Be on the lookout for mangroves marching north

Wild Ways

Those of us who live in Nassau County are very familiar with our coastal salt marshes, and many residents know the value they hold as nursery grounds for fisheries, shrimp, crabs and other species we enjoy for food and for recreation. Our climate is not tropical enough to support any of the three mangrove species in Florida, which are found in more southern coasts of Florida and have similar ecosystem values.

Until recently the dogma was that mangroves in Florida are only found as far north as Cedar Key on the Gulf Coast, and up to Ponce Inlet just south of Daytona on the east coast. If you visit either place you will see them. The species found that far north are mostly black mangroves, a type of mangrove that can return after a frost.

I always associate mangroves with my long-ago fieldwork in Southeast Asia, one of the habitats that my study animals, Asian otters, roam about in. Mangroves in Asia, though, are under dire threat due mostly to human activities. In my old study sites and in hundreds of square miles around the region, mangroves have been, and continue to be, destroyed to make way for shrimp farms. It was heartbreaking for me to go back to Malaysia last year to revisit a “protected area” there that was being denuded of mangroves, channelized and turned into a mega-shrimp farm operated by foreign interests. 

With this area denuded of mangroves, there is no nursery ground left for the fish, shrimp and crabs that form the main diet and modest income of the artisanal fisher folk who have thrived in that area for generations. Their livelihood is mostly gone, and the only thing they can do now is try to get one of the few jobs working for the shrimp farm. But at the meager wages they are paid, they cannot even afford to eat the shrimp they farm! And it is the product of these farms, full of antibiotics and artificial food, which are imported to the United States by the countless tons, at cheap prices that undermine our own struggling wild-caught shrimp industry.

Here in the United States, at least mangroves are heavily protected. On a recent visit to Cedar Key, I saw plenty of healthy mangroves in mud flats full of fishing egrets and herons.

The town itself is surrounded by mangroves, and buildings were built around them.

Similarly, at Ponce Inlet, I recently saw many acres of mangroves full of wading birds and fishermen offshore. Without federal and state protection, the situation at both places might soon resemble that of coastal Malaysia, but instead of shrimp farms we would have more homes.

It was only on my recent scenic drive back from Ponce Inlet to Fernandina along A1A that I started thinking about the distribution of mangroves in Florida. Because once I started looking closely, even north of Ponce Inlet there were mangroves. In fact, I saw them all the way up the coast north of Daytona, at Marineland, and then even north of St. Augustine at the Guana Tolomato Matanzas Reserve.

I’ve done some internet research now, and sure enough mangroves – at least on the east coast – are marching north. Landsat images collected for 28 years clearly show this range extension and expanded acreage of mangroves to the north. Apparently this is yet another result stemming from global warming and climate change. It is not correlated with warmer temperatures per se, but with fewer hard freezes that prevent mangroves from recovering from a frost.

It is a gradual process, this replacement of one ecosystem (salt marshes) with another (mangroves), but it is indeed underway. There is no consensus, or indeed much study, on the economic impact from this gradual change. Both habitats provide nursery grounds for valuable fish and shellfish species, but there are some differences in which birds, fish and other species are found where.

I wonder if this gradual change will be visible here within my lifetime. At the rate things are going, I’m thinking yes. Keep your eyes out for the first sign of a mangrove plant in the salt marsh – scientists will be interested. And I’ll be interested, too. Please let me know!

Pat Foster-Turley is a zoologist on Amelia Island. She welcomes your nature questions and observations. 

 

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