MAGNITUDE AND FATE OF THE PRODUCTION OF 4 COOCCURRING WESTERN MEDITERRANEAN SEAGRASS SPECIES

We examined the seasonality and magnitude of the leaf-blade, rhizome a nd root biomass and production, along with the fate of leaf-blade prod uction, of the 4 Mediterranean seagrass species Posidonia oceanica, Cy modocea nodosa, Zostera noltii and Zostera marina in a protected north ern Spanish bay (Cala Jonquet, 42 degrees 18.26' N, 3 degrees 18.11' E ) to estimate (1) the annual production consumed by herbivores or deco mposed by detritivores and (2) the production in excess of consumption and first-year decomposition, which should be an upper limit of long- term burial of refractory detritus. The leaf, rhizome and root biomass of the 4 species displayed a clear seasonal pattern (which is in agre ement with past studies), except for that of Z. noltii, which suggeste d a rapid loss of its production either to herbivores or as detritus. Z. marina and P. oceanica were the most productive species, and transf erred to consumers (herbivores and detritivores) about twice the produ ction transferred by C. nodosa and Z. noltii. Most of the production o f the 4 species was decomposed by detritivores, which supports the imp ortance of the detritivore food-web in the use and recycling of seagra ss production. Consumption of seagrass leaf production by herbivores a ppeared to be higher for C. nodosa and Z. noltii, the species with the greatest leaf turnover rates, than for Z. marina and P. oceanica. Tot al heterotrophic use oi seagrass production (consumption by herbivores and decomposition by detritivores) accounted for more than 80% of sea grass production in the 4 species. Yet, the excess of production not c onsumed nor decomposed during the first year ranged over 1 order of ma gnitude from the most (Z. marina and P. oceanica) to the least product ive species (C. nodosa and Z. noltii) and represented a larger percent age of the production of the former species (9.2 and 16.8% respectivel y) compared with the latter species (about 1.5%). That suggests that Z . marina and P. oceanica may accumulate larger pools of refractory det ritus and that their production is recycled more slowly than that of C . nodosa and Z. noltii. These results show marked differences in the f ate of production among the 4 Western Mediterranean seagrass species g rowing in Cala Jonquet and suggest that differences in the leaf turnov er rate could contribute to the explanation of differences in the fate of seagrass production, the species with faster-growing leaves losing a higher percentage of production to herbivores and recycling most of the residual detrital production, therefore storing relatively small pools of refractory detritus.