Warming seas have wiped out most of a critical link in the ocean food chain in the waters off San Diego, creating a vast watery waste with few fish and few birds, researchers have reported.
In a study published today in the journal Science, John McGowan of the Scripps Institution of Oceanography at La Jolla reports that the water temperature off San Diego has climbed by two to three degrees Fahrenheit since 1951 and the population of zooplankton, a critical part of the food chain, has declined by 80 percent.The lack of zooplankton leaves little food for many fish and birds, causing the once-teeming waters to be almost void of life, McGowan said.
"It already is pretty dead out there," he said. The scientist said he remembers an abundance of fish and bird life on scientific cruises in the 1960s and that on a recent cruise "I was flabbergasted at the difference."
McGowan and Dean Roemmich, also of Scripps, reported on the results of hundreds of thousands of water, temperature and plankton samples taken during 222 scientific cruises over the past 42 years.
The cruises covered the same sampling sites within a 50,000-square-mile area off the coast of San Diego and Point Conception, Calif.
During the period, McGowan said there has been an increase in temperature in the top 600 feet of water and a drop in zooplankton, the tiny ocean creatures that are the primary food for hundreds of fish and bird species.
"Zooplankton is the main diet for many species of fish, including sardines, anchovy, hake, jack mackerel and Pacific mackerel," he said. "This could have a very strong effect on fish survivorship."
McGowan said the increased water temperature is robbing surface waters of the nutrients, such as nitrates and phosphates, the plant plankton need to survive. Since the zooplankton feed on the small plant plankton, the loss of nutrients sends a ripple up the entire food chain.
He said there is no way to determine whether the warming is being caused by industrial pollution in the atmosphere that is causing the greenhouse effect or natural change.
"If we can pin it down to the greenhouse effect, then we've really got something to worry about," he said.
Commercial anchovy fishing in the area already has crashed and the commercial fish harvest for other species has declined by about 40 percent since the 1970s, Mc-Gow-an said.
Dick Veit, a University of Washington zoologist, said the findings are consistent with other studies that have shown stunning losses of fish and seabird populations along the Pacific coast.
Veit said he has found a 90 percent decline in the numbers of one seabird and that other researchers have reported similar disappearances of sea life along the West coast.