Abstract
The ecology of estuaries is shaped significantly by the extent of freshwater discharge which regulates abiotic processes and influences overall biological productivity. The Suwannee River Estuary of Florida’s Big Bend Coastline has historically been a productive and diverse estuarine ecosystem supported by significant freshwater inputs from the Suwannee River. In recent years, significant changes in land use and climatic conditions have resulted in lower discharges from the Suwannee. Our objectives were to explore the impact of freshwater inputs from the Suwannee River on the estuarine forage fish and sportfish communities downstream. We built a trophic-dynamic food web model in Ecopath with Ecosim to simulate different levels of discharge and evaluate how changes in discharge (drought and floods) would influence the trophic structure of the food web. Using the fitted model, we applied a series of different short-term and long-term flow projections under different climatic scenarios to evaluate impacts on fish functional groups and sportfish biomass. Simulations suggested that ecological production was more influenced by drought conditions than flood conditions. In our short-term scenarios, the drought simulations produced biomass changes that were approximately twice as substantial as the flood scenarios. When making comparisons to other published EwE models, we generally observed smaller changes in biomass production. Although this model focused on the influence of bottom-up effects, we observed strong top-down control of snook (Centropomus undecimalis) on the system. Several functional groups were particularly sensitive to changes in snook abundance which included spotted seatrout (Cynoscion nebulosus), sand seatrout (C. arenarius), and other members of the familySciaenidae. Because snook have recently colonized the estuary, likely as a result of warmer winter temperatures, this finding has implications for climate change and natural resource management.
Highlights
Estuarine ecosystems are shaped significantly by the frequency and magnitude of freshwater inputs which can have an impact at the organismal level and lead to broad ecological effects (Paerl, 2006; Baptista et al, 2010; Piazza and La Peyre, 2011)
Our analysis focused on how forage fish and recreationally important fish species will be impacted through trophic interactions that are altered with changes in river discharge
Our analysis indicated that drought conditions had a greater impact on ecological production than flood conditions
Summary
Estuarine ecosystems are shaped significantly by the frequency and magnitude of freshwater inputs which can have an impact at the organismal level and lead to broad ecological effects (Paerl, 2006; Baptista et al, 2010; Piazza and La Peyre, 2011). The major factors that influence discharge from riverine systems are precipitation patterns and anthropogenic extraction. Discharge Impacts on Estuarine Fish change models predict significant variability in future precipitation and evapotranspiration rates, which will likely have strong impacts on riverine flow (Walther et al, 2002; Milly et al, 2005; Trenberth, 2011). Many rivers have experienced significant freshwater withdrawals for energy and agricultural purposes (Poff et al, 1997). These alterations often decrease the frequency and intensity of high flow events and modify overall discharge variability that is characteristic of estuarine systems downstream (Alber, 2002). Understanding how changes in river discharge will affect estuarine ecosystems is critical to management of the animal species inhabiting estuaries, with implications for conservation of ecosystem services that estuaries provide
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