Rising Tide of Ocean Plagues

Four years ago, a disoriented sea lion created a stir by wandering past security onto the tarmac at San Francisco International Airport. Another addled sea lion took a wrong turn in the Pacific Ocean and found its way into California's Central Valley, surprising local citizens by traipsing through an artichoke field.

The two sea lions were treated for a powerful form of brain poisoning and survived. But hundreds of other sea lions have died, joining a short list of ocean animals that are succumbing to strange diseases.

In Florida, hundreds of manatees have died from an airborne toxin produced by "red tide." Infectious germs and toxins have killed bottle-nosed dolphins all over the eastern and southern coasts of the United States. And a parasite found in cat feces is taking the lives of sea otters off the coast of California.

Marine researchers are hesitant to say the world's oceans are sicker than usual. But they are raising the alarm that the ocean is changing -- possibly as a result of human interference -- and the evolving diseases are putting both sea animals and humans at risk.

"We tend to just get snapshots (of the big picture), but every single snapshot is pretty consistent in saying that we're pumping stuff into the ocean that's having all sorts of negative effects," said Andrew Dobson, a scientist at Princeton University.

Dobson and other researchers have been tracking the rise of ocean diseases for years. Last month, he and some fellow scientists issued warnings about the future of ocean health at the annual meeting of the American Association for the Advancement of Science.

The researchers pointed to several species facing problems. Sea lions off California, for instance, are suffering from poisoning by domoic acid, which is created when algae growth runs amok and "blooms" appear. Fish eat the algae and become poisonous to mammals who eat them, including humans and sea lions.

The poisoning cases in sea lions first began to appear in 1998, and California researchers have seen hundreds since then as beachgoers stumble upon animals undergoing seizures.

So far this year alone, 25 sick sea lions have been discovered. Many more are probably poisoned, said Frances Gulland, a veterinarian at the Marine Mammal Center in Sausalito, California.

Humans suffer from memory loss when they eat seafood contaminated with domoic acid -- algae-related toxins cause a variety of neurological problems -- and researchers think the sick sea lions are suffering from a similar condition. That explains why the animals do strange things like wander out of the water and become overly friendly or aggressive when they encounter humans, Gulland said.

Scientists treat the sea lions with the human drug lorazepam (Ativan), a tranquilizer that calms their seizures. But even with treatment, about half the sea lions die, Gulland said.

Sea lions are also dying of a sexually transmitted cancer that reminds researchers of Kaposi's sarcoma, a disease that causes potentially fatal lesions in AIDS patients.

In Florida, scientists have watched manatees die from poisoning by so-called brevotoxins, which are produced by algal blooms known as red tides. The manatees apparently breathe the toxins and become sick.

California sea otters are succumbing to toxoplasmosis, a disease best known for infecting unborn children if their mothers come in contact with cat feces.

Scientists only have one explanation for this affliction: Parasites from cat feces are making their way into the ocean and infecting the sea otters. "What our pets do can affect not only us but also the mammals in the sea," said Patricia Conrad, a scientist at the University of California at Davis.

Scientists say humans are likely responsible for the changes in the ocean that are boosting these diseases, but they aren't sure exactly what's going on.

In the case of algal blooms, possible causes include fertilizer runoff, climate change and over fishing. Pollutants like DDT could be responsible for the cancer rate in sea lions, while flame retardants and stain-resistant compounds could explain die-offs of marine mammals like dolphins.

And the cats and the sea otters? It's not entirely clear what role humans play on that front: Are cat feces getting into the ocean through kitty litter flushed down the toilet? Or through runoff from neighborhoods where feral cats live?

For now, Conrad advises cat owners to keep pets indoors and dispose of kitty litter in plastic bags.

While the causes of the emerging diseases in the ocean are a mystery, one thing is certain: They have the potential to reach out and strike humans on land.

Domoic acid in algal blooms can contaminate seafood and sicken humans who eat it. And researchers in Florida have linked red tides with higher rates of respiratory-related emergency room visits, possibly because the algal blooms create airborne irritants.

The good news? Scientists don't seem worried that the equivalent of bird flu -- say, a "fish flu" -- is lurking in the ocean, waiting to strike at humankind. The ocean, it seems, has plenty of toxins but isn't the best incubator of infectious diseases that kill humans.

Still, the sea is changing. "There are definitely changes in the ocean's ecosystem that indicate it's not this great blue water that’s going to stay the same forever," Gulland said.