Extensive and Continuing Loss of Seagrasses in Florida's Big Bend (USA).

Florida's Big Bend in the northeastern Gulf of Mexico contains the second-largest contiguous seagrass meadow in the continental United States, providing numerous ecosystem functions and services, including carbon cycling and storage. We present 21 years of mapping data and 13 years of annual in-water monitoring that reveal extensive declines in area, species frequency of occurrence (FO), and percent cover of seagrass. Seagrass area declined by 15% to 85,170 ha in 2022. Subregions in the southern Big Bend experienced extensive seagrass losses of 90-100%. North of the Steinhatchee River, the Northern Big Bend contained 85% of the total seagrass area and experienced losses of only 8.4%. The FO of seagrass and bare quadrats exhibited similar trends to areal coverage. The lowest FO along with complete loss of species was observed near the mouth of the Suwannee River. At a distance from the Suwannee River, FO also declined, but no species were lost. In the remainder of the Big Bend, FO remained stable except for short-term reductions in 2013-2014, which were likely related to anomalously high runoff from rainfall and tropical storm activity. Mean percent cover, however, declined throughout Big Bend, reaching minimal levels in 2014, with little to no recovery through 2019. The persistence of low percent cover may increase vulnerability of beds to continuing areal losses, but the persistence of seagrass species at a distance from the Suwannee River mouth may allow recovery if environmental conditions improve.