Using linked models to evaluate effects of nutrient and hypoxia reductions on living marine resources
28 February 2023, 17:30 CEST (Brussels, Amsterdam, Madrid)
Expansive hypoxia in the Northern Gulf of Mexico (NGOMEX) will continue to affect living resources, but the magnitude, predictability and even the direction of these effects are not well quantified. To evaluate effects of hypoxia on fish and fisheries, an Ecospace model was developed representing 60 groups of the NGOMEX food web. The model is linked to a physical-biological ROMS model from which it receives dissolved oxygen, temperature, salinity, and phytoplankton at each timestep using the spatial-temporal framework in Ecospace. After initial simulations emphasized the importance of (bottom-up) food web dynamics when evaluating effects of nutrient loading and hypoxia on NGOMEX living resources, the current focus is on simulating nutrient load reduction goals set by the Mississippi River/Gulf of Mexico Hypoxia Task Force to reduce hypoxia. The coupled model was calibrated using existing conditions from 2000-2016, after which scenarios for short-term and long-term hypoxia reduction were explored: The short-term goal of a 20% reduction in nitrogen and phosphorus load by 2025, and the long-term goal of reducing the hypoxic area to 5000 km2 by 2035. Novel spatial Monte-Carlo simulations were performed to estimate the uncertainty of the predictions. IBM mode in Ecospace was used (where fish move in packets as super-individuals) to ensures species in the model derive their consumption and mortality rates from the conditions in each local cell, which much improves predictions that involve localized stressors. Output shows that fisheries species biomass changes in response to nutrient load reductions are small and species-specific, and that this is the result of the combined positive effects of hypoxia reductions and negative effects of nutrient reductions (reducing secondary productivity). The overarching goal of the coupled modelling approach is improving the capability to assess effects of alternative management strategies on ecosystem function, living resources, and fisheries.
Kim de Mutsert is an Assistant Professor in the Division of Coastal Sciences of the School of Ocean Science and Engineering at The University of Southern Mississippi. She holds a PhD in Oceanography and Coastal Sciences from Louisiana State University and an MS in Biology from the University of Amsterdam. Her research focus is coastal and estuarine fish ecology. She studies the effects of environmental and anthropogenic stressors on nekton abundance, community structure, food web dynamics and fisheries. Examples of stressors included in her studies are eutrophication, oil pollution, habitat alteration, land loss, climate change, hypoxia, and changes in freshwater discharge. She uses a combination of field monitoring, lab studies, and ecosystem modelling in her projects.