"Human activities are knocking things out of balance," says Andrew Dobson of Princeton University. "For some pathogens, we're seeing nasty synergistic effects with contaminants, such as PCBs. Paradoxically, diseases also play an important role in healthy ecosystem functioning. These changes tend to slip under the radar screen until they show up in ecological cascades that lead to wildlife and human health problems."
Lethal Domoic Acid Poses New Threats to Sea Lions & Humans
Scientists studying sea lions in California are seeing an increase in the number of animals affected by domoic acid, a toxic compound produced by specific types of algal blooms. In high doses, domoic acid is fatal. At lower doses, it can trigger miscarriages and cause gradual, irreversible decay of brain tissue.
Many scientists agree that increases in algal blooms in California and around the world are caused by a combination of factors, including agricultural run-off, oceanographic properties, and global warming. Many of these blooms produce chemicals that are dangerous to humans when concentrated in the food chain. In the case of domoic acid, both shellfish and fish can concentrate the toxin.
Scientists first saw domoic acid poisoning in 1998, when over 70 sea lions died in one weekend. "We thought at the time that it was linked to the fact that it was an El Nino year, but we've seen it every year since then," says Frances Gulland of The Marine Mammal Center in Sausalito, California. "It's a big mystery."