Glynn County’s abundant salt marshes have been key to its identity since there was a Glynn County, but numerous studies cited in the federal government’s Fourth National Climate Assessment indicate that should current trends play out — depending on intensity of warmer winter air temperature patterns — mangrove forests could move in and replace the area’s signature marshes, over a span of several decades.
Bryan Fluech, an associate marine extension director for the UGA Marine Extension and Georgia Sea Grant, has years of experience in Florida, where mangrove forests are plentiful, and here in Georgia, where salt marshes remain dominant.
“We have seen a northern migration of mangroves farther north, and I was just talking with somebody today (and they were) saying they’ve seen them in Nassau County (in Florida), and to my knowledge, there still are no established reports of mangroves taking root here in Georgia,” Fluech said. “We have seen mangrove crabs and to this point there’s no evidence they’re being detrimental, but that species is typically affiliated with mangrove roots.”
He said that ecologically, mangrove forests provide many of the same benefits as salt marshes. The FNCA specifically states they both provide “seafood, improve water quality, provide recreational opportunities, reduce erosion, support food webs, minimize flooding impacts and support high rates of carbon sequestration.”
But, considering we would be trading one foundation species for another, that opens up the question as to the degree of change that could be expected in local fisheries, and how that could impact the area economy.
“You look at shrimp and crab, which we’re known for, that marsh is particularly important for their development,” Fluech said. “What might happen if all of a sudden mangrove becomes dominant, coastal wetland, what impact might that have on their populations? Both of those species, part of their life cycle is going to depend on our estuaries here. Even in Florida, you can certainly get crabs in mangroves, but that’s not going to be their preferred habitat. So you might see some shifts on that.”
One study cited in the FNCA — “Coastal regime shifts: Rapid responses of coastal wetlands to changes in mangrove cover” — which was published in December 2016 in the journal Ecology, stated that experiments showed salt marsh plants decreased with higher mangrove cover, and wading bird abundance decreased with higher mangrove cover.
A March 2017 study, “Mangrove expansion into salt marshes alters associated faunal communities,” which was published in the journal Estuarine, Coastal and Shelf Science and was also cited in the FNCA, found creatures that swim in the water and those that live on the marine floor in salt marshes bordered by mangroves are “significantly different” between those two areas, despite similarity in salinity and water temperature.
The study also found, through, that in these border areas, crabs and fish tended to be more abundant in the mangroves.
“It’s hard to say X will happen or Y will happen, but if you look at what our traditional fisheries have been and that connection to salt marsh, it does kind of make you sit there and go, ‘Well, what shift might that have?’” Fluech said. “It could be a negative one, it could be neutral, or it could be potentially beneficial.
“But our shrimp here, they’ve evolved with our marshes, not mangroves, so that’s kind of a lingering question, when you still have such an economic impact (from shrimping), even though we’ve seen changes in our shrimp fisheries, it’s still economically important to our coastline.”