Nicholls Biology Professor Publishes Research on Coastal Vegetation

Mangroves cover a live, intertidal oyster reef in Mosquito Lagoon, Florida. [Photo by Joshua L. Breithaupt, Florida State University]
Dr. Giovanna McClenachan, assistant professor of biological sciences at Nicholls State University. [SUBMITTED]

THIBODAUX, La. — A common Gulf Coast vegetation may be shifting ecosystems because of climate change, according to a recently published study by a Nicholls State University professor. 

Dr. Giovanna McClenachan, assistant professor of biological sciences, co-authored the research published in Global Change Biology along with Dr. Linda Walters and Megan Witt of the University of Central Florida.  

Using satellite images and aerial photographs, the scientists monitored oyster reefs in Mosquito Lagoon, Florida, over the course of 74 years. They found a significant increase in mangroves on live, intertidal oyster reefs during that time period. Mangroves are small trees that grow in coastal salt or brackish – a mix of salt and freshwater – waters. 

Dr. McClenachan said this increase in mangroves happened over the course of the last 30 years and coincided with a lack of extreme freeze events brought on by climate change. An extreme freeze event varies by location but is often defined as below-freezing temperatures lasting for multiple days at levels that only occur about every decade. Most mangrove varieties cannot survive temperatures below 20-24 degrees.  

“If a lack of extreme freezes continues, we might see an ecosystem shift from oyster reef to mangroves. As a result, that could lead to a shift in the type of fish and invertebrates that each ecosystem harbors,” Dr. McClenachan said. “This could have various unintended consequences for commercial and recreational fishing, as well as storm surge protection.” 

Though the research took place in Florida, it may apply to the black mangrove population in coastal Louisiana, said Dr. McClenachan, who previously served as the science director of the Coalition to Restore Coastal Louisiana.

“While few natural oyster reefs exist in Louisiana and those that do are subtidal, this research could potentially open our eyes to other climate-driven shifts that are right under our nose but we are overlooking,” she said. 

Dr. McClenachan plans to advance her research with colleagues at Central Florida and Florida State University this spring. The next step is identifying the driving factors behind the shift in ecosystems and what that means for the coast. 

“This is the first time any research documenting an expansion of mangroves on oyster reefs in modern times has ever been published,” Dr. McClenachan said. “Now we can dive into what the shift from mangrove to oyster might mean. This could impact coastal ecosystems’ associated flora and fauna, storm surge capabilities, water filtration, carbon dynamics and other ecosystem services.”

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