Coral Reefs of the Southern Gulf of Mexico

Chapter 2. Reef Distribution

Reef Distribution John W. Tunnell Jr. There are 46 named coral reefs in the southern Gulf of Mexico. Of these, 31 are the Veracruz Shelf reefs (VSR) in the southwestern Gulf off the state of Veracruz, and 15 are the Campeche Bank reefs (CBR) in the southeastern Gulf (Table 2.1, Fig. 2.1). Other named and unnamed shoals and banks have yet to be explored; these likely have coral communities as well. Dahlgren (1993), for instance, lists approximately 10 named and more than 25 unnamed banks (topographic highs and reefs) on the Campeche Bank for which there is little or no scientific information. Coral reefs in the southwestern Gulf are typically located nearshore (200 m) to mid-shelf (22 km) on a narrow terrigenous continental shelf (Morelock and Koenig 1967). The climate here is subhumid to humid and has high rainfall and substantial mainland drainage. In the southeastern Gulf, reefs are located on a wide carbonate shelf, primarily along the 55 m contour on the outer shelf, and range from 130 to more than 200 km offshore (Tunnell 1992). In contrast to the southwestern Gulf, the climate here is semiarid. The southeastern Gulf reefs are surrounded by oceanic Caribbean waters from the Yucatán Channel and are not affected by mainland drainage. The southern Gulf reefs are submerged “mountain -like” structures scattered across the continental shelf, in contrast to the scattered patch reefs in nearby low-energy coastal areas such as the Florida Keys and Belize, where mangroves line the shoreline and seagrasses predominate as submarine vegetation nearshore. Mainland shorelines are moderate-energy sandy beaches or rocky shores (volcanic) in the southwestern Gulf and low-energy sandy beaches or rocky shores (limestone) in the southeastern Gulf. The southwestern Gulf coral reefs are clustered in two systems, each within two subgroups: the Tuxpan Reef System (TRS) and Veracruz Reef System (VRS). To the north there are six emergent platform reefs in the TRS, three of which are grouped off Cabo Rojo and three northeast of Tuxpan (Fig. 2.2). Isla de Lobos Reef is the only one in the TRS that has an island, and consequently is the best known because the island has served as an adequate base camp for extended expeditions (e.g., Rigby and McIntire 1966; Chávez et al. 1970; Ray 1974; Tunnell 1974; Roberts 1981; Allen 1982). Blanquilla Reef is the most northerly emergent coral reef in the western Gulf of Mexico (Moore 1958). The VRS in the far southwestern Gulf of Mexico comprises 25 coral reefs in two subgroups, one consisting of smaller reefs nearshore and one with mostly larger reefs extending farther offshore (Fig. 2.3). The first, or northern, group of 13 reefs lies offshore from the city of Veracruz (Fig. 2.4) and is composed of eight emergent platform reefs (Gallequilla, Anegada de Adentro, La Blanquilla, La Gallega, Pájaros, Isla Verde, Tierra Nueva, and Isla Sacrificios), two submerged bank reefs (or submerged patch reefs Bajo Mersey and Lavandera), and three fringing reefs (Punta Gorda–Punta Majahua, Hornos, and Punta Mocambo). 2 A4339.indb 14 A4339.indb 14 7/6/07 11:18:43 AM 7/6/07 11:18:43 AM Table 2.1. Data on southern Gulf of Mexico coral reefs. Reef name Reef Size 2 Distance 3 Islands 4 Geographic position 5 Depth 6 (m) type 1 Length (m) Width (m) to mainland (km) Latitude Longitude Tuxpan Reef System (southwestern Gulf) Blanquilla EP 739 500 5 0 21°30’14” 97°10’39” 0–45 Medio EP 500 – 8 0 21°30’02” 97°10’30” 0–45 Isla de Lobos EP 1,950 1,100 11 1 21°20’18” 97°10’21” 0–45 Tanguijo EP 500 – 9 0 21°00’41” 97°10’44” 0–24 Enmedio EP 500 – 9 0 21°00’27” 97°10’36” 0–24 Tuxpan EP 500 – 11 0 21°00’08” 97°10’11” 0–24 Veracruz Reef System (southwestern Gulf) Northern Reefs (off city of Veracruz) Punta Gorda– Punta Majahua F 3,800 375 0 0 19°14’33” 96°10’34” 0–4 Galleguilla EP 1,000 375 2 0 19°13’53” 96°07’24” 0–18 Anegada de Adentro EP 1,870 500 8 0 19°13’35” 96°03’22” 0–36 La Blanquilla EP 625 625 4 1 19°13’35” 96°05’49” 0–24 La Gallega EP 2,370 1,125 0 0 19°13’23” 96°07’39” 0–12...