OF THE GULF OF MEXICO : CHARACTERIZATION AND DIAGNOSIS

INTRODUCTION The Gulf of Mexico is a tropical to subtropical sea, partly oligotrophic and with relatively restricted marine circulation given that it is an interior sea. The ocean dynamic is determined mainly by the Loop Current, which also has an influence on coastal water movement, particularly when eddies that separate from that current contribute to forming other currents close to the coasts. The force of the wind on the surface of the water plays an important role in coastal and ocean water dynamics. In contrast to what happens in most of the Caribbean, there are two different tidal systems in the Gulf per year, one is generated by trade winds during most of the year and the other is generated by the north winds, during the winter season. The Gulf is also characterized by the influence of great riverine systems (from Laguna de Términos to the Mississippi River Delta and the continental shelf of Florida), that create unfavorable environmental conditions for the coral reef biota. Yet even in the northeastern part of the Yucatan continental shelf, where there are no rivers, the effect of upwelling in the Yucatan Channel and perhaps also freshwater inflow from groundwater, also result in an unfavorable environment for forming coral reefs. Thus, on a large part of the Gulf of Mexico continental shelf, conditions for the development of coral reefs are not appropriate; in fact, of the approximately 360,000 km of shallow waters (less than 50 m deep) of the Gulf continental shelf, less than 1% is covered by emergent coral reefs, although the area colonized by coral biota is considerably larger. This study focuses on emergent and quasi-emergent coral reefs because they have been able to maintain sustained growth during the rise in sea level, during the Holocene transgression. This type of reef can only be found on the Mexican continental shelf inside the Gulf of Mexico and in shallow areas associated with the Florida Straits, as in the Florida Keys and the reefs to the northwest of Cuba. However, the latter are not included in this paper because their development and condition are determined by very different environmental circumstances to those in the Gulf, given that in the Florida Straits there are intense oceanic dynamics as a result of the constant flow of the Yucatan Current towards the Atlantic Ocean. For the same reason, it is unlikely that these reefs interact directly with the reefs within the Gulf. In the interior of the Gulf there are other formations that do not reach the surface of the sea and do not originate from reefs, characterized by limited or no accretion capacity, despite possibly being densely colonized by coral biota. Such is the case of the submerged banks that form the Middle Grounds in the northwestern part of the Florida shelf and, in particular that of the numerous diapiric banks such as Flower Gardens along the edge of the Texas and Louisiana continental shelf (Rezak et al. 1990). Furthermore, these banks are in relatively deep locations (20 m or more), and the environmental conditions that surround them are rather peculiar, resulting in the absence of Acropora corals, one of the most important reef builders, and gorgonians, another common component of Caribbean reefs. In the internal basin of the Gulf, there are also some “deep reefs” hundreds of meters below the surface that, in reality, do not have a reef matrix, but are dense communities of non-symbiotic coral, such as Lophelia.