Exploring Impacts of River Discharge on Forage Fish and Predators Using Ecopath With Ecosim

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 family Sciaenidae. 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.

Exploring multiple stressor effects with Ecopath, Ecosim, and Ecospace: Research designs, modeling techniques, and future directions

“…For example, Booth and Zeller (2005) used Ecotracer to model the accumulation of methyl mercury in the food web and explored interactions with climate change by making metabolic rates temperature dependent. Sinnickson et al (2021) explored the effects of river discharge, affected by droughts and other climate phenomena, on an estuarine ecosystem. Discharge and nutrient concentrations forced primary production, and one species' foraging area was modified by a response function representing general environmental conditions (availability of mangrove habitat and rising temperatures).…”

Identifying trade-offs and reference points in support of ecosystem approaches to managing Gulf of Mexico menhaden

“…The Ecopath with Ecosim (EwE) ecosystem modeling package has been widely used to address a variety of marine resource and ecosystem management challenges (Colleter et al, 2015), including fisheries (Chagaris et al, 2015;Chagaris et al, 2020), invasive species (Chagaris et al, 2017), marine pollution (Walters and Christensen, 2018), habitat alteration (de Mutsert et al, 2021), river discharge and drought conditions (Sinnickson et al, 2021), and climate change (Coll et al, 2020). The modeling framework has been described extensively elsewhere (Christensen and Walters, 2004;Christensen et al, 2005), including best practices (Link, 2010;Heymans et al, 2016), and the software is freely available at www.ecopath.org.…”

Exploring multiple stressor effects with Ecopath, Ecosim, and Ecospace: Research designs, modeling techniques, and future directions

“…A detailed breakdown of modeled stressors and summary of the applied modeling techniques are found in Section 6.3. Capitani et al, 2021a;Christensen et al, 2015;Coll et al, 2016Coll et al, , 2020Corrales et al, 2018Corrales et al, , 2017aCostalago et al, 2019;Dahood et al, 2020Dahood et al, , 2019de Mutsert et al, 2021;Ehrnsten et al, 2019;Field et al, 2006;Fulton, 2011;Fulton et al, 2018;Griffiths et al, 2010;Hernvann et al, 2020;Heymans et al, 2007;Hoover et al, 2013b;Howell et al, 2013;Hyytiäinen et al, 2021;Kumar et al, 2017;Li et al, 2014;Libralato et al, 2015;Lira et al, 2021;Lockerbie and Shannon, 2019;Neira et al, 2009;Niiranen et al, 2013Niiranen et al, , 2012Ortega-Cisneros et al, 2018;Parrish et al, 2012;Pedersen et al, 2021;Serpetti et al, 2017;Shannon et al, 2008;Sinnickson et al, 2021;Smith et al, 2021;Steenbeek et al, 2013;Suprenand and Ainsworth, 2017;Taylor et al, 2008aTaylor et al, , 2008b<...…”

“…For example, Booth and Zeller (2005) used Ecotracer to model the accumulation of methyl mercury in the food web and explored interactions with climate change by making metabolic rates temperature dependent. Sinnickson et al (2021) explored the effects of discharge, affected by droughts and other climate phenomena, on an estuarine ecosystem. River discharge and nutrient concentrations forced primary production, and one species' foraging area was modified by a response function representing general environmental conditions (availability of mangrove habitat and rising temperatures).…”