The massive oil slick spreading across the Persian Gulf is not invading pristine territory but could deal a devastating blow to an important link in the food chain for marine life.

Richard Criddle, a biochemist and professor of biophysics at the University of California Davis, said the slick is now moving away from the most sensitive "nursery" area in the north end of the gulf where the bacteria, small worms and other essentials on the bottom of the gulf's food chain thrive.A shift in the winds, which will likely come as the weather turns toward summer but could happen at any time, could change the slick's course and drive it into the area where simple life forms already survive in hostile conditions, said Criddle, who is currently conducting laboratory research at Brigham Young University during a sabbatical leave that ends in June.

Commercial fishing operations extract shrimp and several varieties of fish from the gulf, which is also home to dolphins, five varieties of sea snakes and other larger marine life that, at some point, become dependent on the smaller plants and animals directly threatened by the spilled oil.

Criddle began studying marine life in the gulf during an 18-month stay eight years ago. He has spent at least one month in the gulf each year since then filming documentaries, mapping the location of unique coral formations and making possibly the only comprehensive evaluation of the gulf's marine conditions and narrow range of marine life.

He was ready to return to Kuwait to continue his research when the Aug. 2 Iraqi invasion thwarted his plans and left little hope for the survival of his Kuwaiti research partner. For the time being, all of Criddle's travel plans to the gulf are off.

Criddle identifies several factors that make the gulf a hostile environment for marine life. The entire body of water is twice as salty as the ocean because of the limited inflow of fresh water, high evaporation rate and restricted exchange with water from the open sea. The water temperature also fluctuates greatly with the season, and tides that sometimes advance and retreat across one or two miles of mud or sand in the shallow body of water continually stir up silt to make the water murky.

Those conditions reduce the range of marine life that can survive, which means life forms at the edge of existence are easily threatened by any new hazard.

Enter the oil slick.

Certain bacteria thrive on oil and will be multiplying rapidly as they gobble away at the slick, Criddle said. But lighter elements of crude oil quickly evaporate and make the spilled oil less like gasoline and more like tar. The thickening oil is harder for the bacteria to break down, and there isn't enough bacteria to sufficiently tackle the oil before thickening balls begin gradually sinking to the bottom where they roll around in the sand or mud until they collide with and coat rocks and coral formations Criddle describes as the underwater "pockets of life."

The bacteria still chip away at the oil, but the process takes hundreds of years.

Oil coming in contact with the shore is also likely to leave mud flats covered with an asphaltlike tar in areas where the gulf is so shallow that the water can retreat as far as two miles at low tide.

The slick that started this week with Iraq's destruction of Kuwaiti oil refineries and platforms is not the first war-related spill to damage the gulf. Other significant spills occurred during the eight-year war between Iran and Iraq, and the effects of those spills are still visible in certain areas of the gulf, Criddle said.