Invasive species suffocate mangroves. But could they help these wetlands in Bradenton prosper?

From a bird's-eye view, dark lines cut across Tidy Island, leaving a trace like old scars.

A grid of mosquito ditches was carved into the 240-acre mangrove island between the 1950s and 1970s, well before it became home to 96 residents in a development of the same name. Excavating these ditches led to spoil piles, which made a hospitable environment for invasive species.

Exotic plants like Brazilian peppers, Australian pines and carrotwood can essentially invade and suffocate native species such as mangroves. The typical procedure is to cut out the intruding plants and take them away, maybe even burning them for disposal.

But is there a way to remove invasive species and supplement the environment it was once destroying? Researchers at New College of Florida are looking to find out.

Last month, the U.S. Environmental Protection Agency's Gulf of Mexico Program awarded the Sarasota college a three-year, $294,198 grant to look into two methods of invasive species disposal: killing the plant and leaving it in place, or turning it into mulch and spreading it in the wetlands.

New College assistant professors of biology Brad Oberle and Jayne Gardiner will lead a group of students in the project, with assistance from the Sarasota Bay Estuary Program and Sandra Gilchrist, biology professor and director of the Pritzker Marine Biology Research Center.

As a botanist with focuses in forests, carbon sequestration and climate change, Oberle said he would be measuring how carbon moves through the trees, fallen leaves and soil. Researchers want to see what are the effects of either killing the invasive species and leave them on site, mulching the exotic plants and keep them on land or placing the mulch in the water.

The study, said to be the first of its kind in Florida, will involve one year of observation of the current environment starting in fall 2018 and one year of monitoring after invasives are removed from the research areas in summer 2019, with one of the areas receiving the mulch treatment.

Gardiner, whose area of research includes the biology and behavior of fishes, said that if the mosquito ditches in Tidy Island are anything like similar ecosystems in the lower Tampa Bay area, they could be perfect habitats for juvenile fish like snook, redfish and spotted sea trout.

Mangrove leaves naturally fall into these mosquito ditches, creating a food source for the invertebrates that in turn feeds the young fish. Adding mulch (without seeds, of course) to these areas could supply even more food for these organisms, Gardiner said. A downside: aside from the difficulty of controlling exactly where the mulch will stay, more organic material could also "overload the system" and lead to bacterial bloom.

"Mangroves are super valuable, but they're valuable for different reasons," Oberle said. With restoring mangroves, "we don't really know if it's a win-win scenario."

He thinks that the study will show that there is a "trade-off." For instance, if invasive species are removed, it could benefit the fish but lower the carbon storage capability of the environment; if exotic species aren't removed, carbon storage increases, but it won't help the fish, he said.

Whatever does happen, the study will monitor water quality and flow, salinity, oxygen levels, carbon cycling and how fish use the habitats.

Tidy Island is "actually in fairly decent shape," Gardiner said.

The development comprises 15 percent of the entire island, according to its website, concentrated on the southern shoreline on Sarasota Bay. Its residents are for the project, some of whom are retired scientists.

The remaining acreage on the northern side makes up the largest protected mangrove habitat on the bay. The land — which consists of white, red, black and buttonwood mangroves — was deeded to the New College Foundation in 1984, and offers the perfect study location for New College researchers.

Gardiner said she hopes the results will influence how future mangrove restoration projects are conducted, by providing evidence on how these methods affect both plants and marine life. With this approach, she's looking forward to the multi-disciplinary collaboration.

"It's fun to bring a team like this together for a project like this," Gardiner said. "It's an exciting thing in science to work with people who do different things than you do."

Hannah Morse: 941-745-7055, @mannahhorse

This story was originally published April 18, 2018 at 2:26 PM with the headline "Invasive species suffocate mangroves. But could they help these wetlands in Bradenton prosper?."