|
Posted by on July 22, 2005 at 17:35:46:
SAN FRANCISCO - Marine biologists are spotting ominous signs all along the Pacific Coast this year: higher nearshore ocean temperatures, plummeting catches of groundfish, an explosion of dead birds on coastal beaches, and perhaps most disturbing, very few plankton - the tiny critters that form the basis of the ocean's intricate food web. From California to British Columbia, unusual weather patterns have disrupted the marine ecosystem, scientists say. The normal northerly winds failed to show up this year, preventing the usual upwelling of colder water that sustains the plankton, and in turn, many other species from anchovies to cormorants to whales. Is this just a strange year, or is this what global warming looks like? Few scientists are willing to blame the plankton collapse on the worldwide rise in temperatures attributed to carbon dioxide and other gases believed to trap heat in the earth's atmosphere. Yet few are willing to rule it out. If these patterns continue, it could show that something in the atmosphere - and the Pacific Ocean - has permanently changed, with serious consequences for coastal birds, fish and marine mammals. "These natural changes can teach us a lot about what might happen if global warming came along," said Francisco Chavez, an oceanographer at the Monterey Bay Aquarium Research Institute. "That global change is going to affect the ocean is a given. We just don't know how or what the effects will be." It may be just an unusual year. Similar ecological signs have appeared during El Nino years, when increased sea surface temperatures in the equatorial Pacific alter weather patterns worldwide. But scientists say the West Coast hasn't had El Nino conditions this year. "There are strange things happening, but we don't really understand how all the pieces fit together," said Jane Lubchenco, a zoologist and climate change expert at Oregon State University. "It's hard to say whether any single event is just an anomaly or a real indication of something serious happening." The Pacific Coast ecosystem depends on winds blowing south along the coast to push warmer surface waters away from shore. This allows colder, nutrient-rich water from the ocean bottom to rise and feed massive blooms of phytoplankton, which are eaten by zooplankton including krill, the staple of many larger species, from sardines to whales. This year, the winds have been unusually weak, failing to generate much upwelling. As a result, nearshore waters are 5 to 7 degrees higher than normal and Oregon's coastal waters have only produced about one-fourth the total mass of phytoplankton generated in most years, said Bill Peterson, an oceanographer with the National Oceanic and Atmospheric Administration in Newport, Ore. "There are just a lot fewer of them, and that problem works its way up the food chain," Peterson said. "We're a little concerned because we haven't seen this before, so we can't predict when it's going to go away." Also, researchers are spotting warm-water fish much closer to shore, as well as subtropical plankton species rarely seen so far north, Peterson said. Seabirds are clearly distressed. On the Farallon Islands west of San Francisco, researchers this spring noted a steep decrease in nesting cormorants as well as a 90 percent drop in Cassin's auklets - the worst in more than 35 years of monitoring. The relatively rare birds, which feed mostly on krill, have since returned, but came too late for successful breeding this year, said Jaime Jahnke, a researcher with the Point Reyes Bird Observatory. "We don't know what's going on," Jahnke said. "If this is the result of some kind of large climate phenomenon that we don't know about, it's important to document it and understand what's causing it." On Washington state's Tatoosh Island, common murres - a species so sensitive to disruptions that scientists consider it a harbinger of ecological change - started breeding nearly a month late. It was the longest delay recorded in 15 years of monitoring, said Julia Parrish, a seabird ecologist at the University of Washington, Seattle. More disturbingly, researchers have reported a sharp increase in dead birds washing up on the shores of California, Oregon and Washington. Along Monterey Bay in Central California, there are four times as many dead birds such as Cassin's auklets, common murres and Brandt's cormorants than in most years, said Hannah Nevins, a marine scientist at Moss Landing Marine Laboratories. "Basically, they're not finding enough food, and they use up the energy that's stored in their muscles, liver and body fat," Nevins said. "It's a level of mortality that's significantly above our long-term average over the last seven years." On the Oregon and Washington coasts, volunteers found one dead Brandt's cormorant every 1.3 kilometers, compared with every 50 kilometers in most years, and logged a sixfold increase in common murre mortality, Parrish said. "The bottom has fallen out of the coastal food chain, and there's just not enough food out there," Parrish said. "We're seeing these stress signals. (The birds) are delaying breeding, they're abandoning their colonies and they're washing up on beaches. They're basically dying. They're way stressed out." Fish appear to be feeling the effects, too. NOAA surveys show a 20 percent to 30 percent drop in juvenile salmon off the coasts of Oregon, Washington and British Columbia this June and July, compared with the average count over the previous six years. And researchers counted the lowest number of juvenile rockfish in more than 20 years of monitoring in Central and Northern California - fewer than 100 caught between San Luis Obispo and Fort Bragg this year, compared with "several thousand" last year, said National Marine Fisheries Service biologist Keith Sakuma. "This year was the worst year ever because the rockfish depend on the upwelling," Sakuma said. Most scientists are reluctant to ascribe this year's weak northerly winds to global warming. Climate change is believed to be a gradual process, and what's happening this year is relatively sudden. Scientists also differ on whether global warming will increase or decrease the intensity of such winds. Whatever the cause, it may be related to a weather pattern that brought record rainfalls to California and unusually dry, warm weather to the Pacific Northwest, said Nathan Mantua, a climate expert at the University of Washington, Seattle. It's too soon to draw conclusions. Scientists can do little more than take notes, and wait. "To me, it really points out how uncertain our speculation is about global warming's impact on these upwelling systems," Mantua said. "If we did see this next year, the notion that global warming plays a role in this carries more weight."
| 
