Variability in biomass and primary productivity in an eelgrass (Zostera marina L.) community

Spatial variability of biomass and both spatial and temporal variability in primary productivity of eelgrass (Zostera marina L.) and its epiphytes were evaluated for an eelgrass community in Back Sound near Cape Lookout, North Carolina, during May and June, 1981. Five quadrats, each 4 m X 4 m, were marked on a transect parallel to the low tide water line on that portion of the eelgrass bed that was exposed at low spring tide. Above-ground biomass was sampled by clipping the eelgrass at the sediment surface in randomly selected 0.25 m² areas within each quadrat. Primary productivity was assessed by the ¹⁴C-CO₂ technique.

Analyses of variance and a posteriori multiple range tests showed that eelgrass biomass and primary productivity varied significantly through space (among quadrats). Temporal variance in eelgrass primary productivity was also shown to be significant. However, neither spatial nor temporal variability in primary productivity were detected for the epiphytes.

Any aquatic primary producer can be expected to vary its productivity with water depth, but spatial variability in primary productivity of aquatic macrophytes in other directions has not been assessed. The results of this study indicate the importance of evaluating spatial variability in primary productivity in any study of carbon dynamics in a seagrass community. Such spatial variability may also be important in other types of plant communities and deserves further examination.

That statistically significant (P < .05) spatial variability in primary productivity of epiphytes was not detected is evidence for considerable homogeneity within the epiphyte community. That temporal variability was not detected is surprising, and is possibly the result of the short period of field studies.