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"All experiments to date show that at a high density collector urchins will stop invasive algae from growing back."


 

By Evelyn Wight

Native Hawaiians had specific names and uses for various species of sea urchins. Species such as wana and hā‘uke‘uke were collected for food, but the Hawaiians did not value the collector urchin as a food source. In fact its Hawaiian name, hāwa‘e, means useless, and the term hāwa‘e kai nui was once a common insult meaning a useless person full of liquid.

But now, hāwa‘e are shedding their past and re-inventing themselves by playing a vital role in marine conservation. Because they are the only native marine species in Hawai‘i that find the worst invasive algal species appetizing, scientists have turned to them for help in the battle to save our coral reefs.

In Kāne‘ohe Bay, invasive algae smother patch reefs and are quickly spreading into the north end of the bay. The Conservancy has been working with the State to remove the aggressive algae using the Super Sucker underwater vacuum. While the Super Sucker successfully removes the algae, without hāwa‘e to keep them in check, the algae eventually come back.

The State is currently cultivating thousands of hāwa‘e at its hatchery on Sand Island.

When they reach a certain size—about the size of a dime—the urchins are released onto reefs that have been cleared of invasive algae and begin nibbling away at any new growth. Although they are full of liquid instead of muscle (as the insult suggests), their internal vascular system uses that water and suction to enable them to proficiently move around on thousands of tiny tube feet.

Hāwa‘e are called collector urchins because they pick up small things from the reef and put them on their backs for protection. They are also exceptionally good at hiding in reef cracks and crevices, eating what they find there. The urchin’s mouth, called Aristotle’s lantern, is a beak-like mouthpiece that it can extend a half-inch away from its body. Once it’s out, it can be efficiently turned from side to side to scrape away every last morsel.

All experiments conducted to date show that at a high density, collector urchins will stop invasive algae from growing back, allowing struggling corals to recover.

With assistance from the hāwa‘e, Kāne‘ohe Bay is on its way to healthier coral reef and fish populations, while the urchin itself has clearly earned a new place of value and respect in its island home.


 

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