May 2022, ScientificAmerican.com 67like, ‘You want to do what to our specimens?’ ” Masle-
nikov recalls. Many conversations later, she came
around. Wood’s project, Maslenikov realized, “is a
whole new avenue of research”—a chance to fulfill the
museum’s mission of aiding cutting-edge scientific
studies. As Maslenikov put it, “This is not dead storage.
A collection is meant to be used.”
HISTORICAL ECOLOGY
katie leslie is sorting through ribbons of intestines
belonging to a rockfish that’s been dead for 41 years.
So far Leslie, a research technologist in Wood’s lab,
has found only the remnants of the animal’s last meal.
Rockfish are notoriously wormy, but this specimen is
proving to be exceptionally parasite-free, until—
“Oh, wait, yes!” Leslie calls out. “Here’s an
acanthocephalan!”
Under the microscope is the first parasite of the
day, a thorny-headed worm. Leslie goes on to tally
seven more parasites, including flatworms and nem-
atodes. She then carefully places the fish, along with
its neatly labeled vial of organs, back into its jar, and
reaches for the next one.
To begin investigating the question of winners and
losers, Wood chose eight common Puget Sound fish spe-
cies from the collection. Maslenikov helped her iden-
tify up to 15 specimens per species per decade, starting
as far back as the 1880s. In the lab, each fish undergoes
a full physical, inside and out, first for sea lice attached
to the animal’s skin and then for parasitic worms in its
organs and gills. Technologically speaking, the method,
Wood admits, is “like banging two rocks together.”
Finding the parasites is just the first step. Worms
can be incredibly difficult to tell apart, with visual dif-
ferences coming down to the number of teensy spines
or hooks on a microscopic appendage. Species identifi-
cation is therefore an exercise in patience and meticu-
lous taxonomic expertise. “Our work supports the value
of morphological taxonomy,” says Rachel Welicky, a for-
mer postdoctoral researcher in Wood’s lab, now work-
ing as an assistant professor at Neumann University in
Pennsylvania. “It’s really becoming a lost art form.”
In July 2021 the Wood lab reported findings in Fron-
tiers in Ecology and the Environment from its first
analysis, on English sole collected from 1930 to 2019.
In more than 100 specimens, the researchers identi-
fied nearly 2,500 parasites representing at least 23 taxa,
of which 12 were prevalent enough to analyze their
population trends over time. Of those 12, nine did not
change in abundance across the decades; two, a trem-
atode and a thorny-headed worm, decreased; and
another, a trematode, increased. In another study that
spun out from the same analysis of English sole, pub-
lished in 2018 in the Journal of Applied Ecology, the
team also found that a nematode called Clavinema
mariae —a bloodworm that creates unsightly lesions
on its host’s skin—underwent an eightfold increase
over the 86-year period.
According to Lafferty, who was not involved in the
research, those results “demonstrate a new value for the
millions of pickled fish in jars on museum shelves
across the world.” The findings themselves are notable,
he continues, because they add an important data point
about how parasites respond differently to environmen-
tal change. English sole parasites have been surprisingly
stable over time, but for those whose populations did
shift, not all went up. “Just like for free-living species,
some parasite species do well under stress, and others
don’t,” Lafferty says. Wood and her colleagues are pre-
paring another study for publication with even greater
power to test the “winners and losers” hypothesis.
As the team meticulously works through museum
specimens, the scientists are also turning to other
resources. Although there are few long-term data sets
on any parasite species, there are one-off studies that
document the abundance of parasitism at a particular
place and time. In a 2020 Global Change Biology paper,
Wood and her group synthesized these results for two
types of common parasites found in raw fish often used
in sushi and ceviche. One of the worms, they found, is
just as prevalent today as it was in the past, but the
other worm underwent an incredible 283-fold increase
since the 1970s.
Wormy sushi can lead to a bad case of vomiting and
diarrhea when consumed by people, but Wood is con-
cerned about marine mammals—the worm’s intended
targets. Typically a single worm does not extract much
energy from its host. But if the number of worms is sky-
rocketing, they could pose a problem for marine mam-
mals, especially for populations that are already
stressed. The Puget Sound’s endangered pod of resi-
dent killer whales, for example, suffers from pollution,
noisy ships and a lack of Chinook salmon to eat. In 2018
an emaciated killer whale calf turned up in the sound.
Authorities launched an unsuccessful effort to save her,
and before the calf died, scientists found that her scat
was loaded with parasite eggs of the same sushi worm
family identified in Wood’s study.
This does not prove that parasites played a role in
the calf ’s death. But it does hint at the possibility that
parasites might be making life harder for an already
beleaguered population, Wood says. To learn more,
Natalie Mastick, a doctoral student in Wood’s lab, is
using several approaches to understand whether
whales are facing a greater threat of intestinal parasit-
ism today than they did in the past—such as collecting
whale poop found by sniffer dogs on boats and analyz-
ing it for hormones, diet and parasite load. “If para-
sites turn out to be this huge stressor we didn’t know
about, at least that’s a treatable ailment,” Mastick says.
Wildlife managers can tuck anthelmintic drugs inside
the salmon they feed to worm-stricken marine mam-
mals (“like hiding your dog’s pill in a blob of peanut
butter,” Wood says) or use darts to administer the phar-
maceuticals from a distance.
In addition to the possible impacts on health for
humans and wildlife, spikes in parasite populations
can harm certain industries. The Puget Sound, for