Low Oxygen Dead Zone off Oregon Coast Worst Ever

CORVALLIS, Oregon, August 10, 2006 (ENS) - Parts of the seafloor off Oregon are carpeted with dead Dungeness crabs and rotting sea worms, and virtually all of the fish appear to have fled the area. New research attributes the dead zone to the worst low oxygen ocean conditions ever observed on the west coast of the United States.

Looking for an end to this dead zone, researchers at Oregon State University, OSU, instead found even more extreme drops in oxygen along the seafloor. Levels of dissolved oxygen are near zero in some places.

"We saw a crab graveyard and no fish the entire day," said Dr. Jane Lubchenco, the Valley Professor of Marine Biology at OSU. "Thousands and thousands of dead crab and molts were littering the ocean floor, many sea stars were dead, and the fish have either left the area or have died and been washed away.

"Seeing so much carnage on the video screens was shocking and depressing," she said.

Dr. Jane Lubchenco professor of biology and zoology at Oregon State University, is a past president of the American Association for the Advancement of Science. (Photo courtesy OSU)

OSU scientists with the Partnership for Interdisciplinary Studies of Coastal Oceans, PISCO, in collaboration with the Oregon Department of Fish and Wildlife, used a remotely operated underwater vehicle this week to document the magnitude of the biological impacts and continue oxygen sampling.

Oregon's dead zone was first identified in 2002 - this most recent low-oxygen event began about a month ago.

Any level of dissolved oxygen below 1.4 milliliters per liter is considered too low for most marine life to survive.

In the latest findings from one area off Cape Perpetua on the central Oregon coast, surveys showed 0.5 milliliters per liter in 45 feet of water; 0.08 in 90 feet; and 0.14 at 150 feet depth.

These are levels 10 to 30 times lower than normal.

In one extreme measurement, the oxygen level was 0.05, or close to zero. Oxygen levels that low have never before been measured off the U.S. West Coast.

"Some of the worst conditions are now approaching what we call anoxia, or the absence of oxygen," said Francis Chan, a marine ecologist with OSU and PISCO. "This can lead to a whole different set of chemical reactions, things like the production of hydrogen sulfide, a toxic gas. It's hard to tell just how much mortality, year after year, these systems are going to be able to take."

Researchers from OSU, PISCO and other state and federal agencies are developing a better understanding of how these dead zone events can occur on a local basis. But it is still unclear why the problem has become an annual event.

"When you see the same thing happening with this regularity, it suggests that something is fundamentally different," said Lubchenco. "This is a significant departure from normal conditions and you have to wonder what's going on. This ocean system has changed, and we're paying attention."

One of the areas sampled is a rocky reef not far from Yachats, Oregon. Ordinarily this is prime rockfish habitat, inhabited by black rockfish, ling cod, kelp greenling, and canary rockfish. The seafloor hosts large populations of Dungeness crab, sea stars, sea anemones and other marine life.

This week, it is covered in dead and rotting crabs, the fish are gone, and worms that ordinarily burrow into the soft sediments have died and are floating on the bottom.

The water just off the bottom is filled with a massive amount of what researchers call "marine snow" – fragments of dead pieces of marine life, mostly jellyfish and other invertebrates. As this dead material decays, it is colonized by bacteria that further suck any remaining oxygen out of the water.

"We can't be sure what happened to all the fish, but it's clear they are gone," Lubchenco said. "We are receiving anecdotal reports of rockfish in very shallow waters where they ordinarily are not found. It's likely those areas have higher oxygen levels."

Scientists have been monitoring dead zones off the Oregon coast for five years. In this 2004 photo, Chris Holmes and Francis Chan, members of the Partnership for Interdisciplinary Study of Coastal Oceans, bring up a sample. (Photo courtesy OSU)

Scientists observed similar but not identical problems in other areas. Some had fewer dead crabs, but still no fish. In one area off Waldport, Oregon, usually known for good fishing and crabbing, there were no fish and almost no live crabs.

The exact geographic scope of the problem is unknown, but this year for the first time it has also been observed in waters off the Washington coast as well as Oregon. Scientists say the dead zone has very likely affected marine life in areas beyond those they have actually documented.

This is the fifth year in a row a dead zone has developed off the Oregon Coast, but none of the previous events were of this magnitude.

The researchers say these hypoxic events are connected to upwelling - the movement of cold, nutrient rich water to the surface near the ocean shore.

Normally, upwelling is valuable - the nutrients it brings up are critical for much marine life and key to productive fisheries. But in the hypoxic events, the upwelled water is coming from the sub-Arctic, and is even colder, more nutrient rich and lower in oxygen than usual.

"Hypoxic conditions such as this have been documented in other nearshore upwelling ocean regions of the world," said Jack Barth, a professor of oceanography at OSU, "but never on the central Oregon coast."

Earlier this year, strong upwelling winds allowed a low oxygen pool of deep water to build up. That pool has now come closer to shore and is suffocating marine life on a massive scale.

Ordinarily, north winds drive ocean currents that provide nutrients to the productive food webs and fisheries of the Pacific Northwest. These crucial currents can also carry naturally low oxygen waters shoreward, setting the stage for dead zone events.

Some strong southerly winds might help push the low oxygen water further out to sea and reduce the biological impacts, Lubchenco said. But the current weather forecast predicts that the opposite will occur.

Changes in wind patterns can disrupt the balance between productive food webs and dead zones, but researchers say this breakdown does not appear to be linked to ocean cycles such as El Niño or the Pacific Decadal Oscillation.

Extreme and unusual fluctuations in wind patterns and ocean currents are consistent with the predicted impacts of some global climate change models, scientists say, but they cannot yet directly link these events to climate change or global warming.