Developing an Oyster Metapopulation Model for Louisiana Estuaries to Assess Reef Connectivity, Recruitment, and Sustainability in support of Louisiana Monitoring and Adaptive Management Strategy
USGS and collaborators are co-producing integrated oceanographic and ecological modeling to support decision making in Louisiana estuaries.
The Science Issue and Relevance: The Eastern oyster (Crassostrea virginica) is a reef-building species that provides numerous important ecosystem services, such as creation and stabilization of benthic habitat structure, water filtration, mitigation of shoreline erosion, and exchange of energy and nutrients between the seafloor and aquatic food webs. Eastern oysters are also commercially and recreationally important. The State of Louisiana alone contributes ~36% of annual landings in the U.S. (market value, LDWF 2022). However, oyster populations in the northern Gulf have experienced considerable decline. To counteract this trend, the Louisiana Department of Wildlife and Fisheries (LDWF) is investing in oyster restoration across managed areas. Many oyster reefs in Louisiana are linked together as networks by circulation of water and larvae throughout coastal basins, referred to as ‘metapopulations’. Environmental variation through changes in water flow leads to dynamic changes in local conditions at reefs. For these reasons, a key focus is managing reefs to support sustained natural reproduction and recruitment across this environmental variation, while maintaining productivity of the reef networks on the whole. This process involves identifying areas that are likely to have the highest impact on oyster population connectivity statewide, and establishing and maintaining broodstock sanctuaries in those areas.
Methodology for Addressing the Issue: USGS is collaborating with LDWF, the Louisiana Coastal Protection and Restoration Authority (CPRA), Dynamic Solutions, LLC, the University of Maryland, Louisiana State University, and the Water Institute of the Gulf, to co-produce integrated oceanographic and ecological modeling to answer these management and research questions: What are optimal management strategies for sustaining oyster reef networks in coastal basins, and where are optimal locations for establishing broodstock and/or sanctuary reefs? This requires better understanding of the physical and ecological factors that drive basin-scale oyster population dynamics, such as production and recruitment. To do this, the research team is developing a process-based metapopulation model that couples a suite of hydrodynamic and water quality models (“Hydro”) with larval transport models (“Transport”) and on-reef individual based oyster models (“Reef”) to support decision making in Louisiana estuaries. Environmental variables generated by the Hydro model force the Transport model, which simulates oyster larval settlement over space and time. The Reef model also uses environmental variables from the Hydro model to compute individual oyster bioenergetics on the reef, and uses larval settlement from the Transport model to determine population dynamics. Finally, the Reef model provides larvae through spawning to the Transport model, which simulates their dispersal.
Future Steps: This modeling platform will provide a tool that managers of Louisiana coastal estuaries can apply to examine reef connectivity through larval transport, and to understand linkages between reefs of different densities and size classes, including larval provision, and recruitment across space and time. Taking a metapopulation approach develops a context for predicting impacts of water management (streamflow diversions) and environmental change (tropical storms, drought, floods) across managed coastal basins. In this way, management of oysters can move from individual reef level to assessment of a network or metapopulation of reefs under current and future predicted conditions.
This modeling platform will enable informed decisions aimed at achieving fundamental objectives of the Louisiana Trustee Implementation Group (TIG) and associated SMART objectives (Specific, Measurable, Achievable, Relevant, Timeline) outlined in the Deepwater Horizon (DWH) oil spill Final Programmatic Damage Assessment and Restoration Plan and Final Programmatic Environmental Impact Statement (PDARP/PEIS). These high-level objectives include balancing growth of oyster populations on Natural Resource Damage Assessment (NRDA)-enhanced and restored reefs with ecologically sustainable public harvesting, and spatially connecting source and sink reefs for larval transport to foster resilience and sustainability of oyster populations. These activities meet these high-level oyster SMART objectives by providing output that will enable LDWF to evaluate locations for oyster cultch plants and broodstock reefs. More information on the SMART Objectives of the Louisiana Monitoring and Adaptive Management Strategy can be found here: https://www.fws.gov/doiddata/dwh-ar-documents/3443/DWH-ARZ009746.pdf
USGS and collaborators are co-producing integrated oceanographic and ecological modeling to support decision making in Louisiana estuaries.
