Distribution, abundance and productivity of seagrasses and macroalgae in Florida Bay

The distribution, abundance, and productivity of submerged macrophytes were measured in Florida Bay to determine the total productivity and seagrass habitat distribution throughout the region. Tha/assia testudinum was widely distributed and was the dominant macrophyte species in the 1,660 km2 of seagrass beds contained in the bay. Ha/odu/e wrighlii was also common, but had standing crop significantly less than Tha/assia at all sample locations. Syringodium fi/iforme grew mainly in areas with strong oceanic influence, especially along the south and west margins of the bay. Macroalgae were a small percentage of the total macrophyte biomass. Gradients in environmental and biological variables extended from southwest to northeast Florida Bay. Water clarity, water exchange, and sediment depth were all greatest in the south and west portion of the bay and decreased towards the northeast comer of the bay. The seagrass standing crop varied from between 60 and 125 g dw·m-2 in the southwest to between 0 and 30 g dw·m-2 in the northeast. Total seagrass leaf standing crop was 8 . 10'0 g dw in Florida Bay, 90% of which was Tha/assia leaf material. Thalassia mean leaf productivity was 0.97 g dw·m-2·d-l, with higher values in the southwest and lower values in the northeast portions of the bay. Approximately I. 7 . 109 gdW'd-1 ofThalassia leaf tissue was produced in Florida Bay during the summer. Tha/assia had about the same leaf productivity on a per gram leaf dry weight basis throughout the different environments of Florida Bay, therefore variations in areal leaf productivity were caused by variations in leaf standing crop and not by variations in leaf specific productivity. Distribution, abundance, and productivity data were used to divide the bay into six community types. A variety of terrestrial and marine habitats form extremely productive, extensive vegetation coverage in south Florida. Seagrass beds, mangrove forests and islands, and coral reefs form the major photoautotrophically-dominated communities which inhabit brackish and salt water environments of the region (Zieman, 1982). The portion of Florida Bay within the Everglades National Park boundaries is about 1,800 km2, most of which is covered with seagrasses (Fig. 1). Mangroves covered about 7% of that area (McNulty et aI., 1972). Areal seagrass coverage in Hawk Channel, in the portion of the bay within the Everglades National Park, and in the area outside of the Park boundary between the Florida keys and the Everglades which extends to the Dry Tortugas, is approximately 5,500 km2 (Iverson and Bittaker, 1986). Seagrasses grow in many shallow coastal areas ofthe world ocean (den Hartog, 1970), however there are only a few locations where seagrass areal coverage as large as in Florida Bay has been reported (Iverson and Bittaker, 1986). Estuarine, lagoon, and coastal habitats are extremely important for the productivity of fisheries and wildlife in south Florida. Extensive submarine seagrass meadows bridge the distances between coral reefs and mangroves, which have widely different physical requirements (Zieman, 1982). Early studies emphasized the role of mangrove habitats as a food source and nursery (Odum and Heald, 1972). The results of more recent investigations suggested that seagrass beds in open water environments and within mangrove-lined bays contained the densest populations of organisms such as the commercially important pink shrimp, Penaeus duorarum (Carter et aI., 1973; Yokel, 1975). A clear association was obtained between organism catch and seagrass cover