Video. Biologists told ABC News that the entire food chain had been disrupted -- partly from the mass of oil and partly because the oil has sapped the water of oxygen. "What we're really witnessing may be a shift in the whole ecosystem feeding structure, the food web," said Bob Shipp, director of marine biology at the University of Southern Alabama. "It also may be altered permanently -- as we've seen in other parts of the world where these things happen." The oil spill has disturbed plant life too. Algae cannot survive if there isn't enough oxygen in the water, and a loss of algae could damage the ecosystem and the fisheries that rely on marine life. Evidence of marine biologists' doomsday scenario thrashes in the Gulf waters as sharks crowd into shallow waters.