This project will address questions that are important for the success of oyster restoration. Scientists will determine how common the oyster disease-causing protozoan parasite Perkinsus marinus is in oysters within Alabama and Mississippi coastal waters. They also will test a new way of growing oysters with predator cues and discover if this technique increases an oyster’s likelihood to get infected with the pathogen. Researchers will study how normally grown oysters and oysters exposed to predator cues grow and survive along the Mississippi and Alabama coasts and identify areas where the oysters survive best. Working with state agencies and local oyster farmers, scientists will share their results and offer best practices for restoring oyster populations and growing oysters on farms. Citizen scientists and high school students will be included in this research to raise their awareness of environmental issues and develop aquaculture skills.

Abstract

Although oysters are economically, culturally, and ecologically important, their populations have become a meager fraction of their historical levels. These declines have led to significant investment in oyster aquaculture and reef restoration efforts. The pathogenic protozoan Perkinsus marinus (“Dermo”), prevalent in the Gulf of Mexico, contributes to mass mortality events when temperatures are high or conditions stressful. Consequently, this disease is expected to increase in prevalence and intensity with climate change. Despite its significance, current assessments of Dermo in Alabama and Mississippi are over a decade old, hampering the ability of decision-makers to select appropriate sites for restoration and aquaculture.

To avoid consumption by predators, oysters can produce a heavier, stronger shell that adds protection and improves survival. Research demonstrates that exposing oysters to predator cues during production elicits oysters to grow stronger shells and is therefore a promising technique to produce resilient oysters for aquaculture and restoration. However, the energy used to generate the shells may come at an expense to immune function and therefore disease susceptibility. This energy reallocation could make oysters less resistant to Dermo and reduce the benefits of predator induction. This information would influence where and how oyster restoration and aquaculture should be performed. Several hatcheries in Alabama and Mississippi are interested in adopting the induction technique into their production cycle should it not impact disease susceptibility. Therefore, it is important to determine how predator cues impact oyster survival after deployment.

The purpose of this research is twofold. First, we seek to quantify Dermo throughout coastal Mississippi and Alabama. Second, we will test how predator cues affect oyster susceptibility to Dermo by triggering physiological changes in oysters. We will partner with two state agencies, three oyster farms, and a network of citizen scientists to conduct a large-scale field experiment, incorporating regions of greatest relevance to the industry. This field work will provide an up-to-date survey of Dermo prevalence in the region while simultaneously comparing Dermo intensity in predator-induced and non-induced oysters to examine potential differences in susceptibility. Our field work will be integrated with an in-depth laboratory experiment to determine how induction affects Dermo concentrations over time in an environmentally controlled setting. 

These results will describe Dermo abundance in relation to local environmental conditions and provide current Dermo prevalence data to the Regional Shellfish Seed Biosecurity Program database to guide state regulators and industry members on best biosecurity practices. Moreover, this project will evaluate the risk of disease along the coastline and the success of the oyster induction technique across a wide range of conditions. This will guide future restoration and aquaculture site selection and inform remote setting facilities both regionally and nationally in selecting techniques for maximizing their return-on-investment. By working directly with hatcheries, state agencies, and farms, technology transfer to the industry will be immediate. Furthermore, our partnerships with citizen scientists and a local high school will provide training in aquaculture techniques and awareness of environmental issues in our pursuit of Sea Grant priorities related to healthy ecosystems, sustainable fisheries, and workforce development.

Objectives

1. To quantify Perkinsus prevalence along the Mississippi and Alabama coastline and update the Regional Shellfish Seed Biosecurity Program database. 
2. To test a new oyster culturing technique and determine whether predator induced oysters have increased susceptibility to Perkinsus infection. 
3. To characterize the performance (i.e. growth and survival) of normal and induced oysters across the Mississippi - Alabama coastline and identify where performance is maximized.
4. To collaborate with state agencies and local oyster farmers to help inform stakeholders of best practices for oyster restoration and aquaculture. 
5. To involve high school students in research and improve workforce development.

Methodology

We will partner with two state agencies, three oyster farms, and a network of citizen scientists to conduct a large-scale field experiment, incorporating regions of greatest relevance to the industry. This field work will provide an up-to-date survey of Dermo prevalence in the region while simultaneously comparing Dermo intensity in predator-induced and non-induced oysters to examine potential differences in susceptibility. Predator-induced and non-induced oysters will be cultured at the Auburn University Shellfish Laboratory (AUSL) before distribution to 20 sites across the Mississippi - Alabama coastline. Oysters will be held in cages to ensure all mortality is either due to water quality or disease, Oyster survival, growth, Dermo infection presence and intensity will be check at least one month after deployment during mid-summer and again early fall when Dermo is most prevalent. Findings will be examined in concert with measurements of local water quality and land-use. 
Our field work will be integrated with an in-depth laboratory experiment to determine how induction affects Dermo concentrations over time in an environmentally controlled setting. Induced and non-induced will be raised at AUSL and placed into individual containers with sterilized artificial seawater. Half the induced and half the non-induced oysters will be injected with a mass-specific concentration of Perkinsus cells while the remaining half will be injected with sterile seawater as a control. Oysters will be checked daily for mortality while Dermo infection prevalence and intensity as well as oyster physiological condition will be examined 2-, 7- and 14- days post-injection.
 

Rationale

Oysters are an economically, culturally, and ecologically important species, but their populations have become a meager fraction of their historical levels. This has prompted heavy investment to restore populations with states spending millions on constructing remote setting facilities to breed and plant oysters. Yet, these efforts have encountered several challenges. While disease is considered a major threat to oyster aquaculture and restoration, information on its current prevalence in Mississippi and Alabama are outdated. In particular, the pathogenic protozoan Perkinsus marinus (“Dermo”) is especially common in the Gulf of Mexico and thought to be a major cause behind many mass mortality events. While this disease is expected to increase in prevalence and intensity with climate change, records of its abundance in Mississippi and Alabama are over a decade old, hampering the ability of decision-makers to select appropriate sites for restoration and aquaculture. 

Concurrently, predation pressure is extremely high in the Gulf where the vast majority of planted oysters can be lost within the first week. To avoid consumption by predators, oysters can grow a heavier, stronger shell that adds protection and improves survival. Research demonstrates that exposing oysters to predator cues during production elicits oysters to grow stronger shells and is therefore a promising technique to produce resilient oysters for aquaculture and restoration. However, the energy used to generate the shells may come at an expense to immune function and therefore disease susceptibility. This energy reallocation could make oysters less resistant to Dermo and reduce the benefits of predator induction. This information would influence where and how oyster restoration and aquaculture should be performed. Several hatcheries in Alabama and Mississippi are interested in adopting the induction technique into their production cycle should it not impact disease susceptibility. Therefore, it is important to determine how predator cues impact oyster survival after deployment.