USGS scientists look to the past to learn about the future of Florida mangroves
Florida has lost much of the mangrove forests that once bordered its coasts and estuaries to development and sea-level rise. Current rates of sea-level rise combined with increasing climate variability could accelerate the loss of mangrove-lined coastlines, according to new USGS research published in the journal Nature Communications. These findings will help resource managers understand whether mangrove-forested islands and shorelines can be maintained as the climate changes and sea levels rise and how water management may help mitigate these changes.
USGS scientists Christopher Bernhardt, James Murray, Bethany Stackhouse and Terry McCloskey collect a piston core on Bob Allen Key in Florida Bay, Everglades National Park, in April 2014. Piston cores capture about 3500 years of the sediment record. Photo: Lynn Wingard, USGS
“From previous studies, we know that the mangrove zone in South Florida shifted inland as sea level rose and estuaries covered what was previously mangrove forest during the late Holocene,” said USGS research geologist Miriam Jones, the study’s lead author. “This new research is one of the most detailed studies to pinpoint how fast the transition from mangrove forest to estuary happened during that time.”
The USGS research comes at a time when state and federal government agencies and many other partners are undertaking one of the world’s largest and most ambitious ecosystem restoration efforts: to help recover the health and natural productivity of the Greater Everglades ecosystem, which includes Florida Bay.
Mangroves provide important natural services that benefit people and wildlife. They act as buffers against storm surges and rising seas, help reduce erosion and protect coastal communities. They also serve as nesting sites for birds, act as critical habitat for endangered and threatened species and provide sheltered nursery areas for commercially valuable fish and shellfish. They are an important plant community in Florida Bay, the shallow, salty water body that lies between the Florida Keys and the state’s southern tip, mostly within the boundary of Everglades National Park.
Working on islands in Florida Bay, USGS scientists studied how environmental conditions during the mid to late Holocene — the geologic period from 5,000 years ago through the present day — affected Florida Bay’s mangroves. In this low-lying region, the border between land and sea moves over time in response to cyclical forces like rising or falling seas, or it can change rapidly due to storms.
The researchers found that starting about 3,600 years ago and ending 2,800 years ago, seas were rising at the rate of about 0.67 millimeters per year, the equivalent of about 2.6 inches every 100 years. That is about four to six times slower than today’s rate of sea-level rise. At that slower rate, mangrove shorelines rapidly changed into open water estuaries, the study found.
Scientists tied the demise of the mangroves during the late Holocene to a period of increased droughts and storms driven by changes in long-term ocean-atmosphere circulation patterns.