Urchins Rule

UrchinMankind—both the builder and the destroyer—has left his mark on the world. But it’s also true that the world is shaped by the minute operations of seemingly insignificant organisms. Nowhere is this more obvious than in the sea and along its margins. At research centers like C-MORE, scientists study how microscopic organisms regulate the chemistry of the sea, and in their dead trillions constitute the thick muck of the ocean floor. I’ve written elsewhere about how the sand on coral islands is composed of the detritus of coralline algae and tiny coral fragments gnawed off the reef by the obdurate beaks of parrotfish. And, in one of my favorite examples of small animals changing the landscape, we know that much of the rocky coastline of tropical, basaltic islands like Oahu is shaped by the incessant scraping spines of sea urchins.

Urchins also turn out to be major players in the shaping of ecosystems.

For the last three years, the Department of Land and Natural Resources, Division of Aquatic Resources, has been trying to control the spread of Kappaphycus, an invasive algae that’s been slowly smothering the coral reefs in Kaneohe Bay. Any paddler or snorkeler or boater can attest to the changes in the reefs over the last decade, as the structural habitats provided by rice coral, cauliflower coral, and coralline algae have increasingly given way to a shaggy coat of seaweed that blocks out the sunlight and impedes the growth of the coral.

Eight years ago, the state and its nonprofit partner The Nature Conservancy began by duplicating a program TNC had already successfully implemented on Moanalua Bay, using a so-called Super Sucker—essentially, a barge with a giant vacuum attached—to suck enormous quantities of Kappaphycus off the reef. Amazingly, it works. The Super Sucker on Kaneohe Bay can extract over 1,000 pounds of seaweed an hour (much of which is used by farmers to supplement their soil.) The problem, though, is that the treatment doesn’t last. Even after nearly clearing the reef of the invasive algae, the lush growth returns to pre-treatment levels within a matter of months. Recently, TNC added a second barge to the Kaneohe Bay program, but even if the two barges work full time, they can’t keep up with the prolific growth of Kappaphycus.

Enter the urchin. In 2010, DLNR began raising collector urchins at its Anuenue Fisheries Research Center on Sand Island. The idea is to use these natural grazers to hold down the growth of seaweed in areas of Kaneohe Bay already treated by the Super Sucker. (The collector urchin is a native species to Hawaii waters, though not often found in the Bay.) In a demonstration project, TNC cleared a 3,000 square-foot section of patch reef in the middle of the Bay, then distributed collector urchins over half the reef, leaving the other half without urchins. On the side with urchins, the Kappaphycus growth was kept to a minimum; the urchin-free side quickly reverted to a seaweed jungle. That’s the power of small animals to shape the world.

And, at least in this one instance, people noticed. Since 2011, the state has distributed more than 100,000 collector urchins onto the reefs of Kaneohe Bay.

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