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Crab Gas
Results of an 18-month study that used nitrogen gas to deoxygenate ship's ballast tanks suggest that getting rid of aquatic hitchikers could also help shipping companies reduce their maintenance bills.
The results of the study, conducted by researchers from the Monterey Bay Aquarium Research Institute, the Monterey Bay National Marine Sanctuary, the Elkhorn Slough National Estuarine Research Reserve, and a Japanese ship manufacturer, were unveiled in a recent issue of Biological Conservation. Researchers pumped nitrogen gas into ballast tanks continuously to remove oxygen, killing invasive species and helping slow corrosion. They then examined impacts on three invasive aquatic species - the green crab, zebra mussel, and Australian reef-building tubeworm. After only two days of nitrogen treatment, 79% of the tubeworms and 97% of the green crab larvae had died. After three days, 82% of the zebra mussels were dead. Since most ocean crossings take between two and three weeks, it is unlikely that any of the organisms would survive such a journey. While the nitrogen treatment kills the worst invaders, certain species of anaerobic bacteria and marine algae that can survive low-oxygen conditions might need further treatment, according to researcher Kerstin Wasson.
Deoxygenation's greatest selling point may be its economic benefits. According to researcher Masayasu Matsuda, corrosion rates were reduced to about 10% of the rates found in the tanks containing oxygen. The average cost of maintaining ballast tanks on a typical cargo ship (using traditional methods like painting) for 25 years is about $10.9 million, according to Matsuda. Deoxygenation would reduce that cost by at least $1 million and possibly more.
Maurya Faulkner with the State Lands Commission says the technology is a step in the right direction but needs to be tested on vessels during real voyages. Although funding for such tests might be a challenge, she says, the potential cost savings to the shipping industry is a definite plus. John Berge, with the Pacific Merchant Shipping Association, agrees: "It sounds like a win-win situation." But Berge wonders whether the technology's level of invasive species removal will satisfy regulatory agency requirements. So far, he says, there are no standards on exactly how clean ballast water must be.
Those standards may soon become clearer. In February, Northern California's U.S. District Court ordered the EPA to respond to a petition filed three years ago by environmental, fishing, and other groups asking for better controls on ballast discharge. According to Linda Sheehan with the Ocean Conservancy, the Coast Guard drafted guidelines for ballast water treatment last year that simply need to be signed off on and published. "Everybody wants this," says Sheehan. "I can't understand why they haven't been put in the Federal Register yet. There's no reason why the EPA and Coast Guard can't work together on this."
Contact: John Berge (415) 352-0710 or Linda Sheehan (415) 979-0900 LOV
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