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Algal community structure of the East and West Flower Gardens, northwestern Gulf of Mexico.

Article Excerpt
Abstract.--The Flower Garden Banks are located approximately 200 km south of the border between Texas and Louisiana, on the outer continental shelf, beginning at a depth of approximately 20 m. The algal community has not been comprehensively evaluated and only checklists of a few dominant macroalgal species have been reported. This study utilized both destructive and non-destructive techniques to characterize the algal community structure. Harvest and photogrammetric samples were collected during two trips to the Flower Garden Banks in October 1998 and March 1999. A total of forty 0.25 [m.sup.2] quadrats of standing stock material were randomly collected, curated and stored for further evaluation. Photogrammetric samples (161) were obtained using an underwater camera and were evaluated by a grid of 25 random points. A total of 4,025 points of information were used to calculate percent composition and cover. Harvest sampling was used to characterize the algal composition of the 'red algal mat' which was the dominant feature comprising 38.4% of the photogrammetric samples. A total of 44 species were identified from the samples. The 'red algal mat' was primarily composed of members of the Order Ceramiales (Centroceras, Ceramium, Hypoglossum, Polysiphonia and Anotrichium).

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The Flower Garden Banks are deep-water coral habitats located on the edge of the outer continental shelf in the northwestern Gulf of Mexico and cover an area of 143 [km.sup.2]. The Flower Garden Banks are found at approximately 18-36 m below the water surface and extend down to 100-150 m (Lugo-Fernandez et al. 2001). The Flower Garden Banks are separated into the East Flower Gardens and the West Flower Gardens and are 12-15 km apart. They were designated as a protected National Marine Sanctuary in 1992. The East Flower Garden Bank is located at 27[degrees] 54.5' N latitude and 93[degrees] 36.0' W longitude, approximately 193 km southeast of Galveston, Texas. The West Flower Garden Bank is located approximately 172 km southeast of Galveston, Texas at 27[degrees] 52.4' N latitude and 93[degrees] 48.8' W longitude (Fig. 1).

[FIGURE 1 OMITTED]

Both banks are topographic features created by the uplift of underlying salt domes of Jurassic, Louann origin (Rezak 1981). Bedrock material above the domes is covered with an overgrowth of calcareous marine organisms and represents the largest charted calcareous banks in the northwestern Gulf of Mexico (Bright et al. 1985) and the northernmost coral reefs on the continental shelf of North America (Bright et al. 1984). The Flower Garden Banks are part of a widely dispersed and discontinuous are of reef material located along the outer continental shelf of the Gulf of Mexico (Rezak et al. 1985). The diversity of the coral community at the Flower Garden Banks has been described as depauperate as it supports only 20 species of hermatypic corals (Bright et al. 1984; Lugo-Fernandez et al. 2001). Although low diversity communities exist on neighboring banks, the reefs adjacent to Cabo Rojo, approximately 100 km south of Tampico, Mexico are the closest extensively developed coral reefs in the Gulf of Mexico and make up...

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