Last week PhD student Natalia Erazo and I were fortunate to get back into the field after a long pandemic hiatus. Our mission was to collect mangrove propagules (essentially a detachable bud from which the mangrove seedling sprouts) from the Indian River Lagoon in Florida for an upcoming experiment on mangrove-microbe symbiosis. Neither of us had worked in Florida before so we teamed up with Candy Feller, an emeritus scientist with the Smithsonian Marine Station in Ft. Pierce, FL. Candy has been working on mangroves in Florida and around the world for decades and is extremely knowledgeable about the ecology of these systems. She and husband Ray Feller allowed us to tag along as they checked on a few long-term experiments and study sites up and down the coast.
For those not familiar with Florida’s Atlantic coast, the Indian River Lagoon is a network of estuaries and barrier islands that stretch from north of Cape Canaveral to south of Port St. Lucie. The barrier islands form a protected waterway that provides habitat for mangroves, manatees, and a variety of other species. The Indian River Lagoon is home to quite a few people as well, and there are some issues associated with water quality. Nutrients from septic and sewage systems are cited as a cause of high phytoplankton loads and increasingly murky water, leading to a reduction in aquatic vegetation and increased manatee mortality. Key landscape features in the Lagoon are also the result of human habitation. For example, much of the mangrove habitat in the Ft. Pierce region exists within engineered mosquito abatement areas. To reduce the number of mosquitos (currently a nuisance, but previously some did carry disease) berms were created around vast tracts of mangrove habitat. These areas were then flooded, reducing the breeding success of mosquitos because they lay eggs on wet but not flooded soil.
Unfortunately, mosquito abatement also killed the mangrove trees which, while salt tolerant and adapted to life in saturated soils, require tidal action to oxygenate the water. Modern mosquito abatement efforts (while still energy and labor intensive) take this into account and mangroves are thriving in areas that were formerly stagnant abatement ponds. This is a Good Thing for anyone who likes fish, crabs, shoreline stabilization, and any of the other services that mangroves are well known for providing.
A particularly interesting feature of the Indian River Lagoon is that it is oriented north to south at nearly the northernmost known extent of mangroves on the US Atlantic Coast. This provides an excellent opportunity to study how mangroves are responding to changing climate. It’s known that mangroves are extending their range to the north, but climate change is anything but linear, and the rise in atmospheric and sea surface temperatures are accompanied by instabilities and severe perturbations. The most notable may be freezing events caused by deep intrusions of the now infamous polar vortex. Such perturbations can have a bigger impact on landscape ecology than the background climate. Mangroves are very much a tropical species but somewhat resistant to transient freeze events (at least more so than your average Florida orange tree). How they respond physiologically to these and other stressors that they encounter in their northward progression remains to be seen.
