SAN FRANCISCO - Oceanographers are studying whether climate change is contributing to an unprecedented bloom of toxic algae that spans the Pacific Coast of the United States and Canada, raising health concerns and leading to multimillion-dollar income losses from closed fisheries.The bloom, which emerged in May, stretches thousands of miles from the Channel Islands off the coast of Southern California to Alaska's Aleutian Islands and has surprised researchers by its size and composition."It's just lurking there," Vera Trainer, research oceanographer with the Northwest Fisheries Science Center in Washington state, told Reuters on Thursday. "It's the longest lasting, highest toxicity and densest bloom that we've ever seen."The center is a branch of the National Oceanic and Atmospheric Administration (NOAA).The runaway bloom of pseudo-nitzschia algae is believed to have been spawned in part by unusually warm ocean water along the West Coast that scientists have dubbed "the blob."Scientists are also concerned about the looming El Nino effect, a recurring phenomenon that alters sea currents and temperatures, Trainer said.Researchers have yet to determine whether longer-term global climate change from rising levels of heat-trapping greenhouse gas emissions are playing a role, but the massive bloom may be a harbinger of things to come in any case, she said.