Unleashing an Army of Sea Urchins to Save a Coral Reef
A Restoration Story
By Dana Bivens, A Public Affairs Officer with the U.S. Fish and Wildlife Service
Early in the morning on February 2, 2005, the 555-foot bulk carrier M/V Cape Flattery ran aground outside Barbers Point Harbor in Oʻahu, Hawaiʻi. The harbor is located on the southwestern corner of the island and is surrounded by vast coral reefs. This port plays an important role for cargo ships coming and going from Hawaiʻi, and large ships navigate a channel into the harbor to avoid the shallow reef shelf near the entrance. Disaster struck when the Cape Flattery missed this channel and hit the reef while still loaded with thousands of tons of cargo.
Coral reefs play an integral part in the marine ecosystem surrounding the Hawaiian Islands. Often called the “rainforests of the sea,” tropical coral reefs teem with fish, invertebrates, sea turtles, and marine mammals. The corals themselves are living organisms which rely on healthy oceans to grow and provide habitat for the thousands of species that depend on them.
When the Cape Flattery missed the harbor’s entrance channel, it hit the surrounding reef and lodged on the seafloor. At the time of its grounding, the cargo ship contained 27,000 metric tons of bulk cement powder plus 147,000 gallons of fuel oil. If the oil were somehow released, it would have been devastating for all creatures living in the vicinity. The threat was real.
Rescue workers soon mobilized and tried various ways of removing the ship from the reef. First, they attempted to haul the ship off the seafloor using heavy cables attached to tugboats. Unfortunately, these cables caused additional damage as they dragged across the reefs and crushed the delicate corals in their path. The team then tried to lighten and refloat the ship by unloading its cargo. Although the oil was safely removed, large amounts of powdered cement spilled into the ocean, causing even more damage to the ecosystem. Finally, after nine days, the crews offloaded enough fuel and cement to refloat the ship and drag it off the reef. Crushed corals, a scarred seabed, and polluted water remained in its wake.
After the ship was removed, a team of biologists from the U.S. Fish and Wildlife Service (Service), National Oceanic and Atmospheric Association (NOAA), and the State of Hawaiʻi’s Department of Land and Natural Resources (DLNR) arrived at the site to assess the damage. Nearly twenty acres of corals, were crushed or broken from the ship grounding, deployment of the ship’s anchor, and the use of steel tow lines that dragged across the coral beds. Additionally, spilled cement powder polluted the water, harming many of the living organisms on the sea floor.
So what happens now? A large vessel has caused irreparable damage to Hawaiian reef. What are the next steps to ensure that the reef is restored, or that the damage to the reef has been properly mitigated? Federal agencies like the Service use a legal process called a Natural Resource Damage Assessment (NRDA) to determine the extent of damage caused by groundings like this, and to develop plans to offset the loss of natural resources.
When a shipwreck occurs, affected resource management agencies work together to identify the extent of natural resource injuries, the best methods for restoring them, and the type and amount of restoration required. Essentially, the responsible party provides funding to restore the ecosystem, or to conduct work to mitigate the damage and therefore protect the value of the resource for the people, plants, and wildlife that depend on the habitat.
Using this damage assessment process, a Natural Resource Trustee Council (Trustees) consisting of the Service, NOAA and DNLR, reached a $7,500,000 settlement with the owners of the vessel in 2013. The Trustees determined that the best way to restore the damaged area would be to let the reef recover naturally over decades. The funding from the settlement, therefore, would be invested to support ongoing efforts to recover coral reefs throughout Kāneʻohe Bay, located on the northeastern side of the island of Oʻahu.
In Kāneʻohe Bay, two species of invasive algae known as kappaphycus and eucheuma had been accidentally released into local waters through human activities, not related to the shipwreck. The algae damaged the reefs by overgrowing and smothering the coral, effectively killing the ecosystem. The Trustees decided that the best way to recover the reef would be to invest the NRDA resources into eradicating these invasive plants. But how do you eradicate algae from a tropical reef?
First the team used the Super Sucker, an enormous underwater vacuum, to suck up the algae and filter it out of the water. While this removal method is effective, it is extremely slow, and by the time biologists cleaned an area of the reef, algae would have already begun to regrow. The team needed a way to keep the cleaned areas free of algae before it had a chance to recolonize.
The Solution: Deploy the sea urchin army. Sea urchins feed on marine algae and had been successfully used to control invasive algae in past experiments. The Trustees decided to use urchins in areas cleared by the Super Sucker to remove the last traces of the non-native plants and promote long-term reef recovery.
But how would the Trustees find and distribute enough sea urchins to make a difference? Here the State of Hawaiʻi stepped in to lead the charge. A team of biologists, led by David Cohen from DLNR’s Division of Aquatic Resources, developed a way to raise sea urchins in a repurposed fish hatchery. Once a month, divers gather urchins from the surrounding reefs and bring the adults to the Anuenue Fisheries Research Center in Honolulu. There, biologists collect the eggs and sperm from the adult urchins and place them together in large cylindrical tanks where they combine to form urchin larvae. The urchin larvae are free swimming, unlike their bottom-dwelling adult parents, and for the next few months the larvae swim in the tanks, feed on phytoplankton, and go through many growth stages. Over time the larvae begin to look like miniature adults and settle at the bottom of the tanks and continue to feed and grow until they are large enough to battle the invasive algae.
After four to five months, the juvenile urchins are about the size of a quarter and are ready to be released into the wild. The urchin armies are then deployed to target sites throughout the bay where invasive algae are the greatest threat. In 2011, the Trustees released the first urchin platoon and it was a resounding success.
Since 2011, DNLR has raised and released nearly 590,000 urchins on 22 reef sites, recovering 227 acres of habitat. The goal is to keep the level of invasive algae cover below five percent in the treated reefs, and in most sites the urchins helped the scientists achieve this target. In addition to preventing recolonization in areas treated by the Super Sucker, the urchins proved to be more effective in removing algae deeply imbedded in corals or hiding among loose rock where the Super Sucker was unable to reach. In areas treated by the urchins, biologists noted heathier corals and more abundant wildlife.
The Kāneʻohe Bay sea urchin restoration project is ongoing, with the first decade a success in recovering the bay’s underwater rainforests. Nature’s soldiers are helping the Service and our partners win the war against aquatic invasive species and protect native biodiversity. Restoring the reef will help provide habitat for thousands of marine plants and animals, food for seabirds, and amazing recreational opportunities for divers and anglers who visit the beautiful tropical reefs throughout Hawaiʻi. Keep fighting, troops!
The U.S. Fish and Wildlife Service works with others to conserve, protect, and enhance fish, wildlife, plants, and their habitats for the continuing benefit of the American people. For more information, connect with us through any of these social media channels at https://www.facebook.com/PacificIslandsFWS, www.flickr.com/photos/usfwspacific/, or www.twitter.com/USFWSPacific.
