The basic ecology of seagrass beds was investigated by comparing biomass, productivity and density of Thalassia testudinum (turtle grass) at three sites: Puerto Vargas, Punta Cahuita and Río Perezoso, in Cahuita National Park, Limón, Costa Rica, over a two month period (March-April 1999). Above ground biomass, density, and productivity were highest in the Puerto Vargas site while Punta Cahuita had the least non-green above ground biomass was significantly lower in total biomass than Puerto Vargas. Punta Cahuita was distinguished by the largest grain size, a very hard substrate, and shallower water. Río Perezoso, on the other hand, had extremely fine sediment and lower salinity, while Puerto Vargas was intermediate both in sediment size and environmental conditions. It appears, therefore, that higher biomass and productivity result from a combination of moderate environmental characteristics and an intermediate sediment size.
Keywords: Seagrass, Thalassia, Cahuita, Costa Rica, reef lagoon, productivity, biomass