Effects of Increasing Storm Surge on Fish Assemblages and Restoration of Submersed Aquatic Vegetation in a Coastal River

Saltwater intrusion is increasing in frequency and severity in coastal rivers worldwide, with concurrent changes to riverine and riparian communities. In Kings Bay, Florida, USA, a headwater embayment of an 11-km coastal river along the Gulf Coast of Florida, coverage of freshwater, submersed aquatic vegetation (SAV) has historically been influenced by storm surge, eutrophication, and restoration efforts. Recently (2021–2022), Eelgrass Vallisneria spp. frequency of occurrence increased to 73% following restoration efforts that included Eelgrass plantings. However, storm surges associated with three hurricanes (2023–2024) led to declines in total SAV coverage including Eelgrass to near zero, which was new to the system. Analysis of a fish monitoring dataset (2013–2017, 2022, and 2024) and diet sampling of large-bodied fishes (2022–2024) found that when Eelgrass occurrence exceeded 50%, the system was dominated by freshwater fauna such as Florida Bass Micropterus salmoides, Spotted Sunfish Lepomis punctatus, killifishes Fundulidae, and grass shrimps Palaemonidae. When Eelgrass occurrence was below 20% and during periods that followed storm surges, the system was dominated by estuarine fauna such as Tidewater Mojarra Eucinostomus harengulus, Striped Mullet Mugil cephalus, Common Snook Centropomus undecimalis, and swimming crabs Portunidae. The high salinity associated with storm surges experienced during this study quickly overwhelmed all SAV present, including those used in restoration, which in turn affected fish assemblages. These findings will need to be considered as managers and restoration practitioners weigh restoration options against the likelihoods of increased storm frequency and rates of sea level rise.