Investigating seagrass die-off in Florida Bay

dead and alive seagrass underwater
Dead and surviving turtle grass in Florida Bay.

In summer 2015, massive amounts of seagrass began to die in Florida Bay, the shallow body of water located between the southern end of the Florida peninsula and the Florida Keys. The seagrass die-off caused concern among fishers and ecologists because it jeopardizes recreational fishing in Everglades National Park and the nursery and juvenile habitat for pink shrimp, spiny lobster and many fish species. Because of the ecological value of Florida Bay and its seagrass communities, FWRI scientists have been at the forefront of an interagency effort to document and understand the seagrass mortality, which primarily affected dense stands of turtle grass (Thalassia testudinum) in the western half of Florida Bay. Aerial photography collected in spring 2016 indicates that more than 20,000 acres of seagrass have been affected to varying degrees of loss.

FWRI scientists responded immediately to reports of die-off in July 2015 and determined that the immediate cause of seagrass mortality-toxic levels of sulfide in sediments and water- was the same as a similar seagrass mortality event in Florida Bay in the late 1980s and early 1990s. Now, as then, a local drought and hypersaline conditions contributed to the seagrass mortality. The relationship between climatic events and the build-up of toxic levels of sulfide in seagrass sediments is not clear. However, an extensive latticework of shallow mudbanks restricts water circulation in Florida Bay and likely contributes to the Bay’s vulnerability to high salinity and seagrass mortality.

FWRI scientists are currently assessing the damage and working with partner agencies and universities to monitor natural recovery. Since 1995, the Fisheries Habitat Assessment Program (FHAP) has measured the abundance of seagrass at more than 500 sites in Florida Bay every year. These data show the extent of seagrass loss in 2015 and 2016, and they will serve as benchmarks to monitor future changes in Florida Bay seagrass communities. We are also teasing apart the connections between climate factors and seagrass mortality and hope to accelerate natural recovery and prevent future die-off events. At present, it appears the bay is cooperating with a rapid return to normal salinity ranges, but the plant and animal communities of Florida Bay remain vulnerable to large salinity fluctuations.

 

Additional Information
Publication: Recurrence of Thalassia testudinum seagrass die-off in Florida Bay, USA: initial observations