Susceptibility to sea-level rise
Medium Medium High Low High
High Medium Medium High High
Low High Medium
Medium High Medium Low Low
Low Low Low Medium Medium
Low Medium Low
Mean tidal range
0.5 0.5 0.5 3 0.5
0.5 0.5 0.25 0.25 –
0.5 0.5 0.5
Precipitation-to- evapotranspiration ratio
Medium Medium Low High Medium
Low Low High Low Medium
Low Medium Medium
Type of landscape
Continental Oceanic Oceanic Continental Continental
Oceanic Continental Continental Oceanic Continental
Continental Continental Continental
Karstic Nonkarstic Nonkarstic Nonkarstic Karstic
Karstic Nonkarstic Nonkarstic Karstic Karstic
Karstic Karstic Nonkarstic
Low Medium Low High Low
Low High Low Low Low
Medium Low High
Table 2. Characteristics of the study sites.
Low High High Medium Low
Low High High Low Low
Low Low Low
Low to medium Medium (river) Low High (river) Low
Low High (river) Low Low Low to medium
High to medium Medium to high Medium to high
Everglades, Florida Puerto Rico/wet Puerto Rico/dry San Juan, Venezuela Morrocoy National Park, Venezuela Los Roques, Venezuela Ciénaga Grande, Colombia Bocas del Toro, Panama Twin Cays, Belize Northern Belize wetland complex Sian Ka’an, Mexico Celestun Lagoon, Mexico Terminos lagoon
848 BioScience • September 2004 / Vol. 54 No. 9
a. Volcanic activity.
The coastal seascape can be described by the ratio of emer- gent to submerged area (wetland-to-water ratio). The relative distribution of reef–sea-grass–wetland ecosystems across a coastal seascape varies with the four geomorphological types used in this classification of coastal settings, which can be linked to specific combinations of geophysical energies. Reefs and lagoons are marine-dominated coastal settings, with coral reef and sea grass communities dominating the coastal seascape. In these coastal settings, the emergent zone is lim- ited to the intertidal area, with a reduced wetland-to-water ra- tio. Light is plentiful in the submerged zone of this coastal setting, yet nutrients are low, resulting in oligotrophic con- ditions. In river-dominated coastal settings, coral reefs and sea grasses are less abundant in the submerged zone, and wetlands dominate the more extensive emergent zone. Depending on the degree of freshwater input and tidal range, the ratio of emergent to submerged zone increases in these coastal settings, as in a delta, for example.
Many of the sites we reviewed have more than one geo- morphological type, with multiple gradients resulting in di- verse combinations of coastal ecosystems (figure 4). For example, Terminos lagoon, in Mexico, is a delta-lagoon com- plex that has extensive marshes and mangroves in its river- dominated seascapes, in contrast with the extensive sea grasses in its marine-dominated regions. The environmental signa- ture concept describes how each of these ecosystems in a coastal seascape has a characteristic structure and function that can be related to available resources (e.g., nutrients), regula- tors (e.g., salinity), and hydrologic gradients unique to a coastal setting.
Environmental signature of selected coastal settings The environmental signature of a coastal (regional) setting is a combination of geomorphological type, geophysical ener- gies, and levels of disturbance. There are conspicuous differ- ences in topographic relief throughout the entire Caribbean region.Areas with average altitudes from 2000 to 3000 m above mean sea level (msl), associated with volcanic activity, can be found in Honduras, El Salvador, Costa Rica, Panama (e.g., Bocas del Toro; table 2), and the Lesser Antilles. The highest altitude adjacent to the coastal zone in the Caribbean, located in the Ciénaga Grande de Santa Marta deltaic region of Colombia, is 5775 m above msl. In contrast, lower altitudes (less than 500 m above msl) are geologically associated with extensive karstic topography, as in the Yucatán Peninsula (Celestun, Sian Ka’an), Belize (Twin Cays), and south Florida (the Everglades; table 2). Topographic relief classes were assigned to each site: low (e.g., the Everglades), medium (e.g., San Juan River), or high (e.g., Ciénaga Grande), depending on the major regional geological features. Four of the 13 sites are oceanic islands; two sites are on high islands and two on low islands.
The combination of regional climate and topographic features influences the amount of freshwater input at each site. Although the Caribbean coast of Colombia is arid, the Ciénaga Grande has a deltaic geomorphology because of the