XVI International Botanical Congess

There is limited understanding of spatial and temporal variability in thecomposition and abundance of macroalgal communities in coral reefs. A synoptic snapshot view at 20 reefs along the Florida Reef Tract (1995) found a large amount of inter-reef variability in the macroalgal community, dominated by Dictyota spp. and Halimeda spp. More intensive sampling of permanent photo-quadrats at Molasses Reef, off Key Largo, Florida, indicated substantial temporal variability, including large differences among seasons, years, and decades (1985-1988 vs. 1995-1996). This variability is probably controlled by both bottom-up (nutrients) and top-down (herbivory) controls, which may be altered by anthropogenic activities. These activities may result in further changes in reef community structure, with serious impact on ecosystem structure and function.