Habitat characterization of Posidonia oceanica leaf litter Stocks

Abstract

Decaying leaf litter originating mainly from unconsumed primary production from the seagrass Posidonia oceanica occurs in many places around the Maltese Islands, especially on the sandy bottoms of bays. The main objective of this work was to characterize the macrobenthic assemblages living in the leaf litter itself and to determine if there is any spatial variation in these assemblages between and within the bays studied. Samples were collected in December 2001, using a suction sampler. Spatial variation in the distribution of the litter macrofauna was analysed by using a nested hierarchical sampling design. A total of 25,481 live individuals comprising 95 species, and representing seven major taxonomic groups, were identified. The leaf litter habitat is dominated by detritivorous crustaceans (>97 %) of which amphipods (78.5 %) were the most abundant taxon. Although there was a large number of species the habitat was dominated by seven taxa, which accounted for 96.4 % of the total abundance. Species of the amphipod genus Gammarus (totalling 15,069 individuals) accounted for more than 59 % of the total abundance and dominated the habitat. There was no spatial variation at the level of bays and sides of the bays. Spatial variation was only detected up to 50m for the most common single species and up to 25m for the most common groups. The benthic assemblages of the leaf litter habitat are of considerable interest as the most common species are prey items for a variety of fish and thus important in transferring the production locked up in the relatively indigestible P. oceanica leaves to higher trophic levels. The crustacean detritivores are also important in increasing the rate of decomposition process and the metabolic activity of the system as a whole, as well as increasing the marine biodiversity of Maltese coastal waters.