WASHINGTON, March 4— Warming seas have wiped out most of a critical link in the ocean food chain in the waters off Southern California, creating a vast wasteland with few fish and few birds, researchers have reported.
In a study published on Friday in the journal Science, Dr. John McGowan of the Scripps Institution of Oceanography in San Diego reported that the water temperature off San Diego had risen two to three degrees Fahrenheit since 1951 and that the population of zooplankton, a critical part of the food chain, had declined by 80 percent.
Zooplankton comprises the tiny ocean creatures that are the primary food for hundreds of fish and bird species. Without them, once-teeming waters become almost void of life, Dr. McGowan said, adding, "It already is pretty dead out there."
Dr. McGowan recalled an abundance of fish and bird life on scientific cruises in the 1960's and said that on a recent cruise he "was flabbergasted at the difference."
Dr. McGowan and Dr. Dean Roemmich, another Scripps scientist, reported on the results of hundreds of thousands of water, temperature and plankton samples taken during 222 scientific cruises over the last 42 years.
The cruises covered the same sampling sites within a 50,000-square-mile area off San Diego and Point Conception, Calif. During the period, Dr. McGowan said, there had been an increase in the temperature in the top 600 feet of water and a decline in the zooplankton.
"Zooplankton is the main diet for many species of fish, including sardines, anchovy, hake, jack mackerel and Pacific mackerel," Dr. McGowan said. "This could have a very strong effect" on fish survival.
The rise in temperature, he said, was robbing surface waters of nutrients like nitrates and phosphates that the plant plankton needs to survive. Because the zooplankton feeds on the plant plankton, the loss of nutrients ripples up the food chain.
Dr. McGowan said there was no way to determine whether the warming resulted from natural changes or the greenhouse effect, in which heat from the Sun is trapped by various atmospheric pollutants like carbon dioxide from the burning of fossil fuels and nitrous oxide from motor vehicles.
Commercial anchovy fishing in the area has already crashed, Dr. McGowan said, and the commercial fish harvest for other species has declined by about 40 percent since the 1970's.
Dr. Dick Veit, a zoologist at the University of Washington, said the findings were consistent with other studies that had shown stunning losses of fish and sea bird populations along the Pacific Coast.
Dr. Veit said that he had found a decline of 90 percent in the numbers of one group of sea birds and that other researchers had reported similar disappearances of sea life along the West Coast.