For 40 years, scientists have tried on and off to restore sea urchins on coral reefs because they eat harmful algae that otherwise smothers ecosystems.

Now, results from a recent collaborative study show promise in urchin restocking to aid coral reef restoration throughout the Caribbean.

“Once considered a nuisance, these formerly dominant urchins are now one of the most important pieces of the puzzle for restoring reefs, following decades of destruction,” said Aaron Pilnick, who led the research for his doctoral dissertation at the University of Florida College of Agricultural and Life Sciences.

An experiment to relocate sea urchins to a reef off Key Biscayne was led by Pilnick and project scientists from the Phillip and Patricia Frost Museum of Science (Frost Science) and the University of Miami (UM) Rosenstiel School of Marine, Atmospheric, and Earth Science.

Urchin restoration may be a viable method of helping coral reefs recover and thrive, scientists say.

Volunteers collected the spiny urchins by hand from a broad area in South Florida and moved them to the restoration site off Key Biscayne. Researchers from Frost Science initiated the effort — funded in part through the Florida Department of Environmental Protection.

Volunteers included members of FORCE BLUE, a nonprofit group of combat dive veterans with a goal to help the environment.

UM and Frost Science are official partners with FORCE BLUE in 100 Yards of Hope, a coral reef restoration project started in 2021 to honor what was then the NFL’s 100th season, and also to show support America’s military veterans.

It was also through Frost Science that NFL wide receiver Mack Hollins — also a trained scuba diver — participated. Hollins and the scientists dove into the waters off Key Biscayne to place the urchins on Rainbow Reef. For nearly nine months Hollins and BLUE FORCE team member Jay Casello helped scientists regularly visit multiple dive sites, all at Rainbow Reef, to count urchins and monitor reef activity In contrast to other studies — where almost all the urchins either died or moved within weeks — researchers in this effort found that more than half the urchins remained on the reef after three months. Nearly one-fourth remained on the reef nine months later.

Even one-fourth remaining is significant, and results showed that the urchins successfully removed harmful algae from the study area.

“The survival rate is also important because these sea urchins need high densities to successfully breed, which helps reefs thrive,” said Lad Akins, curator of marine conservation at Frost Science.

“We also learned how these urchins were moving around in different habitat, which will help us develop future strategies to get them to stay in place,” said Pilnick, now a researcher at the UF/IFAS School of Forest, Fisheries, and Geomatics Sciences (SFFGS) at the Florida Aquarium Center for Conservation in Apollo Beach.

In 1983-84, 99 percent of long-spined sea urchins died in Caribbean coral reefs. Since then, researchers have been trying to restore their populations because urchins clear the reefs of algae.

In past attempts, scientists would put sea urchins on reefs in places such as Curacao and the Bahamas, only to see them leave the reefs or be killed by predators within days.

But the Rainbow Reef experiment leaves Pilnick and his colleagues hopeful.

“While we need to confirm these results in different regions, we feel optimistic about the potential benefits to Florida’s coral reef and the greater Caribbean,” he said.

“The goal is to populate reefs with Diadema [the scientific name for urchins] and figure out how to get them to stick around long enough to start eating algae.”