Future impacts of reduced freshwater inflow and sea level rise on forage fish and their predators in Apalachicola Bay, Florida

Abstract

Estuarine ecosystems often support large populations of forage fish, but these small-medium sized fish and the predators they feed may be affected by multiple climate change and human-induced stressors. In the Apalachicola Bay estuary, Florida, USA, reduced freshwater inflow and sea level rise are two prevalent stressors, and little is known about how these environmental changes might impact the forage fish species who inhabit the estuary. This study uses a food web model for Apalachicola Bay to simulate the impacts of future changes in water temperature and salinity on forage fish and predator species who inhabit the estuary. Water temperature and salinity conditions were based on previously developed simulations of reduced freshwater inflow and sea level rise in Apalachicola Bay from 2020 to 2049. These simulated environmental changes were applied as forcing functions in the food web model to drive shifts in species biomasses over time. This study centered on changes in biomass for two highly abundant forage fish species, juvenile silver perch (Bairdiella chrysoura) and juvenile pinfish (Lagodon rhomboides), as well as their major predators, spotted seatrout (Cynoscion nebulosus) and inshore lizardfish (Synodus foetens). These changes were assessed at both 10- and 30-year time intervals relative to 2019, along with an examination of forage fish consumption by their predators. Juvenile silver perch biomass increased across all scenarios and time scales, while juvenile pinfish biomass decreased. Consumption of juvenile silver perch by spotted seatrout increased across all scenarios and time scales, and consumption of juvenile pinfish by inshore lizardfish decreased, in concordance with the trends in prey biomass. Both spotted seatrout and inshore lizardfish biomasses decreased across future scenarios, though the high biomass of juvenile silver perch may have played a role in stabilizing the decline of spotted seatrout. Changes in forage fish biomasses and their impacts on predator species as a result of reduced freshwater inflow and sea level rise have implications for ecosystem productivity and the fisheries of the region.