Disappearing parasites in Puget Sound: a bigger concern than you may think

An alarming number of parasites have been disappearing from Puget Sound for decades with little to no detection. While that may sound like good news, the reality is that parasites are crucial to ecosystems—and us.

For years, people have assumed that a warmer planet would lead to more parasites and disease. A groundbreaking study published in the Proceedings of the National Academy of Sciences is challenging that idea.

Dr. Chelsea Wood, a University of Washington parasite ecologist and lead author of the study, tells FOX 13 News that the decline of parasites in our region appears to mirror some of the most endangered species of our time. While Puget Sound has been warming, its parasites have been disappearing.

"There is an invisible biodiversity crisis happening," she said. "We have the first hints of it in Puget Sound, and what we saw is that parasite with the most complex life cycles are nose diving."

The study doesn't give a reason for the decline, but outlines three possibilities: the number of host species in Puget Sound, pollution or a shift in climate—the surface temperature of Puget Sound rose 1.8 degrees Fahrenheit between 1950 and 2019, making it the most likely culprit.

What is unclear, at this time, is whether this is a global problem or a Puget Sound problem. 

Dr. Wood notes that Puget Sound is an ecosystem that is highly studied, yet this information on parasite decline is just now coming to light. It's possible that similar parasite declines are happening across the globe, though more studies would be required to understand the true scope of the concern. Luckily, that work is possible – Dr. Wood said that museums across the country have similar collections that can be mined for data.

In this study, Dr. Wood and her team had to look at 140 years worth of fish samples that were held in the UW Fish Collection at the Burke Museum. The process, according to Dr. Wood, was simple but yet time-consuming. The team spent more than two years dissecting nearly 700 fish specimen They counted 17,000+ parasites – dozens of different types.

A jar of fluid-preserved fish specimens from the UW Fish Collection at the Burke Museum. These fish were collected in Hood Canal in 1991. Credit: Katherine Maslenikov/UW Burke Museum 

"We were really shocked that instead of increases of parasites over time, what we found were overwhelming declines," said Dr. Wood.

Parasites in Puget Sound declined at a rate of roughly 11% per decade according to this research. Parasite that relied on multiple host species suffered the fastest declines.

That may sound like music to some readers' ears. Parasites, by definition, are bad for their hosts. When the average person thinks of a parasite you're likely thinking of a visit to a veterinarian, or a doctor—but the number of parasites that harm humans is miniscule compared to the hundreds of thousands of parasites that exist, many which have no effect on us.

In fact, roughly half of all species on Earth are parasites. 

Dr. Wood is quick to point out those parasites play a critical role in the world around us – a parasite may be bad for a host, but that doesn't mean it's bad for everyone.

Parasites can have an invisible role in predator-prey relationships. They can control populations of animals whether through sickness, or weakening animals – essentially push predators to prey. Dr. Wood compared the plight of parasites to how wolves were run off and culled for decades. In the 1960s and 70s you'd be hard-pressed to find many advocates for wolves. While ranchers and rural residents have pushed back on the expansion of wolves in modern times, the sentiment has changed greatly in the general population.

Now, it's relatively accepted that wolves play an important role in food webs – Yellowstone National Park famously reintroduced wolves in 1995. That reintroduction aligns with meaningful changes in the area: from prey to plants, even insects and birds. The story of the changing look, and feel, of Yellowstone since the re-introduction has given people a new idea of what wolves mean to the greater ecosystem around them.

Dr. Wood is hopeful that parasites can get a similar PR boost in the future, and capitalize before it's too late – she's even among the authors of a paper that argued for a conservation plan for parasites.

"Out in nature, there are hundreds of thousands of parasite species that are doing really important things for ecosystems," said Dr. Wood.

The next step may be other scientists duplicating her team's work. Museums around the world have troves of animal samples, and Dr. Wood said this research can be extended beyond fish.  She estimates that billions of samples around the world are waiting to be tapped for valuable information that could give us a more complete picture of what is taking place with parasites around the globe, the work just hasn't been done yet.

"At every museum you've ever been to, there are hundreds, thousands, maybe millions of animals being held and preserved," said Dr. Wood. "They're essentially time capsules that can be exploited as parasitological data."

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Work is already underway in some areas to duplicate the findings in other ecosystems, though much more data is needed. Dr. Wood said that it's important we notice how important parasites are, before it's too late.