Earth Protect Blog

A toxin produced by a type of cyanobacteria, also known as blue-green algae, has been devastating a colony of sea otters off the coast of California. In a paper published in the journal, PLoS ONE, by the California Department of Fish and Game (DFG) and the University of California (UC), Santa Cruz, researchers link the deaths of over 21 California sea otters to toxic chemicals from algae flowing into the ocean.

Blue-green algae itself can be detrimental to the natural ecosystem

because it can block light from reaching the depths of the water and starve the water of dissolved oxygen. Once the oxygen goes, no marine life can survive and you get "dead zones." Now, according to the researchers, one particular type of algae is also releasing a deadly toxin known as Microcystis.

Warm, nutrient-rich fresh water systems are ideal for large blooms of Microcystis. The toxic algae can resemble slimy green goo as it as it forms a thick green mat over the surface of the water. Eventually the fresh water flows into the ocean, carrying the algae with it. However, the toxin does not break down right away as it reaches the salt water. It can last well over three weeks without any serious degradation.

The Microcystis can cause acute liver failure, damage body tissue, and be fatal, as was witnessed with the sea otters. Melissa Miller, lead author of the study and senior wildlife veterinarian at the DFG, began recovering the dead otters along the shore of Monterey Bay in 2007. This sparked a wider search for the sources of the toxin. The search lead the scientists to Pinto Lake in Watsonville, a lake with a history of Microcystis blooms. Pinto Lake drains into Corralitos Creek, then into the Pajaro River, one of three main rivers to empty into Monterey Bay.

In the ocean, the Microcystis can be eaten or absorbed by creatures such as oysters, mussels, clams, and crabs, which are then consumed by sea otters. Deaths from this toxic bacteria have attributed to the overall decline of the California sea otter population. According to co-author Tim Tinker, "These findings also show the value in closely monitoring sentinel species like sea otters as a way to detect and understand threats to coastal oceans."