Predicting restoration and aquaculture potential of eastern oysters through an eco-physiological mechanistic model

A simple, non-negotiable truth of ensuring success in the restoration of ecological engineers (EE) and the functions they support is the need for the focal species to survive, grow and reproduce. Using mechanistic modeling, such as a dynamic energy budget (DEB), to map an EE's fundamental niche supports restoration and management predictive of EE resilience under current and future conditions. One EE, the eastern oyster, Crassostrea virginica, provides critical estuarine habitat and supports a valuable fishery across the northern Gulf of Mexico. Recent declines in oyster populations in this region from anthropogenic activities 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 a restoration index, based on survival and reproductive output. The model was run across six major Texas and Louisiana estuaries under current (2014-2020) and future (2041-2050) projected environmental conditions. Aquaculture scores using daily averaged current conditions reproduce an observed gradient of oyster growth success increasing from the upper estuary to lower estuary (Texas) or offshore areas (Louisiana), with lower variation occurring in Texas estuaries. Restoration scores under daily averaged current conditions showed similar trends with more variability than the aquaculture index due to spawning potential, which is important for reef sustainability. In general, 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 in 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 might decrease in the future; however, the spatial resolution of currently available climate model outputs within coastal and estuarine areas limits planning information. Addressing this gap represents a necessary 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 not currently within the realized niche of EE.