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Although most microbes that are moved about the world in the ballast water of ships are unlikely to pose health or economic threats, dangerous aquatic microbial invasions are possible and a case can be made for stringent new ballast-water management standards, says an article written by two oceanographers from Old Dominion University and Nova Southeastern University in Florida.

Fred Dobbs, associate professor in ODU's Ocean, Earth and Atmospheric Sciences Department, and Andrew Rogerson, professor and associate dean of the Oceanography Center at Nova Southeastern, are authors of the cover article in the June 15 edition of Environmental Science and Technology magazine. The article text is available online at http://pubs.acs.org/journals/esthag/index_magazine.html. Their title is: "Ridding Ships' Ballast Water of Microorganisms: Is it even possible to remove, kill or inactivate all of them-and, if so, should we try?"

The microbes they identify as most dangerous include toxic dinoflagellates that can devastate aquaculture and adversely affect natural populations, including marine mammals, and cause paralytic shellfish poisoning in humans. They also warn of potential health problems caused by the bacterium Vibrio cholerae, which causes human cholera.

The article appears at a time when world trade is increasing, resulting in more international ship traffic and more opportunities for ballast water introduction of harmful species. A recent National Geographic documentary telecast on the Public Broadcasting System included commentary by invasion scientists and portrayed aquatic invasions as a growing threat. On the other hand, a few voices in the scientific community are downplaying the long-term dangers of species invasions. In addition, one hypothesis questions whether microbial invasions are even possible. The cover article in May's Discover magazine brought a storm of protest from scientists and environmentalists by suggesting that the invasive species scare is overblown.

"I think our article is more cautious about invasions," said Dobbs, who is a marine microbial ecologist, in response to a question about the Discover article. "We make the point that most documented aquatic invasions have been those of (larger) invertebrates. The only case for which we think there is strong evidence for a microbial invasion is that of red-tide dinoflagellates in Australia. We make a second point, however, that it would be simplistic and possibly very wrong to consider aquatic microbial invasions do not occur or could not be mediated by ballast water."

Ships take on and dump ballast water as needed for stability, often to offset either the loading or offloading of cargo. The process moves water-and organisms in the water-from one port to another. Harmful invasions may happen when a species finds a new environment where it has no natural predators, a reduced parasite load, or other conditions that help it flourish.

Many ships try to minimize potential harm by dumping or exchanging ballast water in high-salinity open waters-which are not as likely as coastal waters to enable an invasion or to contain potentially invasive species.

Ballast water management proposals of the International Maritime Organization, which are now being considered for ratification by IMO member nations, could force ships to have on-board treatment systems that would greatly reduce the number of microbes that are discharged. The authors write that proposed IMO standards should go far toward minimizing risks, but warn that research underway now may show that more stringent measures are needed.

Environmentalists have rallied behind the National Aquatic Invasive Species Act of 2005, which is before Congress, but may stall like a similar bill did last session. Some states bordering the Great Lakes, which have been hard hit by invasive species, have decided to impose piecemeal regulations. Michigan lawmakers, this spring, approved a law that will require oceangoing ships entering ports there to prove they are equipped to treat any ballast water they have on board. Also this spring, a federal judge in California ruled that the Environmental Protection Agency must begin regulating ballast water by permit under the Clean Water Act, although the specific implementation of the ruling is still undecided.

Although the authors believe present ballast water treatment technologies cannot totally eliminate all microbes, they do not see this necessarily as a matter of great concern. It seems to be sufficient in most instances, they say, to have on-board treatment or combination of treatments-exposure to ultraviolet light and chemical biocides are two-that eliminate most microbes. The diminished numbers of live microbes that are dumped after treatment are likely to be kept in check by predators, the sun's UV rays or other inhibiting conditions.

The authors also acknowledge a recent hypothesis that the distribution of free-living microbes is globally ubiquitous, which means they are essentially everywhere and do not have a homeport, so to speak. This would make it impossible for them to be an invasive species and their presence in ships' ballast water would be of greatly reduced concern. The authors believe the hypothesis is worthy of more research.

Almost all harmful invasions blamed on ballast water dumping, the article notes, have been of larger invertebrates such as the Eurasian zebra mussel, which has brought about profound ecological change in the Great Lakes region since being introduced to North America in the 1980s. In the Chesapeake Bay, shellfisheries are threatened today by the Rapa whelk, apparently introduced by ballast water in the late 1980s or early 1990s from the Sea of Japan or the Black Sea.

The near absence of headline-grabbing microbal invasions might suggest that few will happen in the future, but Dobbs and Rogerson give reasons for caution.

Dinoflagellates' cyst stage affords them a resilience that makes them well suited to survive transport by ships and discharge during deballasting, according to the article. Indeed, the sudden, well-documented appearance of a red-tide dinoflagellate in southern Australian waters has been attributed to its dispersal by ballast-water operations.

The dinoflagellates Pfiesteria, which are microscopic single-cell algae, have been blamed by some researchers for fish kills on the East Coast in the 1990s. Dobbs said scientists at the University of North Carolina at Greensboro have found Pfiesteria broadly distributed around the world, although typically of low genetic variability. "Is such low variability because of very recent dispersal-maybe via ballast water?" Dobbs asked. "It's a hypothesis my colleagues hope to pursue," he said.

The cholera bacterium, which is widely distributed worldwide but generally not virulent, may pose a special threat because it may exhibit a certain type of gene transfer. Under a scenario explained by the authors, a ballast-water introduction of one variant of the species could boost antibiotic resistance, virulence, or both in indigenous cholera bacteria. If subsequent research shows that significant gene transfer can occur, then, the authors write, ballast water management "clearly should become more stringent and targeted at eliminating the discharge of living bacteria."

In conclusion, the authors propose that the threat posed by toxic dinoflagellates and Vibrio cholerae in ships' ballast water "presents a compelling argument for removing or killing microorganisms known to be problem groups, at least until the global-ubiquity debate has been resolved."

Dobbs' expertise in the field has kept him in demand this spring. He has given several newspaper and radio interviews about invasive species issues in the Great Lakes and the Chesapeake Bay, and has traveled and presented his work to a Coast Guard public hearing in Cleveland in May and to a workshop in Portland, Oregon, in June.

This article was posted on: June 20, 2005

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