No free rides! (for aquatic organisms in ballast water)

3 04 2012

Ballast water being pumped out at sea.

The Coast Guard has released new rules for the treatment of ships’ ballast water in an effort to safeguard our aquatic ecosystems. The regulations have been in the works for over a decade, and aim to reduce introductions of non-native, and potentially invasive species along our marine coastlines as well as in the Great Lakes. Ballast water is suspected to have introduced some of the most notorious alien invaders such as the zebra mussel and the Asian shore crab. These species, facing no natural predators in their new digs, can drive native organisms to the brink of extinction and lead to plummeting biodiversity.

Not every non-native species will spread and outcompete its native cousins, but we don’t have a way of knowing which creatures will turn out to be bad actors. Compounding this uncertainty is the stealthy way that these animals and plants make their way into our waters. One might think that simple visual inspection of ballast water would detect something as obvious as a crab or a mussel stuck to the ballast tank wall, and it’s true: the adult forms of many of these organisms are readily detected. Unfortunately, most of these hitchhikers are sucked up into the ballast tanks as free-swimming larval forms–just one more tiny member of the planktonic community. Carried across the ocean, these tiny larvae are released into their new homes when ships discharge their ballast water upon arriving in port.

Intruder alert! Asian shore crabs are believed to have arrived in our waters via ballast water.

Ballast water is necessary for ships to maintain balance and the right buoyancy, so the Coast Guard has been working within that constraint on how to minimize the risk of invasive species introductions. Up to now, the only feasible solution was ballast water exchange (BWE) where ships take up ballast water in port, but then discharge it while underway and exchange it for water from the open ocean. The theory here being that coastal organisms will generally not survive when dumped in deep water, and in turn, any plankton picked up in the open ocean will be ill-suited to life in the nearshore environment of the ship’s destination. The trouble has been getting ships to practice BWE, which has been a voluntary procedure. BWE isn’t always practical or safe; since a ship discharging ballast water is not optimally stable, the exchange cannot be performed in rough seas or foul weather.

The new rules set forth by the Coast Guard require treatment of ballast water rather than simple exchange. Methods of treatment would include chemical means (biocides), filtration systems, or UV zappers to irradiate the water. Discharged ballast water will be required to contain less than a set maximum number of organisms per milliliter. These maximums have drawn criticism from environmental advocacy groups who recommend standards far more stringent. At present, the Coast Guard has stated that it will pursue further research into the achievability of such standards based on current or developing treatment technology, as well as the feasibility of detecting such low levels of organisms given current testing capabilities. Undoubtedly, the shipping lobby will vehemently oppose requirements for more refined and powerful systems once they have invested in currently available technology, so the environmental groups’ point is well taken: the standard set now is likely to be the standard we live with for years hence. Here’s hoping it’s substantial enough to make a difference.

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