ABSTRACT
Historical (pre-1930s) seagrass meadows in Tampa Bay are believed to have covered 31,000 ha of the shallow bay bottom. However, impacts to the bay from increasing population and industrial development of the Tampa Bay area resulted in large seagrass reductions. By 1982, approximately 8,800 ha of seagrass remained. Recently, Tampa Bay seagrass monitoring programs have shown that the trend of seagrass loss has been reversed. The bay-wide seagrass cover in 1997, was estimated at 10,930 ha. In Hillsborough Bay, the bay segment that historically has had the poorest water quality, seagrass increased from near 0 ha in 1984 to about 57 ha in 1998. The Tampa Bay seagrass expansion apparently started in response to water quality improvements that occurred from the late 1970s to the mid-1980s, which included reductions in phytoplankton biomass and water column light attenuation. These improvements followed a nearly 50% reduction in external nitrogen loading from domestic and industrial point-sources, primarily discharging to Hillsborough Bay, that occurred in the early 1980s. However, most recently, high rainfall amounts during the years 1995, 1996, and the 1997-1998 El Niño event increased nitrogen loading to the bay. Both phytoplankton biomass and light attenuation increased in all major bay segments during this period of high rainfall. These influences on seagrass growth are often detrimental and appear to have reduced the rate of seagrass expansion during the last few years.
