Researchers at the University of Central Florida (UCF) are investigating the ongoing conflict between oysters and mangroves in coastal ecosystems. After nearly two decades of studying oyster restoration, Linda Walters and her team, including Katherine P. Harris and Meghan Bradburn, are focusing on how mangrove encroachment affects oyster reefs. That’s where this research is incredibly important. Over the last two to three decades, mangroves have become greatly established, tripling their distributions into regions that are home to oysters.
Mangroves have taken over the oyster reefs, increasing sediment acidity. Oyster mortality This dramatic change in ocean chemistry threatens every stage of oyster development. This grant funded multi-year study of the ecological and physiological interactions between these two important coastal species. It aims to identify strategies for balancing their impacts to benefit both marine ecosystems and coastal communities.
The Impact of Mangrove Encroachment
Mangroves have heavily encroached into oyster habitat, resulting in an interesting ecological balance that scientists are eager to unpack. Perhaps the most alarming discovery over the past few decades is that acidity levels in mangrove-dominated coastal ecosystems have increased significantly. They’ve even recorded up to 142% more protection compared to areas without mangroves. This increased acidity is highly detrimental to oyster health, causing their shells to dissolve.
In mangrove-dominated areas, oyster shells may undergo mass loss of up to 40% in just two years. People living outside of mangrove areas only suffer a loss of under 1%. This gap in basis begs the question of what’s ahead for oyster reefs. These reefs are critical to coastal environments, too—filtering out pollution and serving as habitat for thousands of marine species.
“Mangroves will naturally acidify surrounding sediment, which may not be great for oysters. Oysters, as a calcifying organism, are more vulnerable to being dissolved away in sour, acidic waters.”
As mangroves expand, scientists find themselves faced with a tough, ethical choice. Should they prune or cut down these invasive trees from new oyster reefs to protect the mollusks? Linda Walters emphasizes the need for a nuanced understanding of this complex relationship: “This is the primary question that we get: Should we now be removing mangroves from oyster reefs, including restored oyster reefs?”
The Importance of Oysters and Mangroves
Both oysters and mangroves offer key services to coastal ecosystems. Each adult oyster filters around 20 gallons of water per day, clearing up the water and creating habitat for a wide variety of other marine species. Their decline can lead to diminished food supply for birds, crabs and fishes. Even this small legislative change has the potential to make the whole ecosystem a lot more accessible.
Mangroves can protect shorelines from storm surge and erosion. Walters notes that losing oyster reefs would diminish this protective capacity: “Primarily, we’d lose water filtration capacity as well as some protection against storm surges and erosion.”
“It’s really important to understand that both of these habitat types are essential.”
Alongside their work developing new models, the research team has worked to find pragmatic solutions to gulf coastal restoration efforts. In the past academic year alone, they have grown approximately 1,700 mangroves across 35 classrooms, engaging students in restoration efforts while gaining insights into the challenges facing these vital ecosystems.
Future Directions in Coastal Research
As scientists continue to explore the connection between oysters and mangroves, they know this field is still in the early stages. Harris points out the novelty of the situation: “There is something novel about mangrove encroachment on oyster reef islands and this requires further study.”
“Live oysters are probably going to be able to have some pushback against acidification,” she explains. But, she notes, it might short-circuit their development as they sapped energy from getting bigger.
The impacts of this study go well beyond the lab and are already informing on-the-ground coastal management and restoration efforts. Walters expresses her commitment to providing actionable insights for resource managers: “We work on public lands, state and national parks, so our mission is to provide the science to the park resource managers to help them make decisions.”