More Than a Tasty Meal: Mussels May Help Save Salt Marshes

Jamaica Bay, nestled in the southwestern corner of Long Island, contains coastal wetlands known as salt marshes. These marshes are a source of shelter and food for plants and animals, and protect coastlines from erosion. Unfortunately, says Graduate Center Ph.D. student Jennifer Zhu (Biology), 50% of salt marshes worldwide have disappeared. To help restore them, scientists like Zhu first need to understand the interplay between the plants, animals, nutrients, and microbes that live there. Zhu and colleagues observed plots in the marshes in Jamaica Bay to see what ecological role Atlantic ribbed mussels play, and how the mussels might help ecologists bring the salt marshes back.

The Graduate Center spoke to Zhu about what she found.
 
The Graduate Center: What were the main findings of this study?

Zhu: Ribbed mussels likely enhanced denitrification, the process of removing nitrogen from the system and returning it back into the atmosphere. The waste they produce provides carbon and anaerobic conditions that microbes in the sediment need to perform denitrification.  
 
GC: Why is it important to remove nitrogen from salt marshes? Don't plants need nitrogen to grow?

Zhu: It is true that nitrogen is vital to plant growth. Excess nitrogen, however, can overstimulate plant growth, which can lead to a whole cascade of problems. Excess nutrients can allow harmful algae or other species to grow rapidly and block sunlight from underwater plants while also consuming lots of oxygen. When these plants die after taking up all the nutrients, they coat the bottom and take up more oxygen as they decompose. All this can impact plants and other salt marsh organisms that depend on oxygen. In salt marshes in the Northeastern Atlantic region of the United States, for example, large inputs of anthropogenic nitrogen such as fertilizer have reduced the organic, or living, portions of marsh sediment and decreased sediment stability. This can lead to erosion, which eventually may lead to salt marsh die-offs.
 
GC: How did you get interested in this field of research?

Zhu: During my undergraduate studies at Cornell University, I did research on the eastern oyster and got hooked on working with oysters, because of all the amazing ecosystem services they provide. I then went on to pursue a doctoral degree to continue doing research on bivalves and to understand how they impact and interact with the environment around them. Given that the eastern oyster is native to New York waters and a New York native myself, it made even more sense to work on these bivalves in my hometown. Although I have transitioned to working with a different bivalve, the ribbed mussel, for my dissertation research, I still occasionally do research on the eastern oyster with collaborators at Governors Island.
 
GC: In light of these findings, what kind of restoration projects would you propose?
 

Zhu: Current salt marsh restoration projects focus on elevating the marsh by adding sediment and planting vegetation. While these efforts have been successful, restored marshes take multiple years to function and provide services like natural marshes. I think this can be improved by including other species in restoration planning. Ribbed mussels may be a valuable addition for salt marsh restoration projects in nutrient-polluted estuaries since they increase the ecosystem service of nitrogen removal. This is especially important for New York as the Hudson River Estuary is one of the most nitrogen-loaded estuaries in the world.
 
GC: Where will your research take you from here?

Zhu: Species interactions may be especially important for restoration programs where community composition may change over time. This may be especially true when foundational species like marsh vegetation and ribbed mussels are restored to an area as part of management activities. This past summer, I conducted an experiment that considered how the removal of nutrients from the water and the production of waste by mussels changes in the presence of predators like blue crab and Atlantic oyster drill. Since we hope for predators to return to restored marshes, we need to consider how their presence might impact the services mussels provide. All of these studies will provide insight to help guide management activities and predict the types of services restored communities will provide.