Barnacles growing on airplane wreckage washed up on the island of Réunion after the disappearance of Malaysian Airlines Flight 370 have led scientists to promising new models for reconstructing the drift paths of ocean debris—and could someday help solve the great aviation mystery itself, researchers say.
The new temperature and chemistry tools, published today in the American Geophysical Union journal AGU Advances, are among the most precise yet for using shell chemistry to retrace unknown paths of crash debris, ocean plastics, dead bodies, and other flotsam carrying Lepas anatifera, known as goose, gooseneck, or stalked barnacles.
“The chemistry of barnacle shell layers is like a forensic recorder for drifting debris,” says marine ecologist Gregory Herbert at the University of South Florida, who began working on the MH 370 mystery in the summer of 2015 after seeing news accounts of a flaperon from the missing plane washed up on a Réunion beach, encrusted with barnacles.
In the eight years since, Herbert built an international team to develop methods for tracking the ocean temperatures the barnacles traveled through and statistical formulas that could, in theory, “turn that temperature history into a drift pathway that leads back to the crash,” he says.
Australian senior government oceanographer David Griffin, who has helped search for the missing jetliner since it vanished over the Indian Ocean in March 2014 with 239 passengers and crew members onboard, called the research “an important step towards possibly satisfying Malaysia’s requirement for ‘credible new evidence’ to restart the search.”
“We knew there were clues encrypted in the shells of the barnacles, but the problem was that no one really knew how to decode them,” says Griffin, who was not involved in the research. “That’s what this group has done. They’ve given us the methods to decode the data that’s there—stored in barnacle shells.”
Hitchhikers of the sea
Living throughout the world’s temperate and tropical seas, stalked barnacles begin life as free-swimming larvae that ride ocean currents until they settle, often en masse, on driftwood, a ship’s hull, or other floating objects. Lepas cement themselves at the base of their soft stalk, which secretes one of nature’s most powerful adhesives. They use calcium carbonate and other minerals from the surrounding seawater to build their wing-shaped shells layer by layer as they grow.
Each new layer has slightly different chemical markers, vestiges of temperature, oxygen ratios, and other conditions in the water where it was built. The science of reading those layers is called sclerochronology, the shell equivalent of tree-ring science.
“Imagine a shell like a thick book, where the animal has added one page after another as it grows,” says lead author Nasser Al-Qattan, a geochemistry professor at Kuwait University. Deciphering the chemical composition of each individual page—each thin, calcite layer—gives scientists a diary of the seawater through which the animal journeyed as it built its shell.
Al-Qattan was working on his PhD in Herbert’s Tampa marine science lab analyzing oxygen isotopes in mollusk shells when the flaperon’s discovery made news around the world. Photographs and video footage showed several generations of stalked barnacles anchored to the wing piece, a retractable surface that helps control take-off and landing. The size of the largest barnacles suggested to Herbert that they could have been growing for more than a year—meaning they could have hitched a ride close to the time the jetliner vanished in March 2014.
Knowing precise sea-surface temperatures and times the barnacles drifted on the flaperon could narrow the search area by an order of magnitude. Oceanographers have temperature histories from satellite-tracked drift buoys throughout the world’s oceans—and temperatures change distinctly along the search corridor known as the “7th arc” where the plane is believed to have run out of fuel.
A buzz of science news stories about the barnacles followed the flaperon’s discovery, speculating the hitchhikers would soon help narrow the search area. Griffin says the investigative team hoped so, too. But barnacle sclerochronology is an exceedingly esoteric science. And French authorities, who oversee Réunion as a territory, limited access to the flaperon and its crustacean clues.
The French released two science reports on the barnacles within a year of the flaperon’s discovery. While they were not definitive, they laid a path for longer-term research, Herbert says. Marine scientist Joseph Poupin’s expert report established the species, size range, and their growth curve, confirming larger, older barnacles on the flaperon that could have colonized close to the crash date. In an unpublished report, researchers Dominique Blamart and Franck Bassinot analyzed isotopes from some of the actual barnacles, which gave Herbert and Al-Qattan data to model part of the flaperon’s drift.
