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Newly banned beach weed threatens sea turtle nesting sites

With this year’s sea turtle nesting season nearing its conclusion in Florida, many of the protected species’ newest hatchlings have completed their first big journey from their sandy nests to the water.

But a crawling plant introduced to some Florida beaches may threaten their nesting grounds, and University of Florida experts are attempting to mitigate the risk before the plant overtakes the coasts.

A closeup view of beach vitex growing on St. George Island

A closeup view of beach vitex growing on St. George Island, a barrier island bordering Apalachicola Bay, shows the woody vine and clusters of seed-filled pods. A few of its flowers can be seen in the featured image at top, which also shows its ability to overtake an area. (Photos by Deah Lieurance, UF/IFAS)

The visually attractive beach vitex, scientifically known as Vitex rotundifolia, sprawls well across the turtles’ favorite nesting site, sand dunes, and sprouts clusters of delicate purple flowers. In the United States, the plant grows natively only in Hawaii, according to the U.S. Department of Agriculture (USDA). Its invasiveness was quickly apparent when introduced to the contiguous United States, said Deah Lieurance, a UF/IFAS Extension scientist who coordinates the UF/IFAS Assessment of Non-Native Plants in Florida’s Natural Areas.

The woody vine outcompetes nearby plants and threatens coastal habitats, tendencies that prompted Lieurance to petition the Florida Department of Agricultural and Consumer Services (FDACS) to add it to the state’s noxious weed list. The plant was officially added in the latest update, which makes it now illegal to purchase the plant in Florida or move it into or within state boundaries.

“We’re just starting to see this plant pop up along our coasts,” Lieurance said. “In risk assessment, a lot of what we do is behind the problem, but this was the perfect chance to get something listed before it is everywhere.”

Beach vitex was first introduced to the southeastern United States in the aftermath of 1989’s Hurricane Hugo, with South Carolina beachfront property owners adding it to stabilize the fragile dunes and prevent erosion. As it turned out, though, not only was it a poor stabilizer, but within 10 years of introduction, it had crowded out native species and been identified as invasive in that state. More effective dune stabilizers, like sea oats and American beach grass, were among the species it readily overtook.

“It has the ability to grow along the coasts from Connecticut all the way to Texas,” Lieurance said of the growing conditions beach vitex favors. “So far, it’s mostly stayed put in Florida, but it really shows its invasiveness along the dunes.”

In addition to the appearance of beach vitex, Lieurance said the plant can be identified by crushing its leaves, which releases a spicy fragrance that she describes as mint-like. The flowers eventually give way to seed-filled fruits in mid-summer, which can survive floating to their next destination via the nearby water.

In Florida, its reach is still largely unknown. Two UF/IFAS Extension agents, one from a Gulf of Mexico coastal county and the other from a county on the Atlantic coast, have identified the plant on their shores.

Rick O’Connor, the UF/IFAS Extension Florida Sea Grant agent in Escambia County, says he and volunteer surveyors have identified beach vitex at 72 sites, which can mean anything from a 25-square-foot area to a single plant. For those sites, 80% have either been removed or are in the process of being removed, he said.

Each plant has one single, large root, and offshoots spread across the sand. Sometimes the taproot is too large to be removed mechanically, O’Connor explained, and he or another licensed herbicide applicator must treat the root. He cited Clemson University research that indicated a beach vitex plant can’t be considered eradicated until after five years of continued monitoring.

If the entire plant is not removed, UF/IFAS Extension Nassau County agent Justina Dacey said she has seen it reappear within six months.

“It’s not easy to remove,” she said. “The taproots can run pretty deep, and we try to avoid pulling up sea oats at the same time.”

Complicating matters, both Dacey and O’Connor noted, are the private properties that have beach vitex. For each site, O’Connor said he educates the owner on the plant’s invasiveness and recommends removal. At a minimum, owners are asked to remove the seeds to prevent its spread, which is a delicate process that involves double-bagging and disposal to the landfill. Without that process, nearly a million seeds can be produced per square meter annually, he said.

“Even if a plant is added to the noxious weed list, there’s nothing illegal about those areas that already have it,” O’Connor said. Lieurance notes, though, that its new noxious weed status could be used to influence local ordinances.

O’Connor also mentioned the unknown impacts beach vitex could have on coastal habitats, specifically for protected species that rely on the dunes for at least part of their life cycles. Aside from the potential to entangle nesting sea turtles or their hatchlings, ground nesting birds also make their homes on beaches statewide and there’s an endangered beach mouse on Perdido Key, off the coast of Pensacola, that could be threatened by the plant overtaking its main food sources.

“The beach mice may not eat the seeds of this plant, and if it displaces the other plants, then you’ve got a food source problem,” he explained, adding that beach vitex has been found on Perdido Key. “In some North and South Carolina areas, it’s become a monoculture – beach vitex is the only thing on the dunes. That’s what everyone’s afraid of, and we need to get control before that happens here.”

He and Dacey are both using their networks of community science volunteers to keep an eye out for this invasive plant and prevent its spread.

In Nassau County, Dacey has trained Horseshoe Crab Watch and Sea Turtle Patrol volunteers to also look for beach vitex and other invasives while scanning the beach. Although the COVID-19 pandemic canceled plans for spring data collection, Dacey says monitoring efforts will resume soon with extra safety precautions.

O’Connor is utilizing the UF/IFAS Northwest Extension district to educate Master Gardener volunteers on identifying beach vitex throughout the Panhandle. He says this effort has continued throughout the pandemic with virtual meetings.

“With something like beach vitex that’s relatively new in our area, it’s hard for people in the community to see it as a serious problem,” O’Connor said. “They understand lionfish – those are very visible. But these are just a couple of plants – is it really going to be a problem?”

He adds: “By the time you see it becoming a problem, it’s too late.”

If you come across a potential beach vitex site, UF/IFAS asks that you note its location, take a photo and notify your local UF/IFAS Extension office.

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The mission of the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) is to develop knowledge relevant to agricultural, human and natural resources and to make that knowledge available to sustain and enhance the quality of human life. With more than a dozen research facilities, 67 county Extension offices, and award-winning students and faculty in the UF College of Agricultural and Life Sciences, UF/IFAS brings science-based solutions to the state’s agricultural and natural resources industries, and all Florida residents.
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