very high. Detritivorous crustaceans were the most abundant taxon (>97 %), with amphipods having the highest abundance (81.8 %). Our results indicate that P. oceanica leaf litter is a distinct habitat that supports characteristic motile macroinvertebrate assemblages dominated by gammarid amphipods. Mediterranean marine Gammarus spp. are typically found in brackish habitats, and only infrequently occur in fully marine waters. However, no sources of brackish water were present in the vicinity of our study sites, which seems to indicate that the occurrence of Gammarus spp. in P. oceanica leaf litter accumulations may be widespread. We suggest that the P. oceanica leaf litter habitat supports unique macroinvertebrate assemblages composed mostly of motile detritivores and which may constitute an important link in transferring production from P. oceanica leaves to higher trophic levels.