State expanding project using of oysters to clean Pearl Harbor

Aiming to replicate the water quality impact of oysters on places such as Maryland’s Chesapeake Bay, the state Division of Aquatic Resources on Tuesday announced the expansion of its own oyster-growing experiment with the target of helping to clean up Pearl Harbor.

Bruce Anderson, division administrator, said the Department of Land and Natural Resources plans to escalate a project that has successfully grown several thousand oysters in Pearl Harbor’s West Loch over the past year.

“They are doing extremely well,” Anderson said at a news conference at Kualoa Ranch’s Molii Fishpond, where most of the oysters served in Hawaii’s restaurants are raised.

“It’s all about environmental restoration,” Anderson said. “We’re not planing to eat the oysters, although they’re probably very edible.”

There was a time when Hawaii’s largest natural estuary was home to lots of oysters, first the native Pinctada radiada, or pearl oyster, and later an introduced species, Crassostrea virginica, or the Eastern oyster.

But too much dredge-harvesting of oysters during the Hawaiian monarchy and excessive polluted runoff during the 1900s severely harmed Pearl Harbor’s oyster-growing capability, and today oysters are challenged for survival by layers of sediments, petrochemicals and heavy metals, officials said.

“The fundamental question is, can oysters grow and thrive in the waters of modern-day Pearl Harbor?” said Paul Bienfang, president of Analytical Services, the contractor hired to oversee the experiment.

If the oysters can thrive, he said, there’s an opportunity for a natural “bioremediation” to increase water clarity and allow light to penetrate throughout the water depths, which will enable bottom-dwelling aquatic communities to make a comeback.

The saltwater mollusks, considered the most popular U.S. seafood during the 1800s and 1900s, are known to naturally remove microorganisms and nutrients from the water and help prevent oxygen depletion that can kill fish.

Anderson said oysters might be small but are capable of doing powerful things in groups.

“Each of these oysters filter 30 gallons of water a day. If you have hundreds of millions of oysters, which is not unusual in a large water system, you are filtering a huge amount of water every day — 365 days a year. Even a few hundred million, which is not that many oysters, can do a tremendous amount in trying to clean up the harbor, or at least in the West Loch area,” he said.

National Ocean and Atmospheric Administration studies at Chesapeake Bay have documented the water quality impact of oysters.

NOAA estimated that oysters at one time were able to filter all the water in the bay in about a week. But over-harvesting, disease and habitat loss led to a sharp decline in oyster numbers, and now it takes the current oyster population about a year to filter the same amount of water.

Bienfang said the West Loch oysters over the past year have thrived to the point where they have been growing in population at least 10 percent a week.

“It appears the first step in this natural remediation has been successful,” he said.

The state spent $100,000 for the one-year study and will apply for grants for several hundred thousand more, Anderson said.

Anderson, former president of the Oceanic Institute in Waimanalo, designed the floating cylindrical cages that were assembled to support the oysters while they grow.

The cages are made of coated steel wire mesh with plastic bucket lids covering the ends. Inside is a 4-inch-diameter float that keeps the cage suspended and off the seafloor, where the oysters would be vulnerable to crabs and other sea creatures.

Anderson introduced the cages to Kualoa Ranch about 10 years ago, when it decided to utilize the 125-acre Molii Fishpond for oyster growing. Molii is Hawaii’s largest and oldest working fishpond.

Ranch President John Morgan said not only has the water quality improved in the fishpond, but the oyster operation has taken off to where it is producing 10,000 oysters a month. It is now the ranch’s most profitable agricultural venture, even more lucrative than the ranch’s 500 head of cattle, he said.

The popular Pacific oyster, or Crassostrea gigas, is being used for the Pearl Harbor project because it has shown good survival and spectacular growth rates in isle fishponds, officials said.

Anderson said several thousand more oysters will be introduced into West Loch during the project’s next phase, including a different species, the Eastern oyster, to see how it performs.

Anderson said that if the experiment continues to be a success, he can see a day where oysters will be used to help rehabilitate the water of such places as Hilo Bay and even the Ala Wai Canal.