How to raise little ‘lawn mower’ urchins for coral reefs

New research points to a better way to breed long-spined sea urchins for recolonizing coral reef ecosystems.

Pollution, disease, over-harvest and other factors seriously threaten these ecosystems. For millennia, long-spined sea urchins helped keep reefs intact. They eat algae that can kill or seriously damage corals. Without coral, reefs suffer severe consequences including a reduced ability to support fish.

By the mid-1980s, more than 90% of the sea urchins roaming the coral reefs of the western Atlantic and Caribbean died for reasons scientists have not yet determined. The population of the long-spined sea urchin (Antillar diadema) was slow to recover on its own. That’s why scientists, including Josh Patterson, are stepping up efforts to improve sea urchin populations.

“You could call these sea urchins the lawnmowers of the reef,” says Patterson, associate professor of fisheries and aquatic sciences in the University of Florida’s Department of Food and Agricultural Sciences. “They eat fleshy algae that grow out of control on coral reefs and eventually suffocate the coral.”

The recovery ecologist is attempting to bring more sea urchins back to an area roughly encompassing the seas off the Florida Keys, Bermuda, the Yucatan Peninsula, Aruba and the Virgin Islands. He’s a small step closer to the overall goal of reviving the population of vital echinoderms.

Patterson used about 200 sea urchins for his final experiment — a surprisingly high number considering how difficult they are to breed. “You could collect 200 wild sea urchins without too much trouble; Growing 200 of them via aquaculture is much more difficult,” he says.

As described in the journal aquaculture reportshe and his colleagues showed that by feeding dried seaweed to long-spined sea urchins in baby culture, they can help them grow faster and behave more like natural sea urchins than if you feed them commercial pellets that are usually fed to herbivorous fish in saltwater aquariums be fed.

“When the sea urchins behave naturally, they’re more likely to find shelter on the reef and survive to eat the algae,” says Patterson.

As for this natural behavior, long-spined sea urchins are nocturnal. For the experiment, the scientists came every six hours — at midnight, 6 a.m., 12 p.m., and 6 p.m. — and recorded the proportion of sea urchins in each tank that were actively feeding, foraging, or hiding. Those fed the dried seaweed were more likely to eat at 6am, a time when you would expect them to be dining.

The trick is now: do the sea urchins reproduce on the coral reefs?

“The ultimate idea is to try and breed thousands upon thousands of sea urchins to replenish the reef to eat the algae overgrowth,” says Patterson, a faculty member at the Tropical Aquaculture Lab. “These results are steps towards this ultimate idea. And you want to be able to produce them faster.”

Patterson and his colleagues conducted the experiment at the Florida Aquarium’s Center for Conservation in Apollo Beach, where Patterson works.

Source: University of Florida

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