The heavy oil spilled into Galveston Bay showed signs Monday of harming one of the nation’s great natural nurseries, with biologists finding dozens of oiled birds on just one part of the Bolivar Peninsula.

Scientists found the birds on a wildlife refuge just two miles from where a partially sunken barge leaked as much as 168,000 gallons of thick bunker fuel oil after colliding with another vessel Saturday.

“We expect this to get much worse,” said Jessica Jubin, a spokeswoman for the Houston Audubon Society, which manages the Bolivar Flats preserve where the birds were found.

The concern comes as tens of thousands of birds are passing through the upper Texas coast on their annual flight north. But the worry also extends to the bay’s oyster reefs and the shrimp, crabs and fish that rely on the coastal marshes for shelter and food.

Scientists said that while the spill’s damage will be magnified by its awful timing, it could take years for a fuller picture of the ecological toll to emerge.

Galveston Bay was under stress from development, drought, pollution and storms. But its oil spills are typically small, averaging about 100 gallons per incident, according to an analysis by the Houston Advanced Research Center. The latest spill is the largest in the Ship Channel since a facility leaked 70,000 gallons of bunker fuel in 2000.

For now, the primary concern is the marshes, which have declined over decades because of sea-level rise, erosion and subsidence, a condition caused by sinking soil.

The intertidal wetlands are critical because they act as nature’s speed bumps against storm surges headed toward Houston. The marshes also filter water and serve as a productive nursery for a variety of sea life, from white and brown shrimp to blue crab and red drum.

Since the collision, crews have deployed more than 69,000 feet of boom to protect the marshes from the spill, officials said.

If oil reaches the marshes, the grasses that hold the land together will suffocate and die. Without the root system of the dead vegetation, the marshes will erode and vanish into the bay.

“We’ve lost so many of these marshes that they are less resilient than they once were,” said John Jacob, who leads the Houston-based Texas Coastal Watershed program for Texas A&M University. “So any spill can be impactful.”

Oiled birds found

The salt marshes at Bolivar Flats attract more than 100 species of birds, including the endangered piping plover, a small, sand-colored shorebird. As of Monday, no oil had reached the area, U.S. Coast Guard Capt. Brian Penoyer said.

The Houston Audubon Society, meanwhile, found 15 oiled birds in a small area of blustery beach the group surveyed at its Bolivar Flats sanctuary.

Many of the birds will not survive because they can swallow the oil and be poisoned when they try to remove it with their beaks. The oil also coats their feathers, destroying what keeps them warm and enables them to fly.

Small wading birds, such as the sanderling and ruddy turnstone, seem most affected; the American avocet and other long-legged birds can keep the oil away from their feathers, said Richard Gibbons, the Houston Audubon Society’s conservation director.

Across Galveston Bay, the Nature Conservancy reported no oil at its 2,300-acre Texas City preserve, which supports migratory birds and year-round waterfowl populations.

Laura Huffman, the Nature Conservancy’s Texas director, praised the state’s containment and cleanup efforts, but said the oil spill “couldn’t have come at a worse time because it is the high point of the migratory season.”

State lends a hand

The Texas Parks and Wildlife Department reported finding three dead birds while teams of biologists searched east Galveston Island, Pelican Island and the Bolivar Peninsula for creatures affected by the spill.

Meanwhile, the Texas General Land Office, which is responsible for the state’s shorelines, sent three teams to survey conditions where the land meets the water.

Angela Sunley, a state biologist, said her team found oily mats and tar balls while surveying six miles of Galveston’s East Beach by foot. The teams will conduct similar reviews over the next few days as part of a large effort to document the damage.

“We are trying to get a baseline,” said Toby Baker, a Gov. Rick Perry-appointed member of the Texas Commission on Environmental Quality, which is assisting the General Land Office with the work.

The process, known as the Natural Resources Damage Assessment, is the government’s primary tool to hold responsible parties accountable for the oil spill. Federal law requires the parties to cover the cleanup costs and a portion of the damage, but they can challenge the scientific findings in court.

The effort should be less complicated than the continuing assessment of the massive 2010 disaster in the Gulf of Mexico. The Galveston spill involved a fixed amount of oil; the Gulf tragedy went on for months after a deep-sea well ruptured.

The accounting can take five to eight years to complete and perhaps longer if challenged in court. For example, it took 15 years for Texas officials to resolve a dispute over damages from mercury contamination in Lavaca Bay.