In the annals of biology, long-spined sea urchins rank high among the least loved.
With spines that allow them to grow to the size of a volleyball, all loaded with painful toxins, Florida and Caribbean sea urchins have been the bane of divers.
“They’re pesky little devils,” said Lad Akins, the curator of marine conservation at the Phillip and Patricia Frost Museum of Science who’s been diving in Florida for four decades. “Or they used to be.”
They used to be because in the early 1980s, 97% vanished from the reefs in about a year. Scientists believe a disease moved through the Panama Canal and traveled up the reef tract. Infected urchins would lose their spines and die, in a single day, Akins said.
“Imagine every square meter of reef with three to five urchins,” he said. “Now, you are lucky to find a sea urchin in one hundred square meters of reef.”
After they were gone, scientists came to better appreciate their value. A voracious grazer that gobbles up algae, the urchins helped keep the reefs tidy, with cleaner surfaces that better allowed coral to attach and grow. Without them, coral struggled.
That struggle has only worsened as coral diseases worsened — white band disease wiped out most of Florida’s elkhorn coral not long after the urchins disappeared — coupled with warming waters fueled by climate change that ignite bleaching events.
Since 2014, a new disease first detected off Virginia Key has infected nearly two dozen species of mounding coral on Florida reefs, spreading south into the Caribbean.
Those dire conditions have triggered an international coral rescue effort, with researchers hurrying to develop more resilient coral, increase genetic diversity and expand coral nurseries.
“It was absolutely a call to action,” Akins said.
Stepping up to save sea urchins
Now sea urchins are being added to the mix of rescue efforts. This month, Akins led a team that included the University of Miami, the Florida Aquarium, Force Blue, and Secore International, to place urchins on a reef targeted for restoration near Key Biscayne.
Divers spent several months collecting just over 200 urchins from reefs across Florida, stored them in a quarantine tank at Florida International University so they could become familiar with one another, then placed them in groups of 40. Some were placed on parts of the reef with transplanted coral, and some were planted in unrestored parts of the reef. Researchers will spend the next several months studying how the urchins behave.
"This is one site, Rainbow Reef, with these five plots. But we have an entire Florida coral reef system, from Martin County all the way down through the Keys, that needs this kind of work,” Akins said. “So there's a good chance it will be collecting urchins and replicating this work in other areas.”
Researchers believe proximity plays a big part of urchins being able to sustain their population, which also explains part of why they have never recovered.
“If your closest partner is 100 meters away on a reef, you could imagine those eggs and sperm will get very diluted and fertilization rates will be really low,” he said.
Taking a play from coral rescuers, researchers have also started breeding urchins in nurseries to restock reefs. That effort made a big leap forward in 2019 when Florida Aquarium researchers succeeded at breeding urchins in numbers plentiful enough to move to reefs.
Akins said while they eventually plan to use lab-bred urchins, they wanted to start experimenting with wild urchins to see if they could better understand what conditions lead to healthy urchins.
“Let's see if the urchins stay. Let's see if the urchins eat the algae. Let's see if there is a relationship between the structure provided by the outplanted corals and the urchins to see if they're benefiting each other,” he said.
One week after they deposited the urchins, Akins said the urchins were still clustered together. They plan to return this month to check their progress.
'There's an effect on everything when something disappears'
Aside from the reef health, Akins said the urchin itself warrants saving as a marvel of engineering.
“It's amazing that they can control those spines. When you see them on the reef, typically you see all the spines out, which is somewhat of a normal defensive posture for the urchin,” he said.
When divers unloaded them on the reef, they all assumed the same position as they drifted downward.
“It looked almost like a mohawk haircut. All the spines went up,” he said. “They are beautiful. The two feet and the spines are all controlled through basically a hydraulic network. So they pump water to control the movement of their feet and the spines.”
Then there’s the creepy mouth. Located on the urchin’s underside, it’s shaped like a perfect circle, ringed by teeth. It’s called Aristotle’s lantern, named for the original logician, who is also credited with being the first scientist.
“He was the first person to do this, actually engage in this rather intangible activity we call science,” evolutionary biologist Armand Leroi said in a 2018 lecture.
Aristotle first described them in his "Historia Animalium," saying the mouth and the urchin’s inner workings were contained in what looked like a horned lantern.
In his book, Aristotle also described what scientists now know is the critical interdependence nature needs to succeed. "Nothing is accidental in the works of nature. Everything is absolutely for the sake of something else," Leroi translated during his lecture.
“Scholars call this the invitation to biology,” he said.
Without urchins, reefs not only lost a hardworking housekeeper, but a food supply, Akins said.
“Imagine each sea urchin putting out millions of eggs multiple times throughout the year. And all of those eggs being food for other organisms, even corals and fish. We lost all of that when we lost the sea urchins,” he said. “It's never as simple as 'A eats B.' There's an effect on everything when something disappears.”
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