A bloom of ocean algae that produces a toxic acid has sickened and killed hundreds of birds, sea lions and dolphins in California, environmentalists said. Domoic acid is produced by microscopic algae. Birds and sea mammals ingest the acid by eating fish and shellfish who dine on the algae. The algae population increases or "blooms" every year as the ocean waters warm but this year's bloom seems early, extensive and "very, very thick," said David Caron, who teaches in the biological sciences department at University of Southern California. "In five years of study I have not seen a bloom this large at this particular time of year," Caron said. "It's having an extraordinary impact on pelicans and many other species." "There are conceivably thousands of animals being affected," Caron said. The Wetland and Wildlife Care Center in Huntington Beach had received 73 sick or dead birds since Sunday, assistant director Lisa Birkle said. The toxin has been swifter and deadlier than usual, she said.