The in situ production of methane was monitored in several types of tropical benthic communities. A bed of Thalassia testudinum located in Caesar Creek (Florida Keys) exhibited the highest methanogenic activity (initial rates = 1.81 to 1.86 μmol CH₄/m² per h) as compared with another seagrass (Syringodium sp., 0.15 to 0.33 μmol/m² per h) and two coral reef environments (Hydro-Lab, 0.016 to 0.10 μmol/m² per h; Curaçao, 0.14 to 0.47 μmol/m² per h). The results suggest that a wide variety of benthic metabolic processes (e.g., photosynthetic oxygen production) influences methane production rates.