The primary productivity of mangrove swamps, submerged seagrass beds, phytoplankton, and benthic microalgae was measured in the Laguna de Terminos during 1978-1981. Riverine input affected mangrove productivity and chlorophyll levels. Banded trees at the riverine site showed a more rapid rate of growth than the trees at the higher salinity site. Litter bag decomposition measurements of mangrove leaves were also higher at the riverine site, with 24% remaining after 6 months as compared to 50% at the high salinity site. Chlorophyll a concentrations ranged from 0.3-8.2 mg/m super(3). There was a seasonal pattern in Chl a) concentration with the lowest mean values ( similar to 1 mg/m super(3)) during the dry season (Feb.-June) and the highest mean values ( similar to 5 mg/m super(3)) during and following the rainy season.