In 2010, Chelsea Wood was conducting a biological survey of the Line Islands, a chain of atolls and coral outcrops a thousand miles south of Hawaii. Some islands are heavily populated, home to a robust fishing trade, while others have never been permanently inhabited by humans. Seizing upon the opportunity afforded by such a stark contrast, Wood, then a budding parasitologist pursuing her Ph.D. in biology at Stanford University, decided to compare the worms living in the organs of fish from the uninhabited islands with those from the heavily fished areas.
What she found shocked her.
There’s a common perception of parasites as harmful, a harbinger of an ecosystem in distress, that’s shared by the public, and even many scientists. “We associate parasites with badness and destruc - tion and decay,” says Wood, now an associate professor in the School of Aquatic and Fishery Sciences at the University of Washington.
“We expect that when we mess up ecosystems, parasites should then come in to colonize, but it seems like actually the very opposite is true.” Indeed, contrary to Wood’s initial expectations, the fish from the pristine, unpopulated islands harbored more parasites than their counterparts. “Certainly more species of parasites, and for some kinds of parasites, more individuals as well,” says Wood.
With her discovery, Wood joined a small number of scientists on the leading edge of an invisible biodiversity crisis: the decline of parasites. It’s a struggle that’s gone largely unnoticed, concerning organisms that are widely reviled, but the studies that do exist suggest that parasites are in big trouble: In 2017, scientists compiled data about 457 species of parasites in a study in Science Advances. The researchers then produced models predicting that by 2070, up to 10 percent of those parasites will have gone extinct from climate fueled habitat loss alone. On top of that, habitat destruction that harms host organisms could spell the downfall of the many parasite species that depend on them.
