INVASIVE APPLE SNAILS IN YOUR BACKYARD, WATERWAYS? UF/ IFAS STUDY DIVES INTO THEIR THREAT TO FLORIDA’S WETLANDS

By Lourdes Mederos

Florida is home to roughly 20% of all wetlands in the United States. In the last decade, apple snails have received attention as a potential threat to Florida’s wetlands.

In a newly published study, University of Florida researchers at the Institute of Food and Agricultural Sciences (UF/IFAS) provide the first look at the potential environmental impacts of one of three invasive apple snail species on Florida’s wetlands. The paper’s findings show how the invasion of Pomacea maculata – commonly called the island apple snail or giant apple snail – and land management combine to affect multiple ecosystem functions and services in Florida’s wetlands.

“We learned the apple snail invasion can greatly alter wetland ecosystem functions, particularly plant communities and nutrient cycling,” said Jiangxiao Qiu, assistant professor of landscape ecology at the UF/IFAS Fort Lauderdale Research and Education Center and School of Forest, Fisheries, and Geomatics Sciences, and one of the study’s authors. “All these influences can translate to impacts on ecosystem services, which are the ecological benefits to humans, such as plant productivity, water quality, habitat maintenance and landscape aesthetic values of wetlands.”

The study’s authors hope the findings will give ecologists, natural resource managers, invasion science researchers and wetland scientists globally needed information to develop tailored actions that will mitigate apple snail impacts and conserve wetland ecosystems.

“Invasive apple snails exert significant destructive impacts on agricultural wetlands serving as rice farms in Southeast Asia and the southeastern United States,” Qiu said. “In Florida, while rice farms are not dominant agricultural land uses, the understudied invasive apple snails are abundant, and they can exert impacts on natural and semi-natural wetlands.”

Florida has one native type of apple snail and three nonnative species, all of which can easily overpopulate areas by outcompeting native species. They destroy aquatic vegetation, damage agriculture and adjacent communities, and can impact human health.

“For the research community, we showed how complex and varied apple snail impacts can be for critical ecosystem functions in different wetland types,” said Chase O’Neil, a biologist on the team and lead author of the study. “This work has broad-reaching implications for other ecosystems worldwide where apple snails have invaded natural and agricultural wetlands because it can help develop management strategies.”

In the study, researchers measured how wetlands changed as a result of an apple snail invasion.

“By using a holistic experimental approach and measuring a range of wetland responses -- including vegetation, soil, water variables and functions -- we were able to understand the overall impact of the species invasion on ecosystems,” said Qiu.

The team conducted a 14-week experiment known as a mesocosm. The experimental system, designed and built by Qiu, allowed the team to examine the natural environment under controlled conditions at the Archbold Biological Station’s Buck Island Ranch. This working beef-cattle operation and research laboratory in Highlands County has an apple-snail invasion. The site contains over 600 wetlands interspersed within more than 10,300 acres of grasslands.

“This is a comprehensive study where we focused on several understudied areas in apple snail research simultaneously,” said O’Neil. “We looked at how invasive snails affect the ecosystem as a whole and how it functions, which was obviously harder to capture but in many ways is lacking from other work and is extremely valuable when looking at invasive species’ widespread impact.”

Researchers used white trash cans to hold soil, water, plants and apple snails collected from the site to create a wetland environment mimicking the field site’s conditions. The team divided experiments into two invasion treatments, one containing apple snails and another devoid of apple snails. They created two additional land management treatments, one characteristic of intensively managed wetlands and the other semi-natural wetlands.

They collected snail, soil, water and plant measurements. Scientists then compared how the presence of snails altered plant, soil and water responses compared to treatments without snails and how these differed in two types of wetlands.

“Overall, we found that invasive snails substantially decreased aboveground biomass and vegetation cover and exhibited preferential feeding on wetland plant species,” said Qiu. “Snails also increased water nutrients such as carbon, nitrogen, phosphorous and dissolved solids.”

Wetlands come in many forms, including fresh and saltwater marshes, wet prairies, cypress domes, steep heads, mangrove swamps and more. They provide a web of vital functions, including filtering impurities from water, storing water to reduce flooding, storing carbon and providing ideal habitats for many plants and wildlife species, including birds, fish and reptiles.

Apple snails can grow up to six inches high and are found in freshwater lakes, rivers, streams, ponds and ditches throughout Florida. Where they’re in abundance, they have crossed into wetlands.

While they spend most of their lives under the water, they lay their eggs above the water line. It is no longer unusual for residents to come across bright pink egg clusters on vegetation and other hard surfaces like pilings, culverts, bridges and coastal seawalls. Each cluster contains between 500 and 700 eggs.

The species was first introduced in Florida through the aquarium trade in 1989 in Palm Beach County and has since become established throughout most of the state. There are apple snails from Miami-Dade County to as far northeast as Nassau County, and as far west as Okaloosa County.

The study is available in the March 2023 journal Science of the Total Environment.