The Science Issue and Relevance: The Eastern oyster (Crassostrea virginica) is a reef-building species that provides numerous important ecosystem services, such as creation and stabilization of benthic habitat structure, water filtration, mitigation of shoreline erosion, and exchange of energy and nutrients between the seafloor and aquatic food webs. Eastern oysters are also commercially and recreationally important. The State of Louisiana alone contributes ~36% of annual landings in the U.S. (market value, LDWF 2022). However, oyster populations in the northern Gulf have experienced considerable decline. To counteract this trend, the Louisiana Department of Wildlife and Fisheries (LDWF) is investing in oyster restoration across managed areas. Many oyster reefs in Louisiana are linked together as networks by circulation of water and larvae throughout coastal basins, referred to as ‘metapopulations’. Environmental variation through changes in water flow leads to dynamic changes in local conditions at reefs. For these reasons, a key focus is managing reefs to support sustained natural reproduction and recruitment across this environmental variation, while maintaining productivity of the reef networks on the whole. This process involves identifying areas that are likely to have the highest impact on oyster population connectivity statewide, and establishing and maintaining broodstock sanctuaries in those areas.
Methodology for Addressing the Issue: USGS is collaborating with LDWF, the Louisiana Coastal Protection and Restoration Authority (CPRA), Dynamic Solutions, LLC, the University of Maryland, Louisiana State University, and the Water Institute of the Gulf, to co-produce integrated oceanographic and ecological modeling to answer these management and research questions: What are optimal management strategies for sustaining oyster reef networks in coastal basins, and where are optimal locations for establishing broodstock and/or sanctuary reefs? This requires better understanding of the physical and ecological factors that drive basin-scale oyster population dynamics, such as production and recruitment. To do this, the research team is developing a process-based metapopulation model that couples a suite of hydrodynamic and water quality models (“Hydro”) with larval transport models (“Transport”) and on-reef individual based oyster models (“Reef”) to support decision making in Louisiana estuaries. Environmental variables generated by the Hydro model force the Transport model, which simulates oyster larval settlement over space and time. The Reef model also uses environmental variables from the Hydro model to compute individual oyster bioenergetics on the reef, and uses larval settlement from the Transport model to determine population dynamics. Finally, the Reef model provides larvae through spawning to the Transport model, which simulates their dispersal.
Future Steps: This modeling platform will provide a tool that managers of Louisiana coastal estuaries can apply to examine reef connectivity through larval transport, and to understand linkages between reefs of different densities and size classes, including larval provision, and recruitment across space and time. Taking a metapopulation approach develops a context for predicting impacts of water management (streamflow diversions) and environmental change (tropical storms, drought, floods) across managed coastal basins. In this way, management of oysters can move from individual reef level to assessment of a network or metapopulation of reefs under current and future predicted conditions.
This modeling platform will enable informed decisions aimed at achieving fundamental objectives of the Louisiana Trustee Implementation Group (TIG) and associated SMART objectives (Specific, Measurable, Achievable, Relevant, Timeline) outlined in the Deepwater Horizon (DWH) oil spill Final Programmatic Damage Assessment and Restoration Plan and Final Programmatic Environmental Impact Statement (PDARP/PEIS). These high-level objectives include balancing growth of oyster populations on Natural Resource Damage Assessment (NRDA)-enhanced and restored reefs with ecologically sustainable public harvesting, and spatially connecting source and sink reefs for larval transport to foster resilience and sustainability of oyster populations. These activities meet these high-level oyster SMART objectives by providing output that will enable LDWF to evaluate locations for oyster cultch plants and broodstock reefs. More information on the SMART Objectives of the Louisiana Monitoring and Adaptive Management Strategy can be found here: https://www.fws.gov/doiddata/dwh-ar-documents/3443/DWH-ARZ009746.pdf