A recent study by UC Davis researchers showed that declining populations of sea otters could be attributed to pathogens in their diet.
Such pathogens are also influencing their behavior on the sea floor, slowing their biologically inclined recovery times – the time it takes an otter to come up to shore. Conditions such as brain disease are becoming more prevalent and a strong link has been found to their nutrition intake.
Sea otters have been a threatened species for a number of years and their populations have been hitting record lows. Christine Johnson, the lead author of the study and a veterinary epidemiologist at the UC Davis Wildlife Health Center, conducted the research in hopes of gaining insight into their deterioration and how it could be fixed.
“Sea otters are important because they are a keystone species for the near shore ecosystems,” Johnson said, explaining that sea otters play an important role in the biological concept of biodiversity.
“Our study was prompted by two observations. First, we have found over the past decade that sea otters have been suffering high levels of mortality from infectious disease, and we suspected that many of these diseases were transferred to the otters via their prey. Secondly, we had discovered that sea otters exhibited high levels of individual variation in diet, and that this tendency seemed to be linked to food abundances,” said Tim Tinker, a co-researcher in the study and assistant research biologist at UC Santa Cruz.
This led the researchers to examine two key factors that limit sea otter population growth: disease and resource limitation.
One disease sea otters are inflicted with is brain infections caused by ingesting toxins. There are two bacteria that increase the risks of brain infection – Toxoplasma gondii and Sarcocystis neurona.
“Both pathogens cause brain disease in otters and cause mortality – we were curious to see why some sea otters were getting exposed to these pathogens and others weren’t,” Johnson said.
These two bacteria seem to be prevalent in the sea otter diet. The study showed that sea otters are having difficulty obtaining adequate nutrition and therefore settled on eating things that lack any nutritional content.
Sea otter diet is the best when they can feed on abalone. This preferred diet has, however, proven to be more difficult to obtain and thus the otters have been resorting to feeding on marine snails, clams and small crabs. This novel diet contains T. gondii strains and S. neurona strains depending on which region the sea otters are living in.
Depending on the habitat that the sea otters lived in, the bacteria was more prevalent. Sea otters living near San Francisco’s Fisherman’s Wharf and Monterey’s Cannery Row were more susceptible to S. neurona bacterial strains. Those living along the Central California coast near San Simeon and Cambria were prone to T. gondii strains.
The study’s implications consist of trying to regenerate abalone and trying to train sea otters to stray from their dangerous diet. Researchers aim to discover how the diet can be readjusted and save the food web.
SADAF MOGHIMI can be reached at features@theaggie.org.
