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Sea Turtles Swim Against the Darwin Current

Was there ever a more incongruous animal to imagine being a swimming champion? And yet there they go, swimming long distance routes with unerring navigational skill. We learned in Living Waters how they climb out of their sand nests as hatchlings, knowing instantly which way to go toward the ocean. Then they swim straight through sometimes murky ocean water for hundreds or thousands of miles, navigating by the earth’s magnetic field. Up to three decades later, the turtles return to the same beach where they were born, ready to give birth to a new generation.

Additional findings about sea turtles have come to light recently, adding to these remarkable animals’ resumè of design features.

Multi-Functional Flippers

The flippers of sea turtles have to work well in the water as paddles and on sand as legs. The race of the hatchlings on the beach is one of the cutest episodes in Living Waters. The young turtles come well equipped for getting quickly across soft sand — so well equipped, in fact, that engineers have been inspired to imitate their flippers for robots that need to cross soft materials (see Georgia Tech’s video below). When the hatchlings reach the water, the flippers instantly become swimming paddles. They will function as paddles for many years until the adults climb back onto the beach, where they will instantly know how to use their legs again for crossing soft sand, and then as digging tools for their nests.

Another function of the sea turtles’ limbs was recently reported in Science Daily: “Sea turtles use flippers to manipulate food.” Researchers from the Monterey Bay Aquarium were surprised to watch the turtles swipe at jellyfish, then hold them in their “paws” and “lick their fingers” while feeding. A loggerhead was seen “rolling a scallop on the seafloor and a hawksbill pushing against a reef for leverage to rip an anemone loose.” Such behaviors have been witnessed in marine mammals like the walrus and the manatee, but never before in sea turtles. Nature mentioned this in its research highlights and posted a picture of a sea turtle gripping a jellyfish.

How could this skill have originated? The researchers needed to find an “evolutionary perspective” in which to place this behavior, so they invented one.

Sea turtles don’t have a developed frontal cortex, independent articulating digits or any social learning,” says Van Houtan, Director of Science at Monterey Bay Aquarium. “And yet here we have them ‘licking their fingers’ just like a kid who does have all those tools.It shows an important aspect of evolution — that opportunities can shape adaptations.

Since sea turtles are among the first tetrapods to display these behaviors in the evolutionary timeline, “this type of exaptation of flippers may have been occurring 70 million years earlier than previously thought,” the researchers speculate. “Exaptation,” a concept coined by Stephen Jay Gould, means “traits that were adapted for one evolutionary function, but were later co-opted (but not selected) to serve a different role.” Their paper in PeerJ puts evolution right up front: “Limb-use by foraging marine turtles, an evolutionary perspective.” Their scientific logic appears to follow two deductions: (1) Evolution is a fact, therefore this phenomenon evolved (even if earlier than we thought), and (2) Opportunity shapes adaptation, so “These behaviors may also be remnant of ancestral forelimb-use that have been maintained due to a semi-aquatic life history.” The paper is saturated with evolutionspeak, resorting to the hypotheses of exaptation (per Gould) and of convergent evolution. Well, if opportunities can shape adaptations, we should see human mermaids by now, shouldn’t we?

No Sexism in Sea Turtles

If you thought only the females had to go to the effort of swimming all the way back and climbing up the beach to breed, there’s a new paradigm about sea turtles that is more egalitarian. A new study at the University of Barcelona “breaks with the classical view on the breeding behaviour of the loggerhead turtle,” reports Science Daily, finding that “Male loggerhead turtles also go back to their nesting beaches to breed.” This was missed before because there are fewer nuclear genetic markers to study in males. Also, the sex of a hatchling is determined by the temperature of the egg: warmer eggs tend to produce more females. The paper in Marine Ecology Progress Series shows that there’s still a lot to learn about these amazing seafaring animals.

When the Shark Bites

A beautiful 3-D color model of a green sea turtle was developed the University of Massachusetts at Amherst. You can view it in motion here, zoom in, and rotate it in any direction. Turn it around from the default side, though, and you will see this one lost a limb to a hungry shark. It’s the latest in the UMass Digital Life Library, a project to develop full-color 3D models of organisms for study. The interdisciplinary effort includes biologists, artists and photographers. An embedded video shows how they make their models, and why. “Sea turtles are going to be our next frontier,” the narrator says, explaining that all seven species face numerous threats. Another speaks of “their beauty, and their fragility” in the animal world. This sounds like a good Darwin-free project to help biologists, educators and nature lovers get close to amazing creatures from habitats not everyone can reach.

Hidden Habitat

A hideout for sea turtles was discovered in the middle of the Indian Ocean. Researchers from Swansea University followed green sea turtles equipped with logging devices, and found extensive “seagrass meadows” where they congregate, reports Phys.org. These pristine meadows, 29 meters under the surface, provide habitat for the sea turtles, which forage on seagrass, as well as fish and other species of animals. The turtles were tracked migrating to the “Great Chagos Bank, the world’s largest contiguous atoll structure in the Western Indian Ocean.” The researchers think that other large submerged banks may be found in the world’s oceans, suggesting that “deep-water seagrass may be far more abundant than previously suspected.”

Threatened and Prospering Sea Turtles

Conservation efforts are having some success. Phys.org reported that nests of olive ridley sea turtles hatched in Mumbai, India after being missing for two decades. Their habitat had been damaged by “thousands of tonnes of rubbish” on one beach that volunteers have been cleaning up for the last few years.

Olive ridley turtles are known to navigate thousands of miles of open ocean to reach beaches, where they come ashore under the cover of darknessto dig shallow pits with their flippers where they deposit dozens of eggs.

The project appears to be working; at least some have their “flippers crossed” that the threatened species is making a comeback to the restored beach. Some 90 to 95 hatchlings were observed. The return of these turtles appears to be making many of the local people happy, and may encourage more cleanups of Mumbai’s notoriously dirty beaches. See the article for photos of these medium-sized sea turtles.

On the other side of the globe, Hawksbill turtles are enjoying a paradise in Nicaragua, reports Phys.org in another news item. Flora and Fauna International (FFI) has been running a campaign to educate locals not to eat turtle eggs, which encourages poachers. The project also has a positive side:

FFI is reducing poaching of sea turtles and their eggs by turning poachers into turtle protectors.Having identified priority nesting beaches, FFI has been working with local communities to provide education and sustainable livelihood opportunities. For example, economic incentives have led to many local people choosing to patrol nesting beaches and protect sea turtles and their eggs instead of poaching.

These efforts appear very successful, but since the sea turtles can live for many years, it will take a while to accurately assess the impact. Nevertheless, the good work in this “land of lakes and volcanoes” shows that conservation efforts can work when the locals get involved. We hope so; we wouldn’t want to lose another showpiece in the hall of intelligently designed animals.

Photo: An olive ridley sea turtle at the Long Beach Aquarium, Long Beach, CA.