Coastal lagoons of Mexico : their origin and classification

The coastal zone of Mexico extends 10,000 kilometers along the borders of the Pacific, Gulf of Califorrúa, Gulf of Mexico and Caribbean and contains approximately 125 coastal lagoons defmed here as: "a coastal zone depression below MHHW, having permanent or ephemeral communication with the sea, but protected from the sea by sorne type of barrier." Mexican coastal lagoons vary widely in their physical and environmental characteristics and in their degree of man's use and modification. They are geologically classified according to origin of the depression and barrier characteristics as: l. Differential Erosion (usually drowned valleys but includes solution depressions); 11. Differential Terrigenous Sedimentation (typically associated with fluvial¡ deltaic systems); III. Barred Inner Shelf (offshore barrier on inner continental shelf); IV. Organic (usually coralgal but incIudes also mangrove and other organisms); V. Tectonic-Volcanic (directIy linked with faulting, folding, or voleanism). Many coastal lagoons are compounds of two or more basic classes. Interrelating the original geomorphic characteristics with geologic development history, coastal oceanography and regional climatology, one may predict major types of eXisting lagoon environmental systems. Brief case studies illustrate the main meXican coastallagoon types.