On a thin stretch of beach near the Crandon Marina on Key Biscayne, Justin Campbell scans the water for the latest threat to Florida’s vanishing seagrass meadows: a new exotic seagrass that has hitchhiked its way from the distant Indian Ocean.
“It was here for several years before somebody found it,” he said. “So it is almost like looking for a needle in a haystack.”
That's u ntil early August, when an alert contractor doing work at the marina spotted a thick patch of the weedy grass — halophila stipulaceas — growing between two slips.
Within a week, Campbell, a seagrass ecologist at Florida International University, and a colleague were at the marina on paddleboards, searching for the grass to confirm the finding. Fearful that the grass may have spread from the busy boat basin and into Biscayne Bay, where miles of seagrass meadows are already battling pollution, busy boat traffic and increasingly powerful hurricanes, they started scouring the surrounding sea floor.
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What they found confirmed Campbell’s worst fear.
“If you look far in the distance by those mangrove trees, very close to the edge,” Campbell said, pointing toward an island that forms one side of the cut leading deeper into Biscayne Bay, “that's where we stumbled across some additional patches. And so it is now actually growing outside of the m arina.”
Campbell and other scientists’ worry is that this grass, like other exotic species that have made their way to the Sunshine S tate, will thrive and smother native grass. In the Caribbean, the grass has spread rapidly in dense patches and appears to tolerate a greater range of temperatures and salinity. It can also grow in both deep and shallow waters.
And if it's at Crandon, inching its way to popular flats that draw both boaters and sea life including sea turtles, lobster, snapper, grouper and bonefish, it may already be lurking, undiscovered, at other marinas around Florida.
If it does spread in Florida, it’s not clear whether Florida wildlife will like this new grass. The shorter, weedier grass, sometimes called Mediterranean seagrass, may also not provide the same services as Florida seven seagrasses, including buffering the coast against powerful storm surge like the flooding Helene unleashed on the Gulf Coast; sucking up huge amounts of planet-warming carbon; and holding down the sandy bottom to provide gin clear waters that once defined Southeast Florida.
The hit would be a double whammy for the region, with reefs, where fish rely on nearby seagrass meadows, also struggling as oceans increasingly warm. A summer heat wave last year bleached nearly all the reefs in the Florida Keys.
“We just can't predict how those things that we value are going to change because of this new species,” said Jim Fourqurean, an FIU professor who has been studying seagrass in Florida since the 1980s.
The invasive grass first made its way from the Indian Ocean to the Mediterranean Sea after the Suez Canal was dredged in the late 1860s, then spread gradually west across the Mediterranean to the southern coasts of Italy, Tunisia and Libya. Scientists believe it then hitchhiked a ride on yachts or sailboats — yanked up by anchors and kept alive in damp anchor holds — across the North Atlantic Ocean to the Caribbean, where it was first spotted in the early 2000s.
“We've been watching this since 2005. We've been waiting,” Fourqurean said. “And to me , it’s been a big surprise that it took this long.”
Unlike the Mediterranean, the seagrass spread quickly and in dense patches across the turquoise Caribbean. Fourqurean witnessed it first hand earlier this year when he visited Grenada, where the seagrass was first reported in 2002.
“All of the seagrass meadows that I could see as I was moving around in a small boat were all this invasive species,” he said. “I've worked on this species in the Indian Ocean and in the Arabian Gulf and in the Red Sea, and I’ve never seen it in its native range nearly as dense as we're seeing it in the Caribbean. And in that one patch in Crandon Marina, it's really, really dense. "
If it spreads out into Biscayne and around South Florida, he worries the scale of the damage could surpass the Caribbean.
“We have so much seagrass here compared to many places in the Caribbean that it has the potential for having a much larger aerial effect impacting much larger areas here in South Florida,” he said.
There’s also a lot more room to grow, where native grasses have died. Parts of Biscayne Bay have lost between about 90% to 70% of native seagrass cover, triggering a shift that scientists say can dramatically change the bay if not reversed. Around the coast, the story is the same. Since the start of the 20th century, Florida has lost nearly 40 % of its seagrasses.
“People actually go out and they dig seagrass up,” Fourqurean said. “People don’t like it off their beaches. We dredge harbors. We make water deeper. But those direct removals of seagrass are really small compared to the indirect impacts that humans have. "
Those indirect impacts include increasing pollution from leaky septic, sewer lines and stormwater run-off made worse by increased flooding from climate change.
“So humans are not very good for seagrass, but seagrass is great for humans,” he said.
Worldwide, seagrass is considered among the most efficient at storing carbon: while they make up just a tenth of the planet’s oceans, they store 18% of its carbon, according to a 2020 United Nations assessment.
In addition to being spread by boat, said Fourqurean, it’s possible the seagrass is being spread by sargassum. It produces prodigious amounts of small seeds that can easily spread. A colleague in Puerto Rico reported a mat obliterating a native seagrass meadow.
“A big sargassum mat came into the bay, went up into the mangroves and was stuck there,” he recalled. “I t persisted for months and settled to the ground and killed all the seagrass that was underneath it. And the next year he went back and that entire was this invasive seagrass species.”
But the results have not been the same Caribbean-wide, he said.
“There are places where experiments have shown that if you introduce this new species into native seagrasses, it can outcompete our native seagrasses,” he said. “And there have been other studies that have suggested that that's not really what's going on. Really, it's just moving into space where our native seagrasses used to be because they're much more susceptible to decreases in water clarity.”
That could actually help the native grasses here that grow in shallow water and struggle when too much sediment gets churned up by ship traffic or waves.
“If the native species can then compete with it and use it as a foothold to then grow up, maybe it could be a good thing. We just don't know,” he said.
Whichever it is, Fourqurean and Campbell say they need to figure out fast to determine a management plan.
“Unfortunately, my suspicion is that if it's here at Crandon Marina, it's likely over at the other marinas as well,” Campbell said. “So I think the first step is to try and understand where it actually is.”
To do that, he’s organizing surveys and asking the public and boaters — and in particular fishing guides on the flats who read seagrass like tea leaves — to be on the lookout. He’s hoping to get fliers with pictures posted at marinas. But he suspects it won’t be easy to find, more like a needle in a haystack.
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