Coral Reefs of the Southern Gulf of Mexico

Chapter 8. Reef Corals

Reef Corals Guillermo Horta-Puga, Juan Manuel VargasHern ández, and Juan Pablo Carricart-Ganivet Editors’ note—Coral reef zonation is discussed in chapter 5 and soft and hard coral biodiversity is discussed in chapter 6. Recent distribution of the shallow-water zooxanthellate Scleractinia extends to the greater Indo-Pacific (Pacific and Indian Oceans, Red Sea, and Persian Gulf) and the Atlantic, including the Gulf of Mexico. The greater Indo-Pacific is the most prominent and diverse biogeographic province; the Atlantic is far inferior to the greater Pacific in all aspects of species richness (Wells 1956, 1957; Stehli and Wells 1971; Veron 1995, 2000). During the Cenozoic, the Atlantic Province was physically and genetically connected with the eastern Pacific, sharing numerous coral species. However, by the Pliocene, the Central American Isthmus formed a barrier and separated the two ocean provinces, accelerating local extinction processes that have promoted substantial taxonomic differences between them. The Indo-Pacific is now by far the most diverse in terms of species , genera, and families of reef-building corals, with 700 species. This level of scleractinian diversity arose in a complex, geographically large, and highly heterogeneous environment, isolated from continental land masses that protected the region from the effects of multiple glacial periods. This produced, along with the reticulated evolution, a suite of suitable conditions for the appearance of numerous species since the end of the Mesozoic. The reef fauna that survived in the Atlantic, which is mainly composed of long-lived genera derived from the Tethys fauna, is less diverse today (Veron 1995). The Atlantic Province is characterized by a coral fauna uniformly distributed within all reef areas. It is divided into three subprovinces, Caribbean, Brazil, and Eastern Atlantic, which are characterized mainly in terms of species diversity and/or endemicity (Veron 1995). The Caribbean subprovince contains welldeveloped reefs and is the most diverse, with approximately 70 hermatypic coral species. The other subprovinces have depauperate faunas and some endemic species (Veron 1995). The Gulf of Mexico, a region within the Caribbean subprovince , has lower scleractinian diversity, with only 40 recorded species and no endemic species. Nearly all Gulf of Mexico zooxanthellate corals are restricted to coral reefs, although some species of Porites, Siderastrea, and Montastraea have been seen thriving on nonreef environments, especially in intertidal rocky shores in the coasts of Veracruz, near Punta del Morro and Sontecomapan (G. HortaPuga , personal observation). Reef development in the southern Gulf of Mexico has been achieved in two different geological environments. The western area is a terrigenous sedimentary province. Sediments, derived from eroded materials of the nearby mainland and transported by rivers and streams, are deposited onto the narrow continental shelf (Tunnell 1988; Vargas-Hernández et al. 1993). This depositional environ8 The Ecological Environment A4339.indb 95 A4339.indb 95 7/6/07 11:19:18 AM 7/6/07 11:19:18 AM 96 Horta-Puga, Vargas-Hernández, and Carricart-Ganivet ment precludes any significant nearshore reef development, but not on the adjacent continental shelf, where well-developed platform-type reefs occur. Despite the fact that other physical conditions are suitable for coral reef development, the Veracruz Shelf reefs have developed only in two areas, the Tuxpan Reef System (TRS), offshore near Cabo Rojo and Tuxpan, and the Veracruz Reef System (VRS), off the Port of Veracruz (Britton and Morton 1989; Carricart-Ganivet and Horta-Puga 1993). The TRS is comprised of six platform-type reefs: Blanquilla , Medio, Isla de Lobos, Tanguijo, Isla de Enmedio, and Tuxpan (CarricartGanivet and Horta-Puga 1993). The VRS is by far the most extensive reef area in the Gulf of Mexico, and it is divided into northern and southern groups by the outlet of the Jamapa River, which discharges its waters and suspended materials in the vicinity. The VRS includes three fringing reefs: Punta Gorda, Hornos, and Punta Mocambo and 17 platform-type reefs: Galleguilla, La Gallega, La Blanquilla, Anegada de Adentro, Isla Verde, Pájaros, Isla de Sacrificios, Anegada de Afuera, Isla de Enmedio, Blanca, Chopas, Rizo, Cabezo, Topatillo, Polo, Santiaguillo, and Anegadilla (Carricart-Ganivet and Horta-Puga 1993; VargasHern ández et al. 1993; Gutierrez et al. 1993). The eastern area of the southern Gulf comprises the Campeche Bank reefs, which lie on the wide, shallow continental shelf north and west off the Yucatán Peninsula. This is a carbonate depositional environment, not influenced by important river discharge, although very probably with some intrusions of groundwater. The eastern area includes four major and well-developed platform-type reefs, Alacr...