Cuba, Mollusks, 210Pb dating, Dead shells, Sagua La Grande river, Sedimentation, Mercury - analysis, Environmental Monitoring - methods, Estuaries, Mollusca - growth & development, Biodiversity, Water Pollutants, Chemical - analysis, Eutrophication, Mercury - toxicity, Animals, Water Pollutants, Chemical - toxicity, Tropical Climate, Geologic Sediments - che...