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Yurek S, Eaton MJ, Lavaud R, Laney RW, DeAngelis D, Pine III, WE, La Peyre MK, Martin J, Frederick P, Wang H, Lowe MR, Johnson F, Camp EV, Mordecai R. 2021 Modeling structural mechanics of oyster reef self-organization including environmental constraints and community interactions. Ecological Modelling 440:109389
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Abstract
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January 2021
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Self-organization in reef-building systems is a process of establishing reef morphology on aquatic landscapes from substrate generated by the population, and reinforcing these structures through interactions between internal processes and external factors. In oyster reefs, internal dynamics include production of calcareous shell, which serves as settlement substrate for larval recruits. External factors include environmental conditions and predation, which regulate overall population size through growth and mortality, but also regulate settlement dynamics by exposing interior shell surfaces through mortality. Oyster reefs are also highly spatially constrained by aquatic conditions, thus their efficiency for producing settlement habitat under these constraints may be critical to self-organization and long term persistence. We developed an individual based model that simulates engineering of oyster reefs through individual contributions of shell, which slowly degrade and consolidate to form reef structure. Reef habitat has two aspects in this model, one for elevating the population above the benthos, and another for making exposed shell surfaces available for settlement. We applied the model to examine how these two aspects relate to the live population as a coupled system with complex feedbacks. In particular, we examined how temporal dynamics of the reef proceed through time as the size structure of the live population and relative composition of shell types change through time. To represent these dynamics, we simulated single restoration events and tracked ensuing dynamics over subsequent decades without additional enhancement, for an example study site in South Carolina (USA). To estimate uncertainty in restoration performance, we followed a biological ensemble modeling approach, varying selected model parameters over five scenarios of predator community composition. Our goal was to identify trends that were robust across simulations, which could serve as hypotheses and predictions for future field studies. The overall temporal pattern of simulations was three distinct phases: initial transient dynamics of the stocked population, followed by growth and saturation of the life population, and then saturation of settlement habitat several years later. All simulations incurred considerable loss of shell biomass during the transient phase when the live population was establishing and shell degradation exceeded production. Simulations with predators were able to recover from this decline through production of live oysters, while simulations without predators continued to decline throughout simulation runs. These results indicate that reefs can be productive with respect to the live population, but decline overall in reef substrate. We conclude with hypotheses relating the efficiency of generation of settlement habitat to measures of biomass and individual density, which suggest levels that may lead to reef self-organization.
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Lavaud R, La Peyre MK, Couvillion B, Beseres Pollack J, Brown V, Palmer T, Keim B. Predicting restoration and aquaculture potential of an ecological engineer through an eco-physiological mechanistic model. Ecological Modeling
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Abstract
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December 2023
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A simple, non-negotiable truth of ensuring success in restoration of ecological engineers (EE) and the functions they support remains the need for the focal species to survive, grow and reproduce. The use of mechanistic modeling, such as a dynamic energy budget (DEB), to map an EE’s fundamental niche provides supports restoration and management predictive of EE resilience under current and future conditions. One EE, the eastern oyster, <i>Crassostrea virginica</i>, provides critical estuarine habitat, and supports a valuable fishery across the northern Gulf of Mexico. Recent declines in oyster populations in this region from human activities, as well as short-term and extreme events have led to significant efforts to restore wild, self-sustaining broodstock reefs, and develop off-bottom aquaculture. To explore potential outcomes for oyster restoration and aquaculture development, we used an individual bioenergetic model based on DEB theory to derive an aquaculture index, based on survival and time to market size, and restoration index, based on survival and reproductive output, across six key Texas and Louisiana estuaries under current (2014–2020) and future predicted environmental conditions (2041–2050). Aquaculture scores using daily averaged current conditions reproduce an observed gradient of oyster growth success increasing from upper estuary to offshore areas, with lower variation in Texas estuaries compared to Louisiana. Restoration scores under daily averaged current conditions showed similar trends with more variability than the aquaculture index due to spawning potential, which is of importance for reef sustainability. In general, Louisiana estuaries showed higher growth rates, and reproduction compared to Texas estuaries, but due to the higher variability and more frequent extremes in salinity and temperature, Louisiana estuaries were more likely to experience mortal conditions any given year, as compared to Texas estuaries. Comparison between current and future conditions indicated that oyster aquaculture and restoration potential in presently occupied areas will possibly decrease in a future climate. However, the spatial resolution of currently available climate model outputs within coastal and estuarine areas limits planning information. This represent a necessary area of improvement to better evaluate the physiological response of EE to future conditions, especially since most aquaculture and restoration developments are likely to occur close to the coastline. Finally, this work demonstrates the potential of mechanistic modeling to inform future planning under environmental conditions likely not currently within the realized niche of EE.
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Lavaud R, La Peyre MK et al. 2023. Final Project Report: A roadmap for developing resilient coastal shellfish populations: using spatial and process-based modeling for restoration under current and predicted future water quality conditions. DOI Climate Adaptation Center FInal Report.
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Abstract
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August 2024
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Our estuaries support valuable recreation, fisheries and aquaculture dependent on healthy and vibrant ecosystems. Along the northern Gulf of Mexico (nGoM), estuaries sustain local economies through their high productivity. At the same time, they receive over 50% of the US watershed discharge, and water quality within these estuaries is impacted by local management of rivers, and climate change. Within nGoM estuaries, eastern oysters serve as both critical fisheries, and ecosystem engineers, providing nursery and feeding grounds, and improving water quality. Recent declines in oyster populations from anthropogenic activities and extreme events have led to significant efforts to restore wild, self-sustaining broodstock reefs, and develop aquaculture. In this project we extended a model predicting oyster survival, growth and reproduction across 6 important oyster growing estuaries in Texas and Louisiana. We used this model to provide restoration and aquaculture suitability scores within the coastal waters to help inform managers and the oyster industry. The resulting suitability scores reflect likelihood of oyster survival and reproduction (restoration) and likelihood of oyster growth and survival (aquaculture) under current and future (2041-2050) conditions. Louisiana estuaries showed higher growth rates and reproduction than Texas estuaries, but due to the higher variability and more frequent extremes in salinity and temperature, Louisiana estuaries were more likely to experience mortal conditions. Comparison between current and future conditions indicated that oyster aquaculture and restoration potential in presently occupied areas might decrease in the future; however, the spatial resolution of currently available climate model outputs within coastal and estuarine areas limits planning information. These suitability maps help managers and stakeholders assess the current and future value of specific locations for oyster restoration and aquaculture. This work also identifies the need for improved within-estuary water quality projections and highlights the need to continue to quantify oyster responses to extreme and novel conditions.
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La Peyre, M.K., Marshall, D.A., and Sable, S.E., 2021, Oyster model inventory: Identifying critical data and modeling approaches to support restoration of oyster reefs in coastal U.S. Gulf of Mexico waters: U.S. Geological SurveyOpen-File Report 2021–1063, 40 p., https://doi.org/10.3133/ofr20211063.
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August 2021
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