PORTLAND – Sen. Susan Collins is among a group of lawmakers that plans to introduce a bill that would increase safeguards against invasive species.

The bill would require ships entering U.S. ports to sanitize ballast-water tanks that can carry organisms.

“In all likelihood, the Asian shore crab was carried to the East Coast of the United States in the ballast water of ships, allowing it to spread to Maine just two years ago,” Collins, R-Maine, said in a statement. “We need to adopt strong ballast-water standards in order to stop giving species like this a free ride across the ocean.”

Asian shore crabs were believed to be carried in ballast water to the mid-Atlantic coast. They were first spotted in 1988 in New Jersey.

Some fear that the crab will hurt shellfish and possibly juvenile lobsters.

Another invader, the European green crab, reached Maine’s coast in the 1950s and devoured the soft-shell clam industry. The crab still cost an estimated $44 million a year in damage and control efforts in the United States.

Ballast water provides an empty ship with extra stability before it leaves a port. The sea water is emptied before cargo from another port is loaded onto the ship. Modern cargo ships can carry between 100,000 and 10 million gallons of ballast water.

Most ships coming into Portland Harbor do not discharge ballast water because they are carrying full loads of cargo. But Maine is within easy range of some species that disembark at other East Coast ports.

“Once something comes to this side of the Atlantic, it’s inevitable that it’ll get dispersed over time and settle in where the environmental conditions will let it survive,” said John Sowles, ecologist with the Maine Department of Marine Resources.

Collins and Sen. Carl Levin, D-Mich., plan to introduce legislation Wednesday that would require ships built after 2006 to have treatment systems before entering U.S. waters. The bill would require ships built before 2006 to install treatment systems by 2011.

Researchers are still developing mechanical, chemical and radiation treatment systems, and none have yet been proved safe and effective. Federal and international rules now encourage ships to empty ballast water in the open ocean, where organisms that hitched a ride are less likely to survive.

The International Maritime Organization is considering a requirement that ships built after 2018 be equipped to treat ballast water, Collins said, and the United States needs to adopt stricter standards to force the international shipping community to take more aggressive action.