Bacteria that exhale toxic gases have begun to flourish on the ocean floor along the Oregon coast where they are among the few life forms that can survive the suffocating waters of a long-lasting "dead zone," ocean researchers say.
Although such microbes are common in the deep ocean where waters typically hold little oxygen, scientists at Oregon State University cannot recall them blooming so strikingly in shallower waters closer to the shore.
But oxygen-starved water pooled near the coast appears to be giving them a new foothold.
Researchers last week revisited an offshore reef near Cape Perpetua, just south of Yachats, with a remote-controlled submarine that scans the sea floor with a video camera. It's the same site where they found legions of dead crabs and no fish earlier in August.
This time, the scientists found that even some tougher sea life that was hanging on when they first looked had died. Stately white sea anemones that usually stand about a foot tall were slumped over, said Francis Chan, a marine ecologist at Oregon State University.
"It looks like this has been so low oxygen for so long, some of what we thought were the hardier things are now succumbing," he said.
A ghostly white mat of what the scientists think are sulfur-eating bacteria had spread like patchy snowfall across the bottom. The bacteria are probably consuming hydrogen sulfide, a poisonous gas, given off by other microbes multiplying in the low-oxygen waters.
The new troupe of microbes takes over when oxygen runs out, Chan said.
"Now it's changing the system in some pretty basic ways," he said.
Low oxygen water has always been a key ingredient in Oregon's rich marine environment because it wells up from the deep each summer, bringing essential nutrients with it. That has long left some areas low in oxygen. The difference this year is that the oxygen-starved waters have pushed closer to shore, scientists say, pooling in blankets on the ocean bottom.
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At the same time, tiny marine organisms fed by the nutrients die, and their decay draws more oxygen out of the water. Oxygen levels have dropped to the lowest point scientists have seen in about 50 years of regular measurements along the Oregon coast, Chan said. Low-oxygen waters also have extended into waters off Washington, although less monitoring takes place there. |
The conditions seem to be easing near Lincoln Beach, on the north end of the zone scientists have been watching in Oregon. Oxygen concentrations are still low but have crept closer to normal levels the past few weeks.
Bottom-dwelling rockfish tagged by researchers remain in the general area, said Hal Weeks, a marine ecologist with the Oregon Department of Fish and Wildlife.
But oxygen levels remain very low in the latest readings near Cape Perpetua, where dead sea life and mats of bacteria were seen, Chan said. Shelves on the ocean floor shield Cape Perpetua from currents that might sweep new water in.
"It seems to have developed and expanded between the two times we looked," Weeks said.
They inspected only a section of sea floor, so it's not clear how widely the bacteria have spread.
Their next step is to try to measure toxic hydrogen sulfide gas in the water. It's such a rare phenomenon that they had to order new equipment to take readings.
"We don't have this in stock because we never had this happen before," Chan said.
Although marine life in deep ocean has adapted to lower oxygen and bacteria, that's probably not as true for organisms living in shallower waters closer to shore. The toxic gases may be another insult to any marine life still living nearby, Chan said.
"We don't think there are many animals in the sediment anymore that are still alive," he said. "It's sort of this downward spiral."
Michael Milstein: 503-294-7689; michaelmilstein@news.oregonian.com