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Coral reefs can breathe again thanks to grazing urchins

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    Kaneohe Bay, HI (KITV) — Hundreds of thousands of sea urchins are working hard to clean up the invasive seaweed suffocating corals in Kaneohe Bay.

The State’s urchin hatchery at the Anuenue Fisheries Research Center on Sand Island is housing millions of sea urchins which, upon graduation, will be relocated to help more than 50 patch reefs in the Bay. The Department of Land and Natural Resources calls the sprawling building evidence of what is arguably the most successful effort ever to control marine invasive species in Hawai’i.

David Cohen, the man who has led the urchin hatchery for more than 10 years, says raising urchins is an effective biocontrol tool against two species of introduced algae or seaweed in the Bay. “Twenty or thirty years ago,” Cohen explains, “many of the Bay’s patch reefs were completely smothered; in some cases in up to, one-to-two feet of invasive seaweed. This cuts off light to the corals and ultimately kills them.”

On Thursday, staff met up with DLNR’s Division of Aquatic Resources (DAR), and Alien Invasive Species (AIS) team to load up 1,400 urchins. They used boogie boards to help hand-place them onto the reef, which was showing more than 5% seaweed cover. Wesley Dukes, DAR’s Coral Habitat Monitoring Coordinator said, “We’ve had great success, where the majority of reefs in the bay, at this point-in-time, have algae levels that are below our 5% target. The urchins act like little goats, as they graze down the seaweed.”

The AIS team regularly monitors all the patch reefs in Kaneohe Bay and whenever one exceeds more than 5% seaweed cover, they respond quickly with another load of collector urchins. Their work has now expanded into the Waikiki Marine Life Conservation District (MLCD), which also has long suffered from an invasion of alien seaweed.

Cohen added, “This has been very gratifying over the years. What we are doing is developing biological tools for environmental mitigation and restoration. The urchins have proven to be key tools for this work in a marine environment and are instrumental in helping save near-shore reefs that are in trouble.”

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