Since crawling out of its nest on a moonlit night and making its way to the sea, a green baby turtle disappears at sea for years before returning to shore. Until recently, scientists assumed that the turtles swam in the open ocean’s main currents. However, recent evidence indicates that the centre of such spinning waters serves as a previously unnoticed turtle nursery, thanks to the use of satellite tags to detect young green turtles for the first time.
“The gyre functions like a playpen’s walls, and we also need to weigh that into our management of the North Atlantic species,” says Katherine Mansfield, a turtle biologist at the University of Central Florida. The thesis of the latter was published today in the journal Biological Sciences.
Like most other marine turtles, green turtles spend their growing years in the open ocean before returning to coastal waters as adults. Researchers refer to this period at sea as the “missing years,” so we don’t know where the young turtles go or how long they’re gone.
According to Mansfield, the majority of what we knew came from “opportunistic sightings of these little baby turtles in the open ocean.” Baby green turtles have been seen in the Gulf Stream, a fast-moving torrent with warm water that winds its way up the US East Coast, as well as in the Atlantic currents.
As a result, the established theory was that the baby turtles mainly went with the tide as they circled the North Atlantic, following large ocean currents.
Attaching solar-powered trackers to young turtles with six-inch-long shells is a significant obstacle. “The bony plates of their shell, like the bony plates of baby skulls, haven’t completely fused together at that age,” Mansfield explains. If the researchers used a strong epoxy to mount the trackers, the turtles would deform as they expanded.
Instead, they tried lightweight glues, but the shells, which are made of keratin, flaked off. It’s the same stuff that goes into human fingernails, which made them think of something else. Mansfield recalls, “Jeanette [Wyneken, a co-author] and I sort of looked at each other.” “She called her manicurist and said, ‘What would you do if your nails were peeling?'”
The manicurist suggested an acrylic base coat. Turtles like loggerheads, Kemp’s Ridleys, and hawksbills thrive in this setting. ” green turtles, on the other hand, are a different story,” Mansfield says. “We spoke to a dentist and used the same bonding adhesive that dentists used for crowns,” says the author. Finally, we went to a nearby hardware store and purchased a variety of products that did not include the word “carcinogen.”
The tracker was held in place for three months before eventually dropping off as the turtle evolved, thanks to a unique marine adhesive.
When the researchers eventually had a chance to watch their group of 21 tagged turtles swim, they discovered that while all of them rode the Gulf Stream north, 14 of them ended up diving into the Sargasso Sea.
There are no land limits in the Sargasso Sea, which encompasses a two-million-square-mile area approximately covering Bermuda. Instead, the large north Atlantic currents encircle it. The water within is incredible, and extensive mats of brown sargassum seaweed accumulate on the surface, earning the area its name.
The open ocean, according to biologists, has fewer fish than coastal seas, making it a more enticing sanctuary. Young sea turtles of all sizes congregate around the sargassum mats, which provide a haven for a variety of life in the otherwise lifeless open ocean.
Tess Mackey, program manager for the Sargasso Sea Commission, a nonbinding environmental partnership between ten countries bordering the waterway, describes it as “the golden floating rainforest of the Atlantic.” “Seeing the small crabs, shrimp, and fish that live in there is like a scavenger hunt when you look at a snapshot of a sargassum mat.”
The yearly turtle hatch coincides with the seasonal migration of sargassum across Atlantic currents, though it’s unclear whether the two are related.
“It makes sense that turtles will interact with sargassum because it offers them some protection,” Mansfield explains. “A shark, dolphinfish, or mahi mahi will be swimming under those mats if you have them. The turtles have a lot of camouflage and fit in well with the sargassum.”
The Sargasso Sea is home to a variety of endangered species, including green turtles. While the exact act has never been registered, both American and critically endangered European eels migrate to the region to spawn. Other trout, both commercially essential species and those exclusive to the Sargasso Sea live in the mats as well.
The sargassum frogfish, Mackey’s favourite fish, has adapted fins that allow it to crawl around in the sargassum.
However, similar to the Pacific Garbage Patch, the sea absorbs plastic from the local currents. “Marine life, such as turtles that shelter and feed in sargassum mats, may get trapped in it, or even eat it,” says Mackey.
The Commission is planning to conduct a large-scale evaluation of the Sargasso Sea ecosystem’s importance. “Having new evidence regarding green turtles on why the Sargasso Sea is vitally important for marine ecology, in general, is particularly beneficial for us,” Mackey says.
So far, it seems the North American green turtles are the only ones who do this—their South American cousins don’t have a close nursery. “Because our sampling sizes are limited, it’s costly to tag these tiny turtles,” Mansfield explains. “Really, what it’s telling us is that we need to dig at this more closely and eventually place more tags on turtles, to actually get to the bottom of these discrepancies, to see if the species have a desired destination.”