Sea Urchin Hatchery Celebrates Ten Years
By: Caitlin Tsuchiya, UHH MOP Student

Many environments in Hawaiʻi are suffering from the impacts of invasive species, and coral reefs are no exception. In Kāneʻohe Bay, red algae suffocates coral reefs and outcompete native algae, thriving in a predator-free environment. However, a combination of human effort and hatchery-raised sea urchins is currently successfully combating these pernicious algae, and the Kāneʻohe urchin hatchery has recently celebrating their 10th anniversary in their quest to quell these invaders.

Hawaiʻi was one of the first states to have a comprehensive aquaculture development plan in the 1970s. In 1974, a university aquaculture researcher introduced foreign red algae of the genera Kappaphycus and Eucheuma to Kāneʻohe Bay in experimental pens. These algae, which are native to Southeast Asia, are commonly harvested for their carrageenan, a substance used in many foods for its thickening and preservative abilities. However, in their new environment, which lacked their natural predators, the algae had free reign of Kāneʻohe Bay’s coral reefs. While native collector sea urchins, which do eat these species, were common in many reefs in the state, they occurred in low numbers in the Bay.

The aforementioned red algae form in large knotted mats or clumps, with thick spiny branches sticking out in erratic directions. They grow quickly and spread via fragmentation, where a piece of a branch can regenerate into a separate plsnt. They can sometimes grow completely over coral, blocking it from receiving sunlight. Thus, these algae have earned the moniker “smothering seaweed”.

In 2005, an underwater vacuum device called the “Super Sucker” was developed- a 40-horsepower pump and large hose which can suck up to 800 pounds of algae per hour. While this tool removed the majority of the algae, often small fragments were left behind. The urchins feed on those fragments, controlling regrowth.

In 2009, the State of Hawaiʻi started a sea urchin hatchery in an old prawn hatchery at Sand Island, Anuenue Fisheries Research Center, where sea urchins could be spawned and raised. It became an official operation in 2010. The hatchery is a multi-agency effort, involving the University of Mānoa Pacific Cooperative Studies Unit (PCSU), the State of Hawaiʻi Division of Aquatic Resources (DAR), NOAA, US Fish and Wildlife Service, and the State of Hawaiʻi Department of Transportation.

Sea urchins were first released in 2011, and since then, more than 600,000 hatchery-raised urchins have helped treat nearly 230 acres of reef in Kāneʻohe.They’ve also expanded to tackle invasive algae in the Waikiki Marine Life Conservation District. Hatchery manager David Cohen describes the sea urchins as “little goats, or little gardeners, [as] they work their way around the reef and eat the invasive seaweed.” He further explains that if humans did this mechanically, they would have to return every six to eight months to remove seaweed. Once a month, divers collect sea urchins from Oʻahu’s south shore. In the lab, the urchins are gently agitated to encourage them to spawn and release their eggs or sperm.

Once collected, the gametes are combined in large cylinder tanks where they are free-swimming and feed on phytoplankton for about three weeks. The larvae then settle and take the shape of a true urchin, where they feed on the biofilm that naturally forms inside their tanks for up to two months. After another 4 to 5 months, the urchins are about the size of a quarter and large enough to be handled and transplanted to reefs that need their gardening expertise!