The Florida Aquarium, University of Florida and the Florida Fish and Wildlife Conservation Commission have successfully reared and released nearly 200 long-spined sea urchins off the coast of the Florida Keys.

The largest single release of the reefs top grazer and a significant achievement for reef restoration.

Long-spined sea urchins, Diadema antillarum, are a critical part of the coral reef ecosystem because they clear algae of the substrate, which allows coral communities to grow on the substrate.

But in 1983 and 1984, the sea urchin suffered mass mortality throughout the Florida, the Florida Keys and the Caribbean. The demise of this herbivore contributed to a phase shift of Caribbean reefs from coral-dominated to alga-dominated communities.

“With their long black spines, these urchins are instantly recognizable as one of the most striking creatures in the Atlantic Ocean” said Alex Petrosino, a biologist at the Florida Aquarium. “What is less commonly known is these urchins provide a vital service, living out their lives, eagerly scouring over the reef surface and feeding on the fleshy algae that is fueled by pollution and can suffocate healthy coral reefs.”

Last month, the urchins, about 2 to 4 centimeters in diameter were placed in several locations near Sombrero Reef at Yellow Rocks and Delta Shoals reefs. Some were placed among outplanted corals at restoration sites and some were placed underneath experimental shelters to better protect the urchins from being eaten by lobster, crabs and other predators, said Keri O’Neil, Florida Aquarium’s manager and senior scientist.

Coral reefs around the world are dying off at an alarming rate. The Florida Aquarium is playing a key role in researching and breeding dozens of coral species found along Florida’s coral reef, which stretches from the Dry Tortugas to north of Palm Beach, in hopes of restoring coral populations with diverse offspring that may be more durable to threats such as disease and climate change.

Simultaneously, aquarium researchers are helping discover ways to rear volumes of urchins and other grazers that clean coral reefs so they can thrive.

Though urchins like these were once abundant in the Caribbean, the world nearly lost its entire long-spined sea urchin population in the 1980s because of an unknown disease. The urchins were never able to fully recover on their own.

Rearing spiny urchins is a thorny process at best, as it is one of the hardest invertebrates to rear, O’Neil said. For several years, Florida Aquarium researchers have been working collaboratively with the University of Florida developing ways to rear and foster urchins that help clean algae from reefs.

To begin that process, specialists with the Florida Fish and Wildlife Conservation Commission’s Fish and Wildlife Research Institute collected adult urchins in the Florida Keys.

The adult urchins were transported to the Florida Aquarium’s Center for Conservation in Apollo Beach, Florida. In the laboratory, researchers at The Florida Aquarium and University of Florida spawned these individuals and collected the fertilized eggs. Urchins broadcast spawn, and each adult can produce millions of eggs and sperm in each spawning event.

Around 400,000 fertilized eggs were selected for grow-out and were placed into custom designed containers called kreisels, which have a circular flow of water that keeps the urchin larvae floating constantly in the water column while they develop.

After about 35 days, the urchins were able to settle out of the water column and were moved into larger tanks and raised for another six and a half months until they could be relocated to the ocean environment in the Florida Keys.

“We are in a race to help the world’s coral reefs, and this release of critically important algae grazers is a huge step forward” O’Neil said. “I am immensely proud of our team, and our partner institutions, who came together to find healthy and supportive methods to foster hundreds of urchins and release them into the wild.”

This project is considered the largest restocking effort known in the last 20 years and aims to learn more about how to successfully transport, outplant and monitor these sea urchins. These areas of the Florida Keys have lacked long-spined sea urchins in recent decades.

Colleagues at FWC designed a multifaceted research project, where each reef site included six different research plots, where experimental plots were enhanced with urchins, corals and/or artificial shelters. The FWC staff designed the experiment to see how the urchins will respond at the different treatment levels and will monitor these sites frequently over the next several months.

Importantly, UF gained state-approved health certification to release aquarium-raised animals back into the wild. Such work must be conducted by an approved veterinarian. This process is developed separately for each species released into the wild, based on their particular health concerns.

The health certification process ensures that only healthy animals are released and do not put wild populations at risk. The Florida Aquarium, University of Florida, and the Florida Fish and Wildlife Conservation Commission worked closely together to develop the health certification process for diadema sea urchins and tested the process for the first time with this release. Roy Yanong from the University of Florida conducted the inspection along with Lindsey Waxman from the Florida Aquarium. This work lays the foundation for all future releases of aquarium-reared sea urchins into the wild.

Partners include the Florida Aquarium, University of Florida, and Florida Fish and Wildlife Conservation Commission.

Sea urchin propagation work was made possible with support from the NOAA Restoration Center, NOAA’s Coral Reef Conservation Program, the National Fish and Wildlife Foundation and the Florida Fish and Wildlife Conservation Commission.