In shallow water not far from the Florida Keys’ famed Seven Mile Bridge, a herd of the state’s flamboyantly pink queen conchs is struggling to survive.
Warming seas and wild swings in temperature have shut down their reproductive impulses in the waist-deep water, leaving them to creep along the ocean floor, searching for food but not love. Meanwhile, just a few miles away in deeper, cooler waters, the iconic mollusks mate freely. So scientists have a rescue plan: load the inshore conchs into milk crates, ferry them to colonies in deep water, and let nature run its course.
As climate change fastracks ocean warming, the researchers hope their plan hatches enough baby conchs to help boost the flagging population.
“Once you put them in a more appropriate temperature regime, snails have a remarkable capability to heal themselves,” says Dr. Gabriel Delgado, a conch scientist with the Florida Fish and Wildlife Conservation Commission who is leading the pilot project. “Now you have a contributing member to future populations.”
Last month, Delgado and a team of scientists set out to collect some potential members from a grassy patch of ocean floor just off Molasses Key, near Marathon. Except for a brisk wind and choppy waters, the day was perfect: The Keys’ stunning turquoise waters glowed.
“If we get 50, I’ll be happy,” Delgado yelled over the boat engine as the Seven Mile Bridge loomed.
Scientists have been working for decades to understand what’s ailing the conchs and revive their populations, which were once so plentiful that the Keys declared itself the Conch Republic. At the turn of the century, queen conchs littered the ocean floor, ambling across flats and hard bottom, tidying up by grazing on algae.
“If you let them put their mouth on your finger, you can feel them licking you,” Delgado says. “It's like a cat's tongue.”
They were part of a population that once stretched across the Caribbean and seeded a powerful “larval train”—tiny conch hatchlings carried to Florida and the Bahamas by the fast-moving Gulf Stream and other currents.
But overfishing caused queen conchs’ numbers to plunge, and the shrinking herds derailed the larval train. In the mid-1980s, both Florida and federal authorities banned harvesting in the state, thinking the populations would bounce back.
Instead, the conchs languished. This year, the National Oceanic and Atmospheric Administration listed U.S. queen conchs as threatened under the Endangered Species Act.
“Surprising to no one, intensive harvest has dramatically changed the connectivity patterns of queen conch throughout the Caribbean,” says Dr. Andrew Kough, a field biologist with the Shedd Aquarium in Chicago, who has studied queen conch in the Bahamas.
With the larval train no longer sweeping conchs in from across the Caribbean, scientists now believe the only source of babies in the Keys is the Keys itself.
By the time Delgado joined the state wildlife agency after grad school in the late 1990s, scientists were wrapping up a failed project to farm conchs. The effort turned out to be too expensive and too complicated, Delgado says. Tiny conchs from state-run hatcheries didn't get carried along by currents as they would have in the wild, and it was hard to trick them into knowing when was time to stop drifting and settle down to become a growing conch. They didn't seem to be able to recognize the environment that best suited them, which would typically trigger the urge to settle. And if they did settle and grow, the young conchs didn’t know how to protect themselves once released into the wild. So scientists turned their attention to the remaining wild population.
“And what we noticed was we only observed reproduction in those offshore conchs,” Delgado says.
So in 1999 and 2000, Delgado and scientist Bob Glazer moved nearly 400 conchs from waters near Marathon to two healthy herds at offshore sites. Within months, the conchs were back in action, reproducing—and marking a critical turning point for the conch researchers.
“Florida is the only place that has tested that. And it did work resoundingly well,” Kough says. “So this is a really unique and intelligent way of going about taking animals that aren't part of the breeding population and helping increase the genetic diversity, presumably, and more importantly, the reproductive output.”
But why had they shut down reproduction in the first place? What was making the conchs near shore so indifferent to mating?
When scientists examined them, Delgado says, they found a startling clue: blank space in their tiny brains where hormones that trigger the secretion of eggs and sperm should be. The scientist who made the discovery told Delgado she’d never seen anything like it.
“She described it to me as the weirdest thing she'd ever seen,” he says. “There was nothing there.”
The ganglia that make up the conch brain appeared to be enlarged and less dense, as if the conch had prematurely aged.
“It seemed as if the nearshore animals were under chronic physiological stress,” Delgado says.
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At first, they suspected pollution from nearby islands was to blame, he says. The Keys are crisscrossed by canals that drain stormwater and crowded with marinas, restaurants, and industrial facilities. And until recently, the 100-mile-long island chain relied mostly on leaky septic tanks to handle human waste. But chemicals didn’t appear to be causing the problem. In fact, a tiny queen conch population has been thriving for years near the busy Port Everglades seaport in Fort Lauderdale. And, importantly, the conchs recovered quickly in deeper water.
“Then it dawned on us that these waters are very shallow and in the summer they get very warm and in the winter they get very cold,” Delgado says.
Those growing temperature extremes—waters in the Gulf of Mexico warmed at a rate twice as fast as global averages between 1950 and 2020—were cutting the mating season short.
“In the winter, it's too cold, and in the spring temperatures warm up a little bit and temperatures are just right: the Goldilocks zone,” he says. “Then in the summer it gets too hot and they shut down.”
The extremes left too little time for the conchs’ reproductive hormones to develop.
When Hurricane Irma hit in 2017, rebooting the population took on critical urgency.
As the massive storm crossed the Keys, it pushed around huge amounts of sand and debris. In its wake, scientists found that the population of conchs they’d been monitoring had dropped by 80%. When Ian hit five years later, the conchs had still not recovered, and the storm knocked out 40% of those that remained, even though it passed west of the Keys, Delgado says.
So time was running out.
To have a functioning herd, there need to be at least 200 conchs within a 2.5 acre area. The mollusks get around by using their lone foot to pole-vault across the hard bottom, so herds need to be dense.
“I like to use the zombie apocalypse analogy here, where if there's a zombie apocalypse and the last man's in Canada and the last woman is in Australia, it's going to take a while for those two people to find each other to repopulate humans,” Delgado says.
But moving the conchs may only be a short-term fix. While oceans warm globally, South Florida also faces an increase in ocean hotspots, Delgado says. In preparing the move, he consulted a University of Miami analysis looking at warming trends from 2004 to 2020. The study predicted that more ocean hotspots would likely begin crossing Florida’s reef to the area where the conchs were being moved
“So if the trends continue, then yes, perhaps the source populations for the larvae within the Keys could be affected like these nearshore areas,” he says.
At Molasses Key, the team quickly found several dozen adult conchs and loaded them into oversized blue milk crates to haul back to the boat. Conchs can survive out of water for about 24 hours if they’re kept wet. So researcher Justin Voss draped the crates with a tarp soaked in seawater.
Back at the dock minutes later, the conchs were tagged with numbered metal plates secured to the spiral of their shells with metal wire. And a ribbon was tied on to more easily identify them underwater. Today it’s white with red polka dots.
“We tried to be photogenic this time,” Delgado jokes.
The boats, with the conchs still under the tarp, were then loaded onto trailers and driven north to where the scientists located three herds of conch near, appropriately, Conch Key. The Gulf Stream swings closer to shore here, so the water is flushed and almost crystal clear. The relocated conchs will be added to one of the herds and then tracked over the next year and compared with other groups to see if the new recruits help boost the population.
Given their track record, Delgado is hopeful the move could buy Florida’s queen conchs more time.
“There have been studies on mud snails where people have excised their cerebral ganglia and it grows back in its entirety,” he says. “So the gastropods have remarkable, what's the word I'm looking for?” Survivability? “Sure.”
This story was published in collaboration with Science Friday.
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