Magnitude and fate of the production of four co-occurring Western Mediterranean seagrass species

LVe examined the seasona1it)r and magnitude of the leaf-blade, rh~zome and root biomass and production, along with the fate of leaf-blade production, of the 4 Mediterranean seagrass species Posjdon~a oc.eanlca.Cymodocea nodosa, Zostera noltii and Zostera marina in a protected northern Spanish bay (Cala Jonquet, 42' 18.26' N, 3" 18.11' E) to estimate (1) the annual production consumed by herb~vores or decomposed by detritivores and (2) the production In excess of consumption and firstyear decomposition, which should be dn upper limit of long-term burlal of refractory detritus.The leaf, rhizome and root biomass of the 4 species displayed a clear seasonal pattern (which IS in agreement with past studies), except for that of 2. nolt~i, whlch suggested a r a p ~d loss of its productlon either to herbivores or as detritus.2. marina and P. oceanica were the most productive species, and transferred to consumers (herbivores and detritivores] about twice the production transferred by C. nodosa and 2. noltii.Most of the production of the 4 species was decomposed by detritivores, whlch supports the importance of the detritivore food-web in the use and recycling of seagrass production.Consumption of seagrass leaf productlon by herbivores appeared to be higher for C. nodosa and 2. noltji, the species with the greatest leaf turnover rates, than for Z. marina and P. oceanica.Total heterotrophic use of seagrass product~on (consumption by herbivores and decomposition by detritivores) accounted for more than 80% of seagrass production in the 4 species.Yet, the excess of production not consumed nor decomposed during the first year ranged over 1 order of magnitude from the most (Z.marina and P. oceanica) to the least product~ve species (C.nodosa and 2. noltii) and represented a larger percentage of the production of the former species (9.2 and 16.8% respectively) compared ~vith the latter species (about I S ' % , ) .That suggests that 2. marinaand P. oceanica may accumulate larger pools of refractory detritus and that their production is recycled more slowly than that of C. nodosa and 2. noltii.These results show marked differences in the fate of production among the 4 Western Mediterranean seagrass species growing in Cala Jonquet and suggest that differences in the 1.eaf turnover rate could contribute to the explanation of differences in the fate of seagrass product~on, the species with fastergrowing leaves losing a higher perccntage of production to herbivores and recycling most of the residual detntal productlon, therefore stonng relatively small pools of refractory detritus.