PORTLAND – Researchers are scraping kelp and taking water samples near pilings of piers and floating docks this week to find out how many exotic marine species have invaded Maine’s coastal waters.

The team of 25 scientists is conducting the weeklong survey as part of a project to determine how prevalent such species have become in waters stretching from Maine’s Casco Bay to New York Harbor.

The group consists of experts with specialties from tiny crustaceans to colorful sea squirts. They hail from places as varied as England to Seattle to the Carolinas to Rhode Island.

European green crabs, Asian shore crabs, periwinkles and other nonnative species can spread from port to port through a ship’s ballast water.

While some species are benign, others can spread rapidly and cause widespread economic and ecological harm. The green crab, for example, preys on commercially valuable shellfish.

“One reason that we’ve chosen Portland is because, with all the ship traffic coming in and out of here, there’s a good chance that some of them may have come in on some of the ships,” said Jan Smith, director of the Massachusetts Bay’s National Estuary Program.

A similar survey three years ago in Massachusetts found that 10 percent of the species identified were not native to the state, including two species that had never been seen before on the East Coast.

In Maine, the survey began Monday with a visit to Port Harbor Marine in South Portland, then the group moved on to Portland Yacht Services on Fore Street. They spent the afternoon at Brewer’s South Freeport Marine.

At Portland Yacht Services, Niels Hobbs of the University of Rhode Island used a strainer and an eyedropper to capture tiny animals called arthropods and isopods, which are closely related to crabs and shrimp.

Gretchen and Charles Lambert of the University of Washington in Seattle are specialists in sea squirts.

“Of the many invasive animals, the most abundant one in this harbor is a sea squirt from Japan,” Charles Lambert said, pointing to an orange colony of squishy sea squirts on the dock.

Sea squirts, or tunicates, can smother shellfish fisheries and have caused millions of dollars of damage to mussel and oyster growers on Prince Edward Island, Gretchen Lambert said.

The scientists were brought to Maine by the Northeast National Estuary Program Partners, the Casco Bay Estuary Program and MIT Sea Grant, with the help of a $60,000 grant from the U.S. Environmental Protection Agency.