Changes in the distribution of seagrass species along Florida's central Gulf Coast: Iverson and Bittaker revisited

A broad-scale survey of seagrass species composition and distribution along Florida's central Gulf Coast (known as the Big Bend region) was conducted in the summer of 2000 to address growing concerns over the potential effects of increased nutrient loading from adjacent coastal rivers. Iverson and Bittaker (1986) originally surveyed seagrass distribution in this region between 1974-1980. We revisited 188 stations from the original survey, recording the presence or absence of all seagrass species. Although factors such as accuracy of station relocation, differences in sampling effort among studies, and length of time between surveys preclude statistical comparisons, several interesting patterns emerged. While the total number of stations occupied by the three most common seagrass species, Thalassia testudinum, Syringodium filiforme, and Halodule wrightii, was similar between the two time periods, we observed a change in the number of records of each species as well as changes in distribution with depth. T. testudinum and Halophila engelmanni occurrence declined in the deepest areas of the region, while the number of stations occupied by S. filiforme and H. wrightii increased in nearby areas. We observed several localized areas of seagrass loss, frequently associated with the mouths of coastal rivers. These results suggest that increased nutrient loading to coastal rivers that discharge into the Big Bend area may be affecting seagrasses by increasing phytoplankton abundance in the water column, thus changing water clarity characteristics of the region.