Figure 4. Conceptual framework of the interaction between the amount of light, nutrient in- puts, and water residence time across different types of estuaries, based on geomorphology from carbonate reefs to river-dominated deltas. The horizontal arrows indicate an increase or decrease of sediment and nutrient inputs, wetland-to-estuary ratio, and benthic and pelagic productivity. The presence or absence of mangroves, sea grasses, and coral reefs in each coastal setting is indicated by the bars, as are the influences of fresh water and plankton productivity. Numbers representing study sites were placed along the bars depending on the dominant ecosystem found at each site: 1, Everglades, Florida; 2, Puerto Rico (wet); 3, Puerto Rico (dry); 4, San Juan, Venezuela; 5, Morrocoy National Park, Venezuela; 6, Los Roques, Venezuela; 7, Ciénaga Grande, Colombia; 8, Bocas del Toro, Panama; 9, Twin Cays, Belize; 10, northern Belize wetland complex; 11, Sian Ka’an, Mexico; 12, Celestun Lagoon, Mexico; 13, Terminos lagoon, Mexico. Modified from Downing and colleagues (1999).
Magdalena River, a large freshwater subsidy to the region.Arid regions of theYucatán Peninsula receive extensive groundwater flow in the Sian Ka’an and Celestun Lagoons (Herrera-Silveira and Comin 2000). More moist regions include the San Juan River estuary in Venezuela, Bocas del Toro in Panama, Terminos lagoon in Mexico, and the Everglades watershed in Florida (table 2). Puerto Rico is a high island with extreme differences in precipitation, representing arid and moist sites at similar geographical locations. Although the tidal regime across sites is small (0.2–0.5 m, except in San Juan River estuary; table 2), water residence time differs among the sites depending on the magnitude of river discharge, as in the
Ciénaga Grande de Santa Marta, Colombia (7–11 days), and Celestun Lagoon, Mexico (25 days). We define a fertility gradient across these geomorphological types as associated with nutrient input, residence time, and light regime.
The frequency and magnitude of disturbance, both natural and human, are also important considerations in the envi- ronmental signature of a coastal setting. Hurricanes have a strong effect on the ecological conditions of the Caribbean region. Although hurricane impacts are generally greater in oceanic (e.g., Puerto Rico, Twin Cays, Belize) than in conti- nental seascapes (e.g., San Juan,Venezuela; Sian Ka’an, Mex- ico; table 2), the latter can also receive considerable damage.
September 2004 / Vol. 54 No. 9 • BioScience 849