Shellfish at risk: Puget Sound becoming acidified

The waters in Puget Sound's main basin are acidifying as fast as those along the Washington Coast, where wild oysters have not reproduced since 2005.

And in parts of Hood Canal, home to much of the region's shellfish industry, water-chemistry problems are significantly worse than the rest of Puget Sound.

Scientists from the University of Washington and the National Oceanic and Atmospheric Administration (NOAA) warned Monday that the changing pH of the seas is hitting Puget Sound harder and faster than many other marine waters.

That increasingly corrosive water — a byproduct of carbon-dioxide releases from industries, power plants and vehicles — is probably already harming shellfish, and over time it could reverberate through the marine food chain.

"We are concerned that ocean acidification may be contributing to the recent loss of oyster larvae reported by oyster hatcheries in the Pacific Northwest, including Puget Sound," UW scientist Jan Newton said.

Atmospheric carbon dioxide dissolves in seawater, producing acids that raise the water's corrosiveness. As seawater becomes more corrosive, it can kill fish eggs and essentially dissolve the shells of small crustaceans, baby shellfish, and other tiny creatures at the base of the food web. Among the hardest hit: oyster larvae.

Since the dawn of the industrial revolution, the pH of ocean surface waters has dropped about 30 percent, and is expected to drop far more over the next century.

But NOAA scientists a few years ago found marine waters off the Washington Coast were becoming more acidified far sooner than anyone expected. And because of the way marine water circulates in our part of the Pacific Ocean, waters were becoming even more corrosive closer to shore, where most sea creatures live.

Deep, cold water typically carries more carbon dioxide than most surface waters, but that water rises along the Pacific Northwest in "upwelling" events. That acidified water pushes into the Strait of Juan de Fuca and into Hood Canal and Puget Sound, where natural processes lower the pH even more.

In southern Hood Canal, for example, poor water circulation and nutrient-rich runoff from pollution and leaky septic tanks stimulate the growth of phytoplankton and other organic matter.

As the phytoplankton dies and sinks, it produces carbon dioxide, which starves the stagnant water of oxygen and lowers its pH. That has led to massive die-offs of fish, octopus, crab and other creatures in recent years. Acidification from greenhouse-gas emissions just compounds the problem.

On the pH scale, strongly alkaline materials such as oven cleaner measure about 13. Hydrochloric acid has a pH of 1. Seawater usually measures around 8.1.

In some places, the waters of Puget Sound measured 7.7, similar to some of the lowest measurements taken along the Washington Coast. Parts of Hood Canal were as low as 7.4

"The pH levels we saw there [Hood Canal] were far lower than anything we've seen in the open ocean," said oceanographer Richard Feely, with NOAA's Pacific Marine Environmental Laboratory in Seattle, the lead author of the new study.

Results were posted online Monday in the journal Estuarine, Coastal and Shelf Science.

Feely estimated that a quarter to a half of the increased corrosiveness in Hood Canal was due to man-made carbon dioxide dissolving in the water. That percentage could increase to more than 80 percent in coming decades.

Little field work has been done to directly tie any of Puget Sound's many ecological problems to acidifying waters. But scientists say there's strong evidence to suggest corrosive waters are already impacting oyster production. Wild oysters in Willapa Bay did not reproduce again in 2009, the sixth year in row.

The Taylor Shellfish hatchery on Hood Canal's Dabob Bay had its first good year in several in 2009, but company spokesman Bill Dewey said he suspects that's merely because the winds cooperated, preventing acidified seawater from entering the relatively stable bay.

The company recently installed sophisticated pH monitors at its hatchery to determine when it's best to draw water off the surface, from way down deep — or not at all.

Using similar instruments, operators of a hatchery in Oregon's Netarts Bay have improved oyster reproduction by only sucking in seawater in the afternoon, after photosynthetic organisms have bumped up the water's pH.

Scientists Monday said they will soon deploy the most sophisticated array of instruments in state history 15 miles off La Push to help gather more data about changing ocean conditions.

They urged Congress and others to find ways to immediately scale back carbon-dioxide emissions, but warned even if that happens soon, acidification will grow for years to come — a message the shellfish industry has already received.

"We know we've still got a lot of hurt coming our way," Dewey said.

Craig Welch: 206-464-2093 or cwelch@seattletimes.com.

Seattle Times science reporter Sandi Doughton contributed to this report.