Abstract
Comparison of the amount and nature of suspended matenal within Pos~donia oceanica
canopies, in 6 meadows in the Spanish Mediterranean coast differing in extent and depth, with those
in the overlying waters showed the canopies to be significantly enriched in particulate organic carbon,
nitrogen and phosphorus relative to the overlying waters (on average, 87, 34 and 54 % more C, N and
P, respectively). Biovolume of detntus (both angiosperm-denved and plankton-denved) was large, par-
ticularly within seagrass canopies, where it dominated the seston pool (about 5-fold greater biovolume
than that of living particles), compared to a roughly equal biovolume of detntal and llving particles in
the parhcle pools in the overlying waters. The dominance of detrital particles was further reflected in
the high C/N and C/P ratios of the suspended materials (median atonuc C : N . P ratios = 492: 40.9: 1 and
596:45.1 of the matenals suspended within the canopy and in the overly~ng waters, respectively),
which were intermediate between those of living plankton and P oceanica. The relative ennchment of
P oceanica canopies by part~cles tended to be greatest when particle loads in the overlying waters
were small, suggesting that the effect of seagrasses as traps of particles is enhanced in particle-poor
waters The results obtained support the hypothesis that the water within seagrass canopies is enriched
by (mostly detrital) part~cles, particularly In particle-poor waters T h ~ s suggests that seagrasses not only
contribute a substanhal fraction of the particles themselves, but also act as sinks of particles. | This work is a contribution to the project
MAS3-CT96-0053 of the ELOISE programme, funded by MAST I11 (CE)