Seasonal and Spatial Variation in Algal Composition and Biomass on the Central Florida Gulf Coast Shelf

Abstract

Information on primary producers is fundamental to the understanding of communities. Little is known about the primary producers of marine communities at intermediate depths on the Florida Gulf Coast shelf. The diversity and biomass of algae and seagrass were studied seasonally at three offshore sites (12- to 18-m depth) and one nearshore site (6-m depth) on the central Florida Gulf Coast shelf. Thirty-eight species of attached and drift macroalgae and one drifting seagrass, Thalassia testudinum, were found. The deepest collection site was the most productive in terms of standing biomass and had much more flora on limestone rubble than on sand. All other sites had relatively low floral biomass. Algal diversity varied considerably with season at 6- and 12-m depths, whereas a more stable diversity was observed at 18m. Plant and algal communities in the Gulf of Mexico vary greatly between sites of different depths even when in close proximity. Intermediate depths contained lower algal biomass with more variable species composition over time than the deeper offshore sites.