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USF study: Oyster reefs threatened by changes to Florida's climate

Cold weather freezes and extremes are decreasing in Florida and may be an indicator of the state's climate changing from subtropical to tropical, researchers say.
Credit: University of South Florida

TAMPA, Fla. — Researchers with the University of South Florida say oyster reefs in Tampa Bay and along the Gulf Coast are facing a serious threat from changes to Florida's climate.

Temperatures are increasing globally, and cold weather freezes and extremes in Florida are diminishing, which is a strong indicator that the state's climate is shifting from subtropical to tropical, experts say. 

In the water, researchers say they have noticed that mangroves were overtaking most oyster reefs in Tampa Bay and threaten the lives of other animals depending on oyster reef habitats. For example, the American oystercatcher, a type of bird, is classified as threatened by the Florida Fish and Wildlife Conservation Commission due to the mangroves issue, the USF study says. 

Shallow coast waters and remnant shorelines supported typical subtropical marine habitats for centuries in Tampa Bay, such as oyster reefs, seagrass beds, mud flats and salt marshes. However, a decrease in freezes allowed mangrove islands to replace previously dominant salt marsh vegetation and now have taken over oyster reef habitats that existed for centuries, researchers say. 

“Rapid global change is now a constant, but the extent to which ecosystems will change and what exactly the future will look like in a warmer world is still unclear,” Stephen Hesterberg, lead author of the USF study, said. “Our research gives a glimpse of what our subtropical estuaries might look like as they become increasingly 'tropical' with climate change.”  

The research team at USF says they found that 83% of tracked oyster reefs in Tampa Bay were fully converted to mangrove islands based on aerial images from 1938 to 2020. The rate of change has reportedly increased throughout the 20th century and after 1986, the Bay has seen a dramatic decrease in freezes, which is a factor that would typically get rid of mangroves naturally.

“As we change our climate, we see evidence of tropicalization – areas that once had temperate types of organisms and environments are becoming more tropical in nature,” Susan Bell, professor of integrative biology at the university, explained.  

Bell also said that while the transition to mangrove islands is advanced to the Tampa Bay estuary and estuaries in the southern region of Florida, the ecosystem manager in northern coastal areas of the state will most likely face tropicalization within decades. 

“The outcome from this study poses an interesting predicament for coastal managers, as both oyster reefs and mangrove habitats are considered important foundation species in estuaries,” she said.

Although mangroves provide benefits such as habitat for birds, certain ecosystems function specifically for oyster reefs as they improve water quality and coastal protection by reducing the impact of waves, researchers say. Oyster reefs can potentially be diminished or lost altogether as more reefs transition to mangrove islands and the loss of the oyster reefs' habitats will directly threaten reef-dependent species and wild oyster fisheries, the study says. 

"Although tropicalization will make it increasingly difficult to maintain oyster reefs, human intervention through reef restoration or active removal of mangrove seedlings could slow or prevent homogenization of subtropical landscapes – allowing both oyster reefs and mangrove tidal wetlands to co-exist," according to the study. 

Experts say they plan to continue studying the effects of the habitat transition on shellfisheries and how to develop an oyster reef restoration that will expand Tampa Bay's ecosystem lifespan or avoid mangrove conversion altogether.

To view the full study, click here.

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