UW Study Shows Parasite Decline in Puget Sound

Image: University of Washington School of Aquatic and Fishery Sciences.

A University of Washington fisheries scientist says her research shows that fish parasites in Puget Sound have been in decline over the last century.

“We all have this sense that as climate change proceeds that what we get is increased parasite outbreaks; that we are messing with Earth and that Earth is messing (with us) right back,” Associate Professor Chelsea L. Wood of the UW School of Aquatic and Fishery Sciences said in early January. 

Until the study was conducted, Wood said, there was little information on wildlife parasites other than the impact of parasites on humans. What they were shocked to learn, she said, is that parasite life cycles are like Rube Goldberg machines; the more complex they are, the more likely they are to fail.

What Wood and her colleagues found was that parasites required only one or two host species to complete their life cycle and showed little change over time, while parasites that required three or more hosts declined by 10.9% every decade.

“We found that parasites that declined had more than three hosts they needed to complete their lifecycle,” she said.

Across taxa, the abundance of parasites with complex life cycles also decreased by 38% for every 1 degree Celsius increase in sea surface temperature, the study showed.

Effects of pollutant levels on parasite abundance varied across parasite taxa. Taxonomy is a branch of science dealing primarily with the description, identification, nomenclature and classification of organisms.

In all, the authors counted 17,702 parasites in 699 fish specimens collected from 1880 to 2019.

Wood, who teaches a course at UW on parasite ecology, noted that parasites do more than affect host populations.

“They are the check on a host whom we would not want to be an overabundance of the host species,” she said. “Parasites also are responsible for energy through food webs. They are often transmitted from prey to predator and can sometimes hurry that process along by making the prey more susceptible to predation.”

“In the process they are delivering dinner to the predator,” she continued. “They push energy up through the food web, subsidizing the diet of predators.”

“We invest a lot of dollars in predator conservation, and we are getting help with predator conservation with parasites,” she said.

Their findings suggest the need to measure parasite abundance in other ecosystems and assess the need for parasite conservation measures, the study’s authors said.