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Oxygen production and comsumption rates were determined for the various communities (plankton, sediment, and seagrass-plus-epiphytes) associated with 2 adjacent seagrass communities, one dominated by Zostera marina and the other by Ruppia maritima. Annual estimates of gross production summed for all communities were high compared to other reports (ca 1600 gC m-' and 1100 gC m-* in the 2. marina and the R. maritima dominated communities, respectively). Plankton and sediment communities accounted for ca 45 and 36 % in the 2 areas, respectively. Seasonal patterns of production for the 2 areas differed. In the 2. marina area, plankton and sediment production dominated during summer, whereas in the R. maritima area production of seagrass (plus epiphytes) dominated throughout the study. Temporal trends for oxygen production and consumption of the plankton and sediment components corresponded closely and suggested direct in situ utilization. However, a lag observed between production and consumption in the seagrass-plus-epiphyte component indicated indirect utilization mediated by microbially dominated decomposition and remineralization processes.The ratio of annual gross production to dark respiration (P:R) exceeded 1.0 in both seagrass communities and for all components, suggesting net export and/or burial of carbon in these systems.

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