ALGAL COMMUNITY STRUCTURE OF THE EAST AND WEST FLOWER GARDEN BANKS, NORTHWESTERN GULF OF MEXICO

Abstract

The algal communities of the Flower Garden Banks National Marine Sanctuary have not been comprehensively evaluated and only a few dominant macroalgal species have been reported. This study utilizes both destructive and non‐destructive sampling techniques to characterize and taxonomically identify the ‘algal mat’ community structure. The East and West Flower Garden Banks are located on the outer continental shelf approximately 200 km off the Texas‐Louisiana coastline. The average depth of both banks is 100 m with the crest approximately 20 m from the surface. Harvest and photogrammetric samples were collected during two extended cruises to the Flower Garden Banks in October 1998 and March 1999. Forty, 0.25‐m2 quadrats of standing stock material were randomly collected along with one hundred sixty‐one 0.25 m2 photo‐quadrats from an average depth of 27 m. Photo‐transparencies were projected to an actual size grid with 25 random points. Four thousand twenty‐five transparency points were evaluated and used to calculate percent composition of algal cover. Harvest samples were used to characterize the “algal mat” composition, species richness, abundance, and biomass. Forty‐two species were identified from the samples representing 14 Orders. The “red algal mat” was the dominant algal coverage comprising 38.4% of all photogrammetric samples. This mat was primarily composed of members from the Order Ceramiales. Centroceras, Ceramium, and Polysiphonia comprised 33.4% of the mat, Anotrichium and Hypoglossum, 22.4%.