Depth and Seasonal Distribution of Some Groups of the Vagile Fauna of thePosidonia oceanicaLeaf Stratum: Structural and Trophic Analyses

Abstract

Abstract.The taxonomical and trophic structures of the vagile fauna communities of the leaf stratum in aPosidonia oceanicameadow at Ischia (Gulf of Naples, Italy) were investigated at five stations along a depth gradient (1 to 25 m). Sampling was performed in July, November, February, and May. The analyzed groups ‐ polychaetes, molluscs, tanaids, isopods, amphipods, and decapods ‐ exhibited similar distributional trends in all seasons, with coenotic discontinuities occurring at well‐defined depths. The same zonation pattern was produced by feeding‐guild analysis. Eleven trophic groups were identified. The most abundant groups were: Herbivores, which were found mainly at the shallow stations; Herbivores‐deposit feeders, which were widely distributed along the transect; Deposit feeders‐carnivores, found mainly at the deep stations.This study suggests that in thePosidonialeaf stratum, herbivores and herbivores‐deposit feeders, as consumers of epiphytic micro‐ and macroflora and deposited particulate organic matter, play an important role in the energy transfer from producers to higher trophic levels of the system.