Red Tides, Domoic Acid, Coral Diseases - Human Pressure Crushing Sea Life

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A leading group of epidemiologists, veterinarians and ecologists report that humans are affecting the oceans in ways that are changing the dynamics of disease. Previously harmless pathogens are becoming killers when combined with contaminants; "good" parasites that invisibly control the balance of species in an ecosystem are disappearing; and changes in sea surface temperature can trigger cholera outbreaks thousands of miles away. "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.

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In the struggle to understand and prevent coral diseases, scientists are finding that sugars released in sewage and agricultural run-off play an unexpected role in killing corals. In the 1970's there were only a few diseases documented on coral reefs. Today there are over thirty, and the numbers are increasing exponentially. "The scary thing is that even in the Great Barrier Reef, one of the most protected reefs in the world, researchers are seeing more diseases every time they look," says David Kline of the Smithsonian Tropical Research Institute.

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Sugars that promote this dangerous overgrowth reach the ocean directly from human waste and agricultural run-off, but are also produced by fleshy algae. This link to algae reveals an escalating feedback loop. Nitrogen and phosphorus pollution in run-off enhances the growth of algae that produce simple sugars as they photosynthesize. The sugars, in turn, promote the growth of bacteria, which kills or weakens the coral. This leaves more room for the algae to take over, smothering corals and increasing sugar production, starting the cycle over again and rapidly changing reefs to fields of algae. In healthy systems, some of this algal growth would be kept in check by fish and other algae-eaters, but overfishing has wiped out many of these populations. "Corals are tough, they've been around for millions of years. But multiple threats such as pollution, overfishing, and global warming may prove to be too much for them," Kline says. "I've seen Staghorn reefs go from brilliant areas that form a nursery for fish, to completely wiped out, in a matter of months."

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http://www.medicalnewstoday.com/medicalnews.php?newsid=38081