ALIEN INVADERS

An article posted on the Maine Department of Marine Resources Web site last year notes that the Asian shore crab, inadvertently introduced to this country in 1988, had spread from North Carolina to Portland, but its ability to thrive in the colder water to the north was uncertain. Now, ending that uncertainty, the crab has been found in Penobscot Bay.

This is no reflection on DMR -its reports always are current and thorough, its Web site is among the most informative at any level of government. This is a reflection, however, on the persistence, propagation powers and appetite of this new and worrisome alien invader.

Also called the Japanese shore crab, this tiny critter (about the size of a silver dollar) has the potential to be the perfect invasive species. It reproduces like mad, up to three times a year. It has no natural predators and is extremely aggressive – the way it dismembers and devours the larger green crab (an invader of a century ago) is one of the more violent scenes to be found in the tidal zone. Its small size precludes any commercial value. It eats virtually anything, but is particularly fond of species with commercial value, such as clams and mussels. There is no evidence yet that it eats lobster larvae, but that more likely is due to lack of research than dietary preference. It already is the dominant species on beaches from New Jersey to Connecticut. Further, it can tolerate low salinity, making a march up Maine’s coastal estuaries entirely possible.

Scientists believe this native of the western Pacific got to these shores the same way so many damaging species move across the globe: in the discharged ballast water of cargo vessels. Scientists also believe this crab could be the most damaging invader since the zebra mussel, the freshwater European species that choked the Great Lakes and central U.S. rivers, devoured the food needed by native species and even crippled power plants, dams and water systems, causing an estimated $5 billion in damage.

World governments have been aware of the dangers of ballast-water discharges for decades but have been painfully slow to act. The International Maritime Organization in 1991 adopted voluntary guidelines for the exchange of ballast water in the open ocean, where hitchhiking coastal species are unlikely to survive, but ratification of mandatory rules is years away. The U.S. Invasive Species Act of 1996, passed in reaction to the zebra mussel debacle, relies on open-ocean exchange as prevention, but waivers for safety and stability of the vessel and inapplicability for coastal shipping leave gaps that only a comprehensive program can fill. Research continues into such techniques as irradiation, ultrasound and heat to treat ballast water, but implementation may take a decade or more.

Congress now is in the process of reauthorizing the Invasive Species Act and there is considerable interest to increase funding for research to solve the ballast-water problem. Meanwhile, Maine beachgoers are asked to keep an eye peeled – key features are a small hard bubble at the crux of the crab’s claws, three spines along the shell (there’s five on a green crab) and light-and-dark banding on the legs – and to report sightings to DMR. Crushing the little rascal underfoot is optional.