Posidonia oceanica ‘banquettes’: a preliminary assessment of the relevance for meadow carbon and nutrients budget

The massive supra-littoral deposit of leaf litter from the endemic Mediterranean seagrass Posidonia oceanica in Nueva Tabarca Island (Alicante, Spain), have been investigated to obtain a first assessment of its potential importance for the carbon and nutrients budget of the meadow. From approximately 18–500 kg of dry wt m 1 of shoreline P. oceanica leaves formed conspicuous wedgeshaped accumulations ( banquettes ) all along the bay, with heights ranging from 50 to 220 cm. The materials accumulated in the banquettes represented 50.7, 71.0, 27.2, and 8.7% of the annual biomass, carbon, nitrogen, and phosphorus production of the meadow, respectively. From the proposed accretion-erosion model of the banquette, it is concluded that the only true annual sink (loss) for the meadows, would be that represented by the material of the banquettes consumed by terrestrial detritivores and/or exported further away. The majority of the accumulated material would, therefore only constitute a temporary C, N, and P sink for P. oceanica meadows, of a constant average size.