Learn & Explore/Programs & Initiatives/Urchin Hatchery
Urchin Hatchery
Raising native sea urchins to help reefs stay healthy by keeping invasive algae in check.
Sea Urchin Hatchery
The best way to keep invasive algae under control is to have enough native herbivores in the ecosystem. At the Ānuenue Fisheries Research Center, the DAR Sea Urchin Hatchery breeds and raises native Hawaiian collector urchins (Tripneustes gratilla) to help fight invasive seaweeds in Hawaiʻi.
Usually, invasive algae are first removed by hand or with mechanical tools. But if there aren’t enough native herbivores—like these collector urchins—the algae will simply grow back.
To prevent this, DAR removes the invasive algae and then places hatchery-raised urchins onto the reefs to keep the algae from returning. These urchins graze on the regrowing seaweed, acting like underwater gardeners (or like goats clearing unwanted brush).
When invasive algae are kept in check, corals finally have the space and sunlight they need to grow and stay healthy.
Hatchery Process
Collection and Spawning
- Once a month, divers collect about 20 wild adult urchins from different sites along the south shore of Oʻahu.
- The collected urchins are brought back to the Ānuenue Fisheries Research Center.
- At the facility, staff gently stimulate the urchins to encourage them to spawn.
- The urchins then release their gametes into prepared plastic containers.
Larval Propagation
- After the gametes are collected, they’re mixed together and moved into large cylindrical tanks.
- Since urchin larvae are free-swimming, the water in the tanks must keep them constantly suspended.
- Inside these tanks, the larvae feed on phytoplankton and move through several growth stages.
- This early development period lasts for about three weeks.
Settlement and Growth
- After about three weeks, the larvae settle and start to take on the shape of a real urchin.
- At this stage, they’re still extremely tiny (from the size of a pencil tip to a thumbtack), so their mouths are very small.
- Because of that, they feed on the biofilm that naturally grows inside the tanks for 1-2 months.
- As the urchins grow and their mouths get bigger, they transition to eating macro-algae.
- Once they reach this stage, their growth rate increases quickly.
Transplantation
- After about 4–5 months, the urchins grow to around the size of a quarter, making them big enough to handle and move to the reef.
- Once released, they hide immediately, as juvenile urchins tend to stay tucked away while they feed.
- Young urchins graze on invasive algae, and as they grow too large to fit in reef holes, they eventually emerge and roam the reef, slowly moving around in search of food.
- The first group of hatchery-raised urchins was released into Kāneʻohe Bay in January 2011.
- Since then, the hatchery has released 600,000 sea urchins across Hawaiʻi, helping restore over 227 acres of reef in Kāneʻohe Bay.
- The program has also expanded its efforts to the Waikīkī Marine Life Conservation District.
Voice of the Sea
Voice of the Sea is a Hawai‘i Sea Grant program that highlights research, science, and cultural practices throughout Hawai‘i and the Pacific. In this Episode, watch Urchin Hatchery staff explain the importance of culturing sea urchins for algae management in Hawai‘i.
Other Topics
Explore related restoration efforts, including aquaculture stocking and coral restoration nursery work that support healthy reef ecosystems.