A field of the invasive seagrass Halophila stipulacea. The seagrass spreads quickly by fragmentation - little pieces break off, may float for several days, then potentially resettle in a new area and start growing again. JUSTIN CAMPBELL / FLORIDA INTERNATIONAL UNIVERSITY
A new invasive seagrass has been spotted off the waters of South Florida and scientists are working to see what danger it could pose for native seagrass and the plants, fish and marine animals they support.
The seagrass, called halophila stipulacea, was discovered in a marina on Key Biscayne in Biscayne Bay. This is the first time it has been identified off the coast of the continental United States. The non-native species could be a threat, depending on whether or not the newcomer will compete with and displace native seagrass species, said Justin Campbell, Florida International University marine scientist.
The problem is, scientists just don't know yet.
The invasive seagrass came from around the Red Sea and the Suez Canal area and is native to the Western Indian Ocean, Campbell said. It crossed the ocean, probably as part of boat passage from the Mediterranean, he said. It showed up in the Caribbean on the island of Granada around 2002. By 2017, it had spread to the Virgin Islands and Puerto Rico.
"And then now, very recently, it has showed up on our doorstep here in Florida," Campbell said.
The invasive species doesn't look like our native seagrass, which has long leaves and tall, grass-like canopies. The invasive species has short, tiny leaves, he said. Scientists believe it has been spreading through a process of fragmentation or asexual reproduction. The species fragments very easily, meaning that small pieces can break off, Campbell said. "Those small fragments have the capacity to float for a week, 10 days, and then potentially resettle in a new area and start growing again." It's essentially a clone of the parent fragment, he said.
Campbell, who is also an assistant professor of biological sciences at FIU's Center for Coastal Oceans Research, is the lead author of a research paper published in August on the discovery.
The concern comes from reports from the Caribbean "that this species can actually outcompete and displace native seagrasses," Campbell said. There are different anecdotal accounts, he said. On one hand, maybe the invasive seagrass is just appearing in areas where something else caused the native seagrass to disappear, and the invasive species come in afterward and colonize the area, he said. "The other case is where there is an actual interaction between native and invasive sea grasses, where the invasive seagrass will encounter a native meadow, and actually what we call outcompete it. So choke it out for space, choke it out for light and actually have a negative influence on some of these native meadows."
"It's really hard to predict what the consequences of this are going to be," said James Fourqurean, a co-author of the research paper and director of the Coastlines and Oceans Division in FIU's Institute of Environment. "This is a species that can spread incredibly rapidly. The meadows that were just discovered this summer (in the bay) are too large to have grown in a single year. So we know that it's been here for multiple years already."
The invasive seagrass will eventually spread even to the Gulf of Mexico, though not directly from Biscayne Bay, he said. "There's no biological reason that it won't grow all around the Gulf of Mexico," he said. "It'll get there. It's just a matter of time."
In the balance are the potential impacts on habitat and food for endangered species, multiple marine sea creatures that rely on native grasses as nurseries and nourishment for their young, as well as economic impacts to recreational, commercial and sport fishing industries.
Campbell said native seagrasses are "sort of like the unsung heroes of the coastal environment. They're like these underwater prairies or underwater savannahs. And they provide lots of different ecological services," he said. "So they serve as a habitat and food source for marine life. But they also help to stabilize our shorelines. They help to purify the water. They also can actually store carbon," he said. "They take carbon out of the atmosphere and store it below ground. And that's a potential mechanism for slowing down climate change."
In South Florida, there are roughly 16,000 square kilometers (about 6,177 square miles) of native seagrass meadows, Campbell said. "We have some of the most pristine and well-protected meadows in the Western Hemisphere. The value that they have to these areas, both ecologically and economically, is almost immeasurable."
Our native seagrasses are a habitat for endangered species, Fourqurean said.
"They're also habitat for a lot of the really important commercially harvested species, including spiny lobster, pink shrimp and black grouper," he said.
The sport fishing business largely targets seagrass flats, looking for bonefish, permit, tarpon and redfish, he said. They're also habitat for a lot of iconic species like smalltooth sawfish and queen conch, as well as food for manatees and sea turtles, Fourqurean said. "There are a bunch of herbivorous fish that eat it as well. And so a lot of the things that make Florida waters, Florida waters to those of us that go visit them depend on the seagrass habitats."
There are also valuable ecological services provided by seagrass that are harder to see, Fourqurean said. One is that it is a water quality regulator because it stabilizes the bottom and clarifies the water, he said. But now he believes that people are starting to think the most valuable part seagrasses play for humans is the role they play in protecting us from erosion and sediment movement in the coastal zones "because they hold the bottom down very well," he said. "And so they cut down on storm energy."
Fourqurean is also one of the lead scientists in the International Blue Carbon Working Group, which seeks to recognize and highlight the importance of coastal ecosystems like seagrass, mangroves and tidal salt marshes for their ability to capture and store significant amounts of carbon dioxide in the soil and help lessen the impact of climate change.
Campbell said that the scientists are in the very early stages of their work on the invasive seagrass and the role it plays. "It was only discovered like maybe two months ago," he said.
Right now, the strategy is to determine where else the invasive seagrass is and monitor where it's starting to interact with native grasses, he said. They also need to have discussions with federal and state agencies about management.
"And that is that is a really tricky conversation to have," Campbell said. "It's in a unique area now because it's near a national park." There also needs to be input from the Caribbean, where the invasive grass is already well-established, he said.
There have been reports where people have tried to remove it and it has not been successful because it's too costly and the plant fragments very easily, Campbell said. "And so going through the process of removing it could actually make the spread worse."
The state Department of Environmental Protection has a citizen science program where the public can report instances of marine debris, coral bleaching and invasive species. Campbell asks that if you observe instances of the invasive seagrass Halophila stipulacea, report it to the Southeast Florida Action Network at floridadep.gov/rcp/coral/content/seafan southeast-florida-action-network, or call the SEAFAN hotline at 866-770- 7335. |