MEPS 155:29-44 (1997)  -  doi:10.3354/meps155029

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

Cebrián J, Duarte CM, Marbà N, Enríquez S

We examined the seasonality and magnitude of the leaf-blade, rhizome and root biomass and production, along with the fate of leaf-blade production, of the 4 Mediterranean seagrass species Posidoniaoceanica, Cymodoceanodosa, Zosteranoltii and Zosteramarina in a protected northern Spanish bay (Cala Jonquet, 42° 18.26' N, 3° 18.11' E) to estimate (1) the annual production consumed by herbivores or decomposed 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 agreement with past studies), except for that of Z.noltii, which suggested a rapid loss of its production either to herbivores or as detritus. Z.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 Z.noltii. Most of the production of the 4 species was decomposed by detritivores, which supports the importance of the detritivore food-web in the use and recycling of seagrass production. Consumption of seagrass leaf production by herbivores appeared to be higher for C.nodosa and Z.noltii, the species with the greatest leaf turnover rates, than for Z.marina and P.oceanica. Total heterotrophic use of seagrass production (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 productive species (C.nodosa and Z.noltii) and represented a larger percentage of the production of the former species (9.2 and 16.8% respectively) compared with the latter species (about 1.5%). That suggests that Z.marina and P.oceanica may accumulate larger pools of refractory detritus and that their production is recycled more slowly than that of C.nodosa and Z.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 leaf turnover 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.

Mediterranean seagrasses · Fate of production · Herbivory · Decomposition · Production excess

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