Using an Individual-Based Model to Predict the Genetic Impacts of Hatchery Based Restoration of the Eastern Oyster (Crassostrea virginica) in Chesapeake Bay
Principal Investigator:Louis Plough
Institution:University of Maryland Center for Environmental Science
Co-Principal investigator:Katie Hornick
Strategic focus area:Sustainable fisheries and aquaculture
A century of overfishing, habitat destruction, and disease have left stocks of the Eastern oyster Crassostrea virginica at historically low levels in Chesapeake Bay, prompting wide-ranging restoration efforts. A large hatchery-based supplementation program has been established in Harris Creek on the Choptank River, in which billions of spat produced by the Horn Point Laboratory (HPL) Oyster Hatchery have been planted since 2011. While this effort has been successful in increasing abundance, there has been no genetic monitoring of the restored or proximal wild populations, thus the potential negative genetic impacts of supplemental breeding on the long-term viability and resilience of oyster populations in Harris Creek remains unknown. Furthermore, current models and methods to estimate the effect of hatchery supplementation on wild populations are insufficient for oysters due to complex life-history features that they possess (e.g. overlapping generations). Thus, new models are needed to accurately assess the impact of hatchery supplementation on oyster populations in Harris Creek. In this project we will develop a novel, individual based model (IBM) of oyster population genetics to assess the genetic impact of supplementation, using the metasim package in R. Rmetasim provides a flexible modeling framework for accommodating life history features of oysters as well as the input of a variety of demographic and biological parameters specific to oysters or the Harris Creek population, which will be taken from the literature and from previous or ongoing empirical genetic work. With this model we will examine a range of restoration scenarios, including those with disease mortality, to determine the factors that most greatly affect the maintenance of diversity and determine the current status of Harris Creek populations. We will also estimate the effective size of the wild population in Harris Creek, as it is the only missing parameter needed for our model, using genome-wide genetic marker data (single nucleotide polymorphisms, SNPs). We expect the results of this work to have a direct impact on future restoration efforts in Chesapeake Bay, providing recommendations on how to improve hatchery or stocking practices to increase genetic diversity and thus enhance the sustainability of oyster populations. More broadly, development of a flexible modeling tool for assessing the genetic impact of oyster supplementation may be useful for planning oyster supplementation efforts in other regions. For the outreach program, a series of middle school science units will be created and taught with Julie Harp at Mace’s Middle School, using our integrated empirical and modeling approach as a framework for STEM-focused learning. Students will be exposed to the data collection, input and outputs, using an online interactive version of our completed model to demonstrate the use of various tools to solve complex environmental problems with real-world significance.