Herbert reached out to the Lepas expert Anne Marie Power at the University of Galway in Ireland, who signed on to raise live L. anatifera in aquaria to establish shell chemistry for different temperatures. Those data helped the team develop an equation that can glean sea-surface temperature records from a mystery barnacle.
The scientists conclude they can track a barnacle’s water-temperature history within 0.1 degrees Celsius, the precision Griffin says oceanographers need to narrow the search area. The methods available in the wake of the flaperon’s discovery were accurate to only about 2 degrees Celsius, which Griffin says the investigative team found too uncertain.
The research, which blends the zoology and shell geochemistry with ocean drift modeling and geospatial statistics, still has a way to go before scientists can mark an “X” on a map of the Indian Ocean. The team was able to model only the final leg of the drift path based on the smallest barnacles that had colonized the flaperon. Those youngest specimens, from the Blamart and Bassinot report, are still the only ones that have been made publicly available to scientists by French authorities. In theory, Herbert says, deploying the same methodology to the oldest, largest barnacles seen on the flaperon—those that may have hitched a ride closer to the time of the crash—could model their complete journey.
The disappearance of MH 370 remains a confounding mystery despite the multi-nation, $200 million search of 46,300 square miles (120,000 square kilometers) of remote Indian Ocean, called off in 2017, three years after the crash. The Australian government’s 429-page report on the search calls it “almost inconceivable and certainly societally unacceptable in the modern aviation era with 10 million passengers boarding commercial aircraft every day, for a large commercial aircraft to be missing and for the world not to know with certainty what became of the aircraft and those on board.”
The Malaysian government has said it will not restart another search mission without evidence that is both “new” and “credible.”
“The case has gone cold, and at this point it’s very hard to actually find new evidence,” says Griffin. Whether the new barnacle methodology will meet that standard, he says, “I think we will only know once full use is made of this technique.”
Vindication of the crusty foulers
Stalked barnacles, which both filter feed and capture prey like tiny shrimp and polyps with hairs on their feet called cirri, have far-reaching ecological roles in cleaning seawater—and becoming food for predators including sea snails and slugs. Their super-glue strength and penchant to pile on together in crowded colonies make them a scourge to boaters, who refer to them widely as “biofoulers,” or the slang “crusty foulers.”
Griffin says he wouldn’t have imagined when he was a student assigned the squalid work of scraping barnacles from scientific instruments on the afterdeck how crucial they would prove to science. “We really need to remember how important these questions are to life here,” he says, “and to looking after our planet.”
Today, barnacles’ applications in forensics, conservation science, and biotechnology, where they inspire adhesives, are vindicating. Italian marine scientists helped prosecutors estimate that a badly decomposed body had been floating in the Tyrrhenian Sea between 65 and 90 days based on analysis of L. anatifera riding on the deceased’s pants and shoes. Researchers are also using barnacle shells in conservation biology to help track sea turtles and other marine mammals.
Charles Darwin himself spent eight years on barnacle science after finding an “ill formed little monster” during his voyage on the Beagle. He set out to write a single paper on a barnacle he called “Mr. Arthrobalanus” and ended up completing four monographs between 1846 and 1854 on diversity among hundreds of different barnacle species. The research helped shape his theory of evolution, says Power, as he saw the sweeping variation of barnacle lifestyles, still similar enough to be linked through a common ancestor.
“Eight years may seem like a long time, but in our case, since the time of the plane crash, the oxygen isotope thermometer is now calibrated for Lepas barnacle shells and there is a new methodology for constraining where the plane debris lay,” says Power.
Ultimately, says Al-Qattan at Kuwait University, one common cause kept the researchers motivated over the eight years of fits and starts. “Thinking about closure for the tens and hundreds of family members and friends of people on that plane really kept us going.”