Off the coast of Florida lie marigold meadows floating in the ocean; they’re trails of sargassum, a seaweed that bobs on the surface of the water. Amid those frilly ocean mats, young sea turtles grow up, learning about life in an oasis protected from predators.
In 2012, a research team scooped up 21 newly hatched green turtles and brought them to their lab. They were kept there for about three months, until their shells were about the side of salad plates. Then, the researchers fastened a non-invasive marine adhesive to the turtles’ shells (one that wouldn’t bother the turtles as they grew and moved about the ocean) and stuck them with trackers about the size of an AA battery.
“Since this was the first time any green turtle of this age/size had been tagged and satellite tracked, we used lab-reared turtles to get an initial idea of where they go, to make it easier to target areas offshore where they might be found,” said Kate Mansfield, a biologist at the University of Central Florida and director of the marine turtle research group there, in an email.
The turtles’ haven is within the Sargasso Sea, a warm, borderless water mass off the southeastern United States, named for the sargassum that occupies it. Mansfield and her team knew that the turtles have an internal compass that makes sense of Earth’s magnetic field; previous research had mimicked the field in the North Atlantic gyre, and the turtles hovered inside the lab-based ‘gyre.’ Given this, the team figured the turtles would likely stay within the real, much more massive oblong gyre that sits off the coast.
Not only did the turtles keep within the currents, they stayed within the sea that occupies the centre of the gyre, according to the new study published in the Proceedings of the Royal Academy B. Following their release in December 2012, the turtles slowly made their way out to sea. One got as high up the seaboard of New Jersey before turning back toward warmer waters. Over the next few months, though, the turtles all headed for the Sargasso Sea, something the researchers didn’t expect.
The team thinks that the water’s temperature, combined with the bounty of food sources and the sargassum’s coverage from predators make it an ideal nursery for the turtles. The behaviour would also resemble the activity of loggerhead, hawksbill, and Kemp’s ridleys, all of which hang out in the North Atlantic, and the latter two of which Mansfield has observed hanging out in sargassum in the Mexican gulf. Less is known, though, about the duration of the turtles’ stays in the region.
“The big question,” Mansfield said, “is how long these species may spend offshore in their oceanic stage.”
Mansfield’s team is now engaged in that next step; rather than launching turtles naive to the ocean into the great blue yonder, they’re picking them up from the sea and seeing where they go from there. Those turtles will not only show that next stage in the animals’ oceanic treks, but they’ll also have the benefit of not starting the first few months of their life in lab — they are wholly products of their natural environment.
Though not shell-shocking, the turtles’ trajectories from shore have shed new light on the trips these animals take to sea. I wouldn’t blame the little critters if they just continued to hang out on that sargassum. It looks relaxing.