What's Going on with Oysters in Mississippi?

Oyster reefs within the Mississippi Sound filled in pink. The yellow triangle in the west is the approximate location of where Bonnet Carré Spillway water enters Lake Pontchartrain and flows into the Mississippi Sound in the direction of the blue arrow.

This week I thought I would talk about Mississippi oyster reefs, their challenges, and the work that I'm doing to understand their decline. Oysters, and mostly the eastern oyster Crassostrea virginica, are major seafood items along the coastal United States. The oyster industry is a major commercial industry between harvesting, aquaculture (the growing of aquatic organisms in controlled settings), and environmental maintenance in areas of oyster reefs. Oysters grow on hard substrates, so unlike my previous work in the mud, these animals live in rockier areas, though they are most often living on top of other oysters or cultch (not a misspelling of clutch) - the name given to limestone rock, crushed concrete, and oyster shell that is outplanted to serve as oyster substrate. Oysters - like other sessile animals - are quite vulnerable to changes in their environment, since they cannot escape stressors until a new spawning cycle, and only then can their larvae potentially escape the threats. In recent years, we have seen increased variation in oyster survivorship due to threats like climate change, overfishing, oyster disease, and loss of suitable habitat. While we expect survivorship to vary yearly some areas across the eastern U.S. and Gulf of Mexico have seen unprecedented oyster losses. When I was at FSU, I learned a lot about the extreme losses of suitable oyster habitat and oyster reef decimation in the Apalachicola Bay system, where harvest collapsed in 2013 and was declared a Federal fisheries disaster (leading to the development of the FSU Marine Lab's ABSI program).

The oyster reefs in the Mississippi Sound have seen similar survivorship trends to those in Apalachicola Bay. While harvest and survivorship is always variable, influenced by natural and anthropogenic stressors, reefs in the Sound were quite stable until 2005. When Hurricane Katrina made landfall in August 2005, 90% of oyster reefs in the area were damaged and oyster harvesting was closed for the next two years (Vanderkooy, 2012). Unfortunately, anthropogenic stressors picked up in the subsequent years, starting with the Deepwater Horizon oil spill in 2010 and continuing with increasingly frequent openings of the Bonnet Carré Spillway (BCS) in Louisiana between 2011 and 2020. The BCS is a human-made flood control system to prevent damage to New Orleans when Mississippi River water gets too high. When the BCS opens, it diverts Mississippi River water to Lake Pontchartrain and out into the Mississippi Sound, and brings low salinity water that tends to be colder and high in suspended solids, all of which affects local animals and plants. Because of the magnitude of oyster losses caused by a dual-opening of the BCS in 2019, oyster harvesting was closed from 2019-2024. The state is quite pleased, though, that oyster reefs recovered sufficiently to support a 2024-2025 harvest season.

As part of my postdoctoral work, I am studying the natural mortality of oysters in the Mississippi Sound to compare to years when BCS openings occur. While oysters are relatively brackish animals, thriving in estuarine systems, they cannot cope with severe freshwater environments, which occur when the BCS opens. I can use the oyster mortality from years when the BCS opens to natural mortality rates to help evaluate under what conditions the freshwater input from BCS openings become too much for oysters to handle. At the same time, I am working to evaluate how mortality within the Mississippi Sound compares to oyster mortalities along the eastern United States -- Chesapeake Bay -- and elsewhere in the Gulf of Mexico. Although my work does not seek to provide solutions to the challenges facing oysters in the Mississippi Sound, I am hoping to inform individuals responsible for managing these important resources and to support science-based policy, which is needed now more than ever. If you are interested in learning more about this work or how freshwater inflow into coasts and estuaries affects marine resources, I highly recommend attending the 2025 Coastal & Estuarine Research Federation conference in Richmond, Virginia, where I will be co-hosting a session on freshwater in coastal environments. You can read more about the conference and submit abstracts HERE by April 28th, 2025. I hope to see you there.

Vanderkooy, S. (2012). The oyster fishery of the Gulf of Mexico, United States: a regional management plan: 2012 revision. Ocean Springs, MS: Gulf States Marine Fisheries Commission. 376 pp.

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