What the Shuck is Happening with Summer Oyster Mortality?

This summer, we invite you to explore the stories and outcomes of our 2024-2025 Bass Connections project teams. This series features team-written profiles that showcase the discoveries, challenges and impact of teams who spent the year tackling real-world problems.

The Climate Change Impacts on Farmed and Wild Oysters team headed to the Bogue Sound along the North Carolina coast, to study how shifting environmental conditions are affecting oyster health. By tracking everything from water temperature to salinity at two coastal oyster farms, they worked to identify stressors linked to oyster mortality – and explored how smarter farming practices could help North Carolina's aquaculture industry stay resilient in a warming world.

This team was led by Betsy Albright (Environmental Sciences and Policy), Nicolas Cassar (Earth and Climate Sciences), Thomas Schultz (Marine Science and Conservation), and Juliet Wong (Marine Science and Conservation).

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By: Members of the Climate Change Impacts on Farmed and Wild Oysters team

Wild oysters have been harvested for thousands of years. Today, however, most oysters that people eat are grown on aquaculture farms.

Oyster farming has historically been widespread on the East Coast, but southern states like North Carolina have only readopted the practice within the last few decades after periods of oyster population decline.

The Duke University Marine Lab (DUML) in Beaufort, North Carolina has had an oyster farm – the Duke Aquafarm – for more than seven years. Our project represents a leading implementation of the Aquafarm as a platform in which to conduct long-term research projects. 

Over the last decade, farmers in North Carolina have frequently observed mass mortality events during which upwards of 90% of their oysters die over only a few weeks. These mortality events are especially common in the later months of the summer. However, the cause of these mortality events is yet to be conclusively determined. In our experiment, we sought to investigate if certain environmental conditions caused mortality and if certain farming decisions could help mitigate mortality risk. 

“As a marine science student, one thing that’s really great about Bass Connections is that it provides a defined link back to the marine community out of the Marine Lab ... [It was] great to have something concrete to connect with the people there.” –Molly Honecker ’25, Marine Science & Conservation

To do so, we captured continuous environmental quality and oyster biological data for an entire summer at two oyster farms. We monitored the Duke Aquafarm, which has never experienced extreme mortality, as well as a neighboring farm located at North Carolina State University’s coastal facility, the Center for Marine Sciences and Technology (CMAST), which had previously experienced mass die offs.

From May to October of 2024, we placed oysters and environmental sensors on both farms, measuring mortality every other week and growth once a month. To test the impact of different farming practices on mortality, we utilized oysters with different genetic backgrounds, stocked them into bags at different densities and flipped the bags at different frequencies. Flipping the bags helps keep them cleaner and lighter, as the side of the bag exposed to the air becomes dried out, causing any fouling organisms that have grown on it to fall off.

The environmental variables we monitored at each site included temperature, salinity, pH and dissolved oxygen, with sensors placed in an array slightly off each farm and inside oyster bags. Additional environmental variables associated with precipitation and wind were downloaded from publicly available sources. Environmental conditions can impact the growth and health of oysters, ultimately resulting in differing time to grow to market size, appearance and overall crop yield. 

After ending our experiment, the team spent the next several months digitizing, cleaning, verifying and analyzing the data. Although a mass mortality event did not occur at our farms, our data still revealed meaningful patterns.

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First, despite having originated from the same source locations and genetic strains, as well as being located in the same sound, the oysters at the Duke Aquafarm were larger and healthier than oysters at CMAST. CMAST oysters did not grow as large or as quickly as those at DUML, although their shells grew thicker. We hypothesize that this is due to intense mechanical energy created by both waves and boat wakes that the CMAST farm experiences due to its proximity to the Intracoastal Waterway.

Second, we found that pH and dissolved oxygen were more variable at DUML than at CMAST. In early August, Tropical Storm Debby made landfall in North Carolina. As a result, salinity and temperature decreased at both farms. It is speculated that Tropical Storm Debby and other storm events may have prevented a summer mortality event because they caused temperatures to decline (i.e., potential prolonged heat and/or drought events were disrupted).

We presented our findings at the 2025 World Aquaculture Society Conference, which bridges disciplines related to aquaculture from various sectors. 

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Using Wix and Streamlit, we also created an online data sharing platform and data visualization tool with digital, interactive versions of graphs to share key findings with oyster farmers, scientists and the public. To spread awareness about the impacts of climate change on aquaculture, we hope to transform this platform into a digital archive of environmental and oyster data that is updated in real time. The data visualization tool allows users to investigate the data presented on our team’s research poster at different temporal resolutions and across various data types. This will allow users to investigate their own questions using our data by zooming in on areas of particular relevance.

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In 2025-2026, our project team will continue to investigate the variables contributing to mass oyster mortality events while integrating new questions raised by the past year’s results. The experimental design for Summer 2025 includes five total sites, adding three active commercial oyster farms to the two research sites studied in 2024. We are also planning to monitor additional variables such as wave energy, water sampling and oyster body condition. We are excited to see what new insights and experiences are in store for the second year of the Climate Change Impacts on Farmed and Wild Oysters team!

“We’ve had the opportunity to see this really big research project through all the way from the initial formulation stage to now ... starting to figure out our plan for the next year.” –Sara Norton ’25, Marine Science & Conservation and Biology

Learn More

• Interested in climate research? Check out the work of this team.
• Explore current and previous Bass Connections teams.
• Learn about the project team experience through stories from students.