Sea Otters and Marine Pollution
Coastal Habitat and Shellfish Diet Lead to High Contaminant Exposure
Sea otters immune compromised by marine contaminants. Heart disease, toxoplasmosis and other infections seen. Some shark attack deaths may be result of increased disease.
In California southern sea otters (Enhydra lutris neris), originally hunted for their lush pelts, are still endangered, despite efforts to protect them. Evidence suggests that marine pollutants are having both direct and indirect effects on the health of these charismatic marine mammals.
Toxoplasmosis and Sarcocystis Encephalitis in Sea Otters
Exposure to Toxoplasma gondii, the parasite found in cat feces, is causing encephalitis (brain infections) in sea otters. So is Sarcocystis neurona, a common parasite of the opossum (Didelphis virginiana). Both of these parasites are believed to be entering the coastal ocean habitat of the otter via coastal runoff.
What is most worrying about the parasitic encephalitis is that these parasites rarely cause the level of illness that is being seen in sea otters. In humans, it is generally only those who are immuno-compromised that develop such severe disease.
Shark Attacks on Sea Otters
In the wild, each species has predators, so the loss of sea otters to shark attack would seem to be a normal part of the life cycle of the ocean. But a closer look at the animals killed by sharks showed that many had parasitic encephalitis as well. The otters with encephalitis had problems with motor coordination, likely making them easier prey.
Heart Disease in Sea Otters
Two separate causes of heart problems have been found in sea otters. The first is inflammation of the heart caused by sarcosystis and the second comes from domoic acid exposure which sometimes results in damage to the heart muscle.
The Role of Marine Pollutants in Sea Otter Mortality
In the late 1990s research showed that sea otters had been exposed to high levels of Tributyltin (TBT), a product in anti-fouling paint used to protect boat hulls. This led to liver damage in exposed otters. Some otters were also found to have high levels of PCBs.
Most of the otters dying of infectious disease were found to have higher levels of marine pollutants than other otters. These types of marine pollutants are known to damage the immune system, making the exposed animals more prone to disease.
Nitrogenous waste pollution is implicated in the increase in Harmful Algal Blooms, including the ones that produce domoic acid. And, as discussed above, fecal contaminants leached into coastal waterways are having a very direct impact on sea otter health.
Because sea otters live and feed in the nearshore coastal area they are important sentinels of ocean health. Their shellfish diet causes them to accumulate any contaminants that have settled on the sea floor. Their nearly totally aquatic lifestyle means they are constantly exposed to whatever is polluting the sea. Monitoring sea otter health gives insight into the health of the ocean, which directly affects human health as well.
Sources:
Thomas, N. Sea Otter Mortality, USGS
