Abstract
The Southwest Florida Shelf (SWFS) is a productive and economically important ecosystem threatened by polluted terrigenous inputs including managed discharges from the Caloosahatchee River Estuary (CRE). Yet, the benthic environment of the SWFS is not well characterized and is not regularly monitored. To address this gap in knowledge we monitored water quality, substrate composition, epibenthic biota, and microbial communities at eight SWFS sites every two months from July 2022 to July 2023. Sites were selected at 5, 10, 15, and 20 m depths off Lee County, near the discharge plume of the CRE, and at the same depths off Collier County, south of the plume. The plume was defined as the stretch of continental shelf most heavily influenced by the CRE, with diminished optical water quality. Sampling included periods before and after the passage of major Hurricane Ian in September 2022. Substrate type, depth, and plume proximity influenced water quality and community responses both before and after the hurricane. Notably, the diversity of epibenthos was reduced within the CRE plume, seen in the absence of sensitive taxa. The hurricane also strongly influenced the shelf ecosystem, altering substrate composition and significantly reducing biotic cover, especially at 10 m depth sites. Fleshy macroalgae, calcareous green algae, seagrass, sessile invertebrates, and stony corals suffered substantial losses, while soft coral and sponge communities were more resilient. Post-hurricane, turbidity, dissolved organic matter, and inorganic nutrients increased, while total nitrogen, total phosphorus, and silica decreased. Microbes associated with the nearshore environment shifted offshore in the wake of the hurricane, particularly in the plume region. Changes to freshwater release schedules and increased storage runoff in the C43 reservoir of the CRE watershed should reduce the influence of chronic eutrophication and damaging discharges on the shelf and improve its diversity and resilience.
