The cycling of dissolved organic matter (DOM) and its significance to ecosystem metabolism was studled over a 16 mo period in a Thalassia testudjnum dominated meadow. The benthos was usually net autotrophic (annual gross primary production to respiration ratio [P:R] = 1.3) while water column respiration (R) exceeded gross primary production (annual P:R = 0.3). Net fluxes of dissolved organic carbon (DOC) from the benthos primarily occurred in the light (0 to 18 mmol C m-2 d-1) and from seagrass-dominated areas, suggesting that release of DOC was mainly due to seagrass exudation. Net benthic DOC fluxes measured in the light were significantly correlated (p < 0.0001, n = 61) with 'benthic net primary production (NPP). Average daily benthic NPP was significantly correlated to water column R (p < 0.002, n = 7) and appeared to explain about 88% of the variability in daily water column R. Estimates of bacterioplankton growth efficiencies ranged from 21 to 38 %, with peaks corresponding to maximal benthic DOC fluxes in spring and summer. Bacterioplankton were responsible for the remineralization of most (>50%) of the DOC released from the benthos on a daily basis. Annual estimates of bacterioplankton C demand, based on water column R (~8 mol C m-2 yr-1), represented >50% of the benthic NPP (~14 mol C m m-2 yr-1). These measurements indicate a stronger linkage between benthic and water column processes than previously believed, and it appears that water column heterotrophic processes are largely dependent upon seagrass exudation.
Marine Ecology Progress Series, ed. Otto Kinne, Volume 180, 1999, pages 149-160.
© 1999 by Inter Research