Dr. Joe Gaydos likes wildlife diseases.
Not in the sense that it makes him happy to see animals suffering, but that he’s fascinated by the biology of the diseases. Gaydos, with the SeaDoc Society, shared his enthusiasm about marine wildlife diseases as part of the Marine Science Lecture Series on Feb. 13.
“This is fun for me to talk about wildlife diseases,” Gaydos said. “It’s kind of like asking a barber to talk about doing haircuts – or something like that.”
In his presentation “Wildlife Diseases: How they affect wildlife, humans and marine ecosystems,” Gaydos said the discussion would be “more science-y” than usual.
“When people think about disease, they kind of think about … a really bad bug [that] comes, and it wipes everybody out except for the superhero,” he said. “You can have these ‘Andromeda Strain’ type viruses that can go haywire and cause a big problem, and these things can happen in people. They can happen in wildlife, too.”
Gaydos referenced Michael Crichton’s book “Andromeda Strain,” wherein a team of scientists try to stop an outbreak of disease, a handful of times during his talk. However, he said, his lecture was not about those large diseases but rather smaller diseases that are made worse by human involvement.
“We, as people, can exasperate problems that are already there,” Gaydos said. “By changing the availability and the amount of food that [is available] and the way things move from land to sea, we’re actually increasing the chances for animals to get these diseases.”
Gaydos’ first example was a canine distemper virus that spread from domesticated dogs to wild African lions in 1994.
“People say, ‘Disease happens all the time; it’s part of the ecosystem; it’s part of the ecology,’” Gaydos said. “And so people ask, ‘When do we need to be worried about it, or what kind of questions do we want to ask about it?’”
The first question scientists pose when faced with a disease outbreak is whether it is a single-animal infliction or if it could decimate an entire population, said Gaydos. Secondly, they determine whether it could spread to humans or domestic animals. “There’s a lot more money out there, a lot more concern out there for human health than there is for wildlife help. And there’s less money – but still a lot of money – out there for domestic animal health,” Gaydos said, adding that the primary concern is for cattle, sheep, pigs and goats. “So people are always asking, ‘Is this something we should be concerned about?’ Not just because they don’t care about wildlife but should we be concerned for human health or for domestic animal health?”
The third question is what is the outcome of the disease, and how can modifications be made to restrict the spread, said Gaydos. Scientists look at whether the disease can have catastrophic impacts on the ecosystem – like the sea star wasting epidemic that swept from Alaska to Mexico between 2013 and 2015. Gaydos explained that during the epidemic, sunflower sea stars were obliterated, which increased the urchin population. That, in turn, reduced the kelp population – an ecosystem engineer – ultimately decreasing the area’s biodiversity. Kelp isn’t the ocean’s only ecosystem engineer. Humans are as well.
“We as people can have unsuspecting impacts. … What happens on land really impacts the ocean,” Gaydos said. “There’s a lot of things – toxins, pathogens – that are moving from land into the sea. If you have natural barriers that can filter out things, it can filter out pathogens, but it can also filter out contaminants.”
Seagrass ecosystems have displayed the ability to filter bacteria out between the shore and coral reefs. In areas studied, there was a two-times reduction in coral disease in areas with seagrass. Marine wildlife disease has been observed increasing in areas where there is no bioswale between land and sea.
“You start to lose that buffering zone, so everything is running off the streets into the ocean water without having the benefit of having the upland vegetation, or in some cases the lowland or intertidal vegetation, like the seagrasses,” Gaydos said. The first example he gave of a disease-causing substantial damage to a species was that of sea otters in southern California. Following an outbreak of cyanobacteria (blue-green algae) on land, scientists observed the death of 21 sea otters. Their deaths were attributed to a microcystin resulting in liver failure – something that has never been observed occurring in the ocean, said Gaydos.
“Twenty-one otters. Why didn’t more otters die? Dietary preferences,” he said, explaining that the affected otters had eaten contaminated filter-feeders, like clams and mussels. “By having the specialization in diet, the animals are actually making themselves more susceptible to Toxoplasma (a toxin that is carried and transmitted by felines), just like they were making themselves more susceptible to microcystin toxin.”
Similar to the brucellosis infection that has plagued Yellowstone since the early 1900s, a disease called Brucella pinnipedialis affected local harbor seals. Because adult harbor seals typically stay within 15 miles of their preferred haul-out location, it made it easier to study what populations were affected the most, said Gaydos. Scientists discovered that more seals in South Puget Sound tested positive for the disease than those farther north. The waters in South Puget Sound are contaminated with higher levels of PCBs (Polychlorinated biphenyls), which affected the seals’ susceptibility to the disease.
“You have a pathogen that’s out there, and animals can get it. But if you have a contaminant that’s out there – that we’ve already put out there – animals are much more susceptible to actually getting the pathogen,” Gaydos said.
Harbor seals aren’t the only local species to have increased sensitivity to pathogens; the Southern resident killer whales are at risk as well.
“We have decreased salmon, we have increased underwater noise and then we also have contaminants, whereas an animal that didn’t have all those contaminants wouldn’t have a problem,” Gaydos said. The PCBs that lowered the seals’ immunity also affects the orcas. Typically the contaminants introduced by PCBs go into a whale’s blubber layer.
“So those contaminants sit in there and they’re inert – they’re not causing a problem. But if you’re hungry, or starving, and you start to draw down that fat supply, what’s going to happen? Those contaminants then become metabolically active, and they’re going to influence your immune system,” Gaydos said. “It’s a combination of multiple different things that we’re doing that are affecting animals.”
He said the orcas are being exposed to high toxin levels, vessel noise and a reduction in salmon availability, all of which are suppressing their immune systems and making them more susceptible to infections and death.
“You start to see that it’s not just that there’s this ‘Andromeda Strain’ disease that’s going on, but it’s all these other components that are keeping and helping – or actually causing – disease,” Gaydos said. “When you can understand all the interactive factors, then you can see the places where we as people can make a difference in getting rid of some of the factors that are the biggest ones.”