Land use, water quality, and the history of coral assemblages at Bocas del Toro, Panamá

As human activities have intensified along tropical coastlines, the anthropic influence on adjacent coral reefs has become increasingly deleterious. Changes in land use generally degrade water quality, but controversy persists over the degree to which reduced water quality affects the ecology of reef communities. We cored reef frameworks at 4 sites in Baha Almirante, a semi-enclosed, coastal lagoon in northwestern Panam, to explore the historical relationship between turnover in coral-species dominance and terrigenous input. The coral constituents of the cores were analyzed in tandem with lignin-phenol concentrations. Chronologies and sedimentation rates were determined from 210 Pb profiles in the cores. Increased terrigenous input from agricultural development and expansion of the human population degraded water quality in Baha Almirante over the last century. Documented episodes of heavy rainfall after 1970 accelerated a phase shift from dominance by branching corals of the genus Porites to dominance by the lettuce coral Agaricia tenuifolia at water depths of 5 to 10 m by increasing runoff, increasing sediment and nutrient loads, and lowering light levels. The phase shift in coral dominance was unprecedented on a millennial time scale and the degree to which it occurred varied along a gradient of terrigenous input to the Baha.