Posidonia oceanica habitat loss and changes in litter-associated biodiversity organization: A stable isotope-based preliminary study

1.Posidonia oceanica (L.) Delile meadows are experiencing severe decline, with significant effects on P. oceanica meadow biodiversity, food webs and associated ecological processes. Despite the importance of this habitat, very little information with which to comprehend and predict the effects of habitat loss on the trophic traits of meadow-dwelling species is available.2.The study addressed the effect of changes in P. oceanica cover on the trophic niche of macroinvertebrate litter-associated species and on their consumption of various basal resources along the upper limit of a P. oceanica meadow in the central Tyrrhenian Sea.3.Census data and C and N stable isotope analysis were used to characterize changes in the trophic niche of species and the contribution of basal resources to food webs along a meadow coverage gradient.4.Falling P. oceanica cover was associated with lower species richness and animal density. In the low-coverage area of the meadow, the organic matter content of basal resources decreased, and the trophic generalism of species increased while their trophic niche overlap declined. In addition, consumption of living P. oceanica plants and epiphytes decreased, and consumption of sediment-derived organic matter increased.5.The results suggest that the community associated with P. oceanica litter is particularly sensitive to meadow degradation, which affects trophic structuring and nutrient pathways within the food web.