For several years now, dead otters have been puzzling marine biologists. The mystery began in 2007 when nearly a dozen otters mysteriously died in Monterey Bay. Their carcasses were taken to the California Department of Fish and Game laboratory in Santa Cruz for analysis.
It turns out the otters are being poisoned by a microbe, a type of cyanobacteria that appears to be on an upsurge in warmer, polluted waters around the world. Cyanobacteria are commonly called blue-green algae, blue-green bacteria, and Cyanophyta. They are a type of algae that get their energy from photosynthesis, and their name from their vivid color – cyan.
This particular cyanobacteria is called Microcystis, and it’s not new or rare. It’s an ancient ancestor of modern-day bacteria and algae, and it dominated the planet more than 2.5 billion years ago. Scientists have found that strains of it are reappearing in stagnant water polluted with nitrogen from agriculture, and waste from human activities. It’s been found in water in every country in the world.
Microcystis is absorbed into the tissues of shellfish in contaminated water. There it remains, becoming more than 100 times more concentrated that it is in the surrounding water. Otters eat the shellfish and get sick and die.
The otter population off the California coast has dropped in recent years, which means that adult otters are dying faster than baby otters are being born.
California’s otters were hunted, almost to extinction, by fur traders in the early part of the 19th century. Otter fur had long been prized by Native Americans and other cultures for it’s incredible warmth and softness. Otter fur soon became in demand as a luxury item in many parts of the world and otters were hunted until they were almost entirely wiped out.
The rebound of the otter population on the North Coast has been an ecological success. However, they are still an endangered species and are always subject to threats such as sharks, watercraft, parasites, and food shortages.
Right now, there are about 2,700 otters living on the California coast.
The discovery that the algae is killing otters was made by Melissa Miller, a state wildlife veterinarian who has been tracking the mysterious deaths like a detective. (Visit her website here.) You can read more about how she made this important discovery in this fascinating article in the Los Angles Times.