In the last five years, 24 sea otters have stranded and died in the Monterey Bay area. Veterinarians noticed a strange yellow coloration to the animals, so they performed necropsies and determined that the cause of death was something pretty unexpected- microcystin.
Microcystin is a cyanotoxin produced by algae, and because it’s generally found in freshwater, deaths in ocean mammals are particularly troubling. Investigation led researchers to a nearby freshwater lake, where they used ‘artificial clams’- small bags of polystyrene beads- to give them some answers. The bags can be left in the water for periods of time, and much like real clams, they passively absorb toxins. Later, they can be analyzed to determine toxin levels over a period of time.
Researchers confirmed that the lake was the source of the problem. They found that a combination of natural phosphorous in the underlying rock combined with chemical runoff from local agriculture created the perfect environment for the algae that produces microcystins. When the lake water fed into the ocean, invertebrates such as clams and mussels in the ocean collected the toxin and concentrated it. When sea otters fed on the toxic clams, they were slowly poisoned.
They’ve found the source, but now it’s a question of how to address it. Researchers are working on potential treatments for microcystin poisoning (with the help of rats!), and hopefully, this will lead to treatments that can help marine animals as well as humans.