Representatives of an environmental coalition and a marine-biology researcher Thursday called on the Seattle City Council to ban plastic bags as a way to protect Puget Sound marine life.

City Councilmember Mike O'Brien is expected to introduce an ordinance Monday to ban single-use plastic shopping bags. The bill is modeled on one adopted earlier this year by Bellingham that had widespread community support as well as backing from the city's two largest grocery chains.

The Seattle bill would ban plastic checkout bags and charge customers 5 cents for each paper grocery bag as a way to remind shoppers to bring reusable bags and to reimburse stores for the greater cost of paper bags.

Thursday's news conference was at Victor Steinbrueck Park at the north end of Pike Place Market with a sweeping view of Puget Sound as backdrop.

Julie Masura, a faculty member at the University of Washington Tacoma's Center for Urban Waters, said every water sample she has taken from Puget Sound over the past year-and-a-half has contained small bits of plastic.

While researchers haven't found a direct link between those bits — known as microplastics — and harm to marine life, Masura said they do know that larger pieces are being ingested and "clogging the guts" of some marine animals and birds.

Environment Washington estimates Seattle uses 292 million plastic bags a year. Only 6 percent are recycled nationally, said the group's Katrina Rosen.

"We need to seriously reduce the amount of plastic entering Puget Sound," Rosen said.

Environment Washington, the Surfrider Foundation, People for Puget Sound and the Sierra Club have gathered about 1,400 signatures calling on the City Council to ban plastic bags.

"The plastic bags we get at the grocery store seem free, but they have an enormous cost to the environment," said Jody Kennedy, spokeswoman for Surfrider Foundation, which promotes protection of oceans, waves and beaches around the world.

In 2009, Seattle residents rejected a 20-cent fee on paper and plastic bags that had been approved by the City Council. The plastics industry spent $1.4 million to help defeat the fee.

Lynn Thompson: 206-464-8305 or lthompson@seattletimes.com. On Twitter @lthompsontimes.