Ballast Water Deoxygenation:
A New Technique for Preventing Species Introductions
that Should Make Everyone Happy

Invasions by non-native aquatic species are increasingly common worldwide in coastal habitats. Estuaries, in particular, harbor large numbers of introduced species. For example, there are about 250 known invasive species in San Francisco Bay and Delta. Although the effects of many introduced aquatic species on habitats they colonize remain largely unknown, some clearly have had serious negative influences. Impacts often include decreases in abundance and even local extinction of native species, alteration of habitat structure, and massive economic costs due to biofouling.

Water carried in ship ballast tanks is an important mechanism for the introduction of exotic species. photo MBNMS

Probably the most important mechanism for the introduction of aquatic species is transport in ship ballast tanks. Vessels commonly pump water into ballast tanks or into empty cargo holds in one port (to increase the draft, regulate the stability, or maintain the stress loads) and discharge it at another. Examinations of ballast water when ships arrive into port after long ocean crossings have revealed living and viable bacteria, protists, dinoflagellates, diatoms, zooplankton (including numerous larval forms), and in some cases small benthic invertebrates and fishes.

A lot of effort has therefore been put into developing ways to kill or remove organisms from ballast waters. Dozens of strategies have been suggested, including approaches like intensive filtration, thermal treatment, and biocides. Although several of these approaches appear promising, they all have one major limitation: to date, all proposed ballast water treatments will result in significant costs to the vessel owners.

Until a ballast water treatment is mandated by international law, it is extremely unlikely that the shipping industry will voluntarily employ anything that will cost them money. Therefore, the key to reducing the potential of aquatic introductions is to find a technique that is effective at killing or removing organisms and that will be accepted by the ship owners. We believe we have found such a technique.

Ballast tank corrosion is a huge problem for the shipping industry. Rusting reduces ship life and currently can only be managed by costly and time-consuming painting and maintenance. Recently, however, scientists from Sumitomo Heavy Industries of Japan have found that purging or removing the oxygen from ballast tanks with nitrogen gas is a cost-effective technique for reducing corrosion.

Recognizing the potential for this technique to kill organisms in ballast waters also, we studied the effectiveness of deoxygenation in preventing species introductions. In particular, the oxygen tolerance of larvae from diverse invasive invertebrate species was tested (two of which nuisance species occur in the Sanctuary) and focused literature reviews were conducted. Larvae of the Australian reef-building tubeworm (Ficopomatus enigmaticus), the European green shore crab (Carcinus maenas), and the European zebra mussel (Dreissena polymorpha) were found to survive only a couple of days under the low oxygen conditions produced in ballast tanks treated with nitrogen to prevent corrosion.

The results from our laboratory study were similar to what we found in the literature for the oxygen tolerance of various other aquatic species: most organisms will only survive hours to days under low oxygen conditions, while cargo ships are typically at sea for weeks. However, it is also important to point out that there are some organisms—like facultative anaerobic bacteria—that may survive the deoxygenation of ballast water.

In a 1996 report the National Research Council proposed that successful ballast water treatments should be 1) effective at killing potential invaders, 2) safe for shipboard crew, 3) environmentally benign, and 4) affordable for ship owners. First, our results show that deoxygenation is highly effective at killing animal invaders but may be less effective for other taxa, particularly those adapted to low oxygen environments or with resistant stages such as cysts. Second, with proper equipment and training, nitrogen (which makes up 78 percent of the air we breathe) poses no major threats to crew safety. Third, hypoxic ballast water would appear to be relatively benign when discharged. Hypoxic water will mix rapidly with shallow oxygenated water in harbors and therefore create little danger for native estuarine organisms. However, if temporary exposure to reduced oxygen levels does prove harmful to some native organisms, it would be simple to re-oxygenate water before release. Finally, ballast water admirably meets the fourth criterion: rather than an added expense for ship owners, it actually represents a net savings due to the significant decrease in corrosion. To our knowledge, this is the only example of a ballast water treatment technique with economic incentives for the shipping industry.

The National Research Council evaluated ten candidate technologies for shipboard treatment of ballast water and concluded that intensive filtration, use of biocides, and thermal treatments held the most promise. Deoxygenation did not receive high priority because of its failure to kill organisms with stages resistant to hypoxia. Although other ballast water treatment options may be more comprehensively effective, they come at greater environmental and financial cost. For instance, biocides may be hazardous for the crew as well as for native organisms in the vicinity of the ballast discharge. Moreover, these techniques come at a significant price for ship owners.

In contrast, we propose that widespread voluntary adoption of nitrogen treatment may result if the economic benefits for controlling corrosion become well known. Ballast water deoxygenation certainly deserves further exploration as a potential high priority treatment option, at least until international legislation mandates total mortality of ballast water organisms. While ballast water treatment has been controversial, raising conflicts between environmentalists and industry, nitrogen treatment represents a working solution that should appeal to both parties.

– Mario N. Tamburri1, Kerstin Wasson2, and Masayasu Matsuda3
1Monterey Bay Aquarium Research Institute and Monterey Bay National
Marine Sanctuary
2Elkhorn Slough National Estuarine Research Reserve
3Sumitomo Heavy Industries, Ltd.

A New Invasive Species: Undaria pinnatifida

In May 2001 Monterey Bay National Marine Sanctuary staff alerted divers and other coastal users to be on the lookout for the golden brown kelp Undaria pinnatifida. This notorious seaweed is native to the west coast of Japan but has been introduced into Australian, New Zealand, and European waters. Unfortunately, Undaria has now also shown up on the California coastline. Although it isn’t known how this invasive kelp got to the west coast of the United States, the species does appear to be spreading from southern California northward. Only two months after the Sanctuary issued the alert, John Hunt, a graduate student from Hopkins Marine Station, found several mature individuals of this new invader in Monterey Harbor.

Undaria pinnatifida, a seaweed native to Japan, has the potential of becoming a major pest in the Sanctuary. photo John Hunt

Commonly known as Wakame in Japan, Undaria is extensively cultivated as a fresh and dried food plant. However, in our coastal waters it has the potential of becoming a major pest: a single plant can release up to 100 million spores a day that can colonize both hard bottom surfaces as well as floating objects such as sea grass blades, ropes, ship and boat hulls, and pier pylons. An annual kelp, it can grow quickly—up to one centimeter a day—and at only fifty days old is mature enough to reproduce. Like other weeds, it thrives in disturbed habitats, often outcompeting and overgrowing native species. Long-term effects on the marine environment are not completely known, but elsewhere in areas of mass infestation by this kelp, marine ecosystems have completely changed.

A mature Undaria grows up to two meters in length and has a distinctive, spiraled (frilly), spore-producing structure at its base. It also has an obvious central stem or midrib to ten centimeters wide that extends for the length of the plant. The blade may be up to one meter wide and extends from the tip of the plant for half to three-quarters the length of the plant. Undaria is commonly found in sheltered harbor waters on rocks, breakwaters, and marine debris from the low-tide mark to fifteen meters.

Please report possible sightings of Undaria to the Monterey Bay National Marine Sanctuary at (831) 647-4206.

– Liz Love1 and Mario Tamburri1, 2
1Monterey Bay National Marine Sanctuary
2Monterey Bay Aquarium Research Institute