BELLEVUE, Wash.
(AP) - When salmon, salamanders or other aquatic animals poop or shed skin
cells, they leave behind traces of their DNA in the water, like clues left
behind at a crime scene.
It’s this evidence
that Kit Paulsen is seeking as she wades into an urban creek east of Seattle
and fills a 4-liter jug with water. In a few minutes, she has a sample that
will reveal whether a tiny destructive New Zealand mudsnail is present in
the salmon-bearing stream.
At one-eighth of an
inch, the snails are incredibly hard to find. That’s why scientists are
turning to environmental DNA, or eDNA, an emerging surveillance tool that
detects the presence of an organism by analyzing cellular material such as
urine, hair, feathers or skin cells that are left behind in the environment.
Whether it’s Asian
carp in Chicago-area waters, salamanders in Kentucky or great crested newts
in the United Kingdom, biologists are using the tool to help look for
reclusive or rare imperiled species, monitor unwanted creatures or gauge the
overall biodiversity of a lake or stream.
“We’re starting to
realize its potential,” said Caren Goldberg, an assistant professor at
Washington State University who is managing editor of a special issue on
environmental DNA in the journal Biological Conservation. Her lab in
Pullman, Washington, will analyze samples that Paulsen and her team
collects.
Paulsen, the city
of Bellevue’s watershed planning supervisor, consulted with Goldberg after
hearing about the method, and this spring, the city plans to test samples
from 22 urban streams and eight beaches.
Bellevue has
invested so much time and millions in salmon habitat and restoration that it
can’t afford to let the invasive snails take hold, Paulsen said. The snails
multiply rapidly, compete with native fish for food and can’t be eliminated
once they infest a stream.
Using eDNA is
cheaper and quicker than visual surveys, Paulsen said, though it’s not meant
to replace it. At about $50 a test, including equipment and lab costs, the
total cost of $12,500 is less than what it would take if employees walked
those streams turning over rocks, she said.
Environmental DNA
has been used for about a decade to detect microorganisms in soils and
sediments. More recently, it’s been used to monitor endangered Chinook
salmon in Washington state, secretive amphibians in Idaho, and protected
eastern hellbenders in Ohio and Kentucky.
In one study,
scientists found that eDNA was more effective than traditional methods, such
as visual searches for eggs, in detecting imperiled great crested newts in
the United Kingdom. They concluded it could be used effectively for a
national citizen-monitoring program.
Environmental DNA,
however, won’t tell scientists exactly how many animals are there, only that
they’re present, or whether the animal is alive or dead. Material also
typically breaks down in the environment in a week or two. And like any
test, there’s a possibility for false positives if certain collection or
other protocols aren’t followed.
Still, many
supporters say it holds huge potential for conservation biology.
In northeastern
Washington, the Confederated Tribes of the Colville Reservation had been
looking for affordable ways to monitor efforts to reintroduce spring Chinook
in the Upper Columbia River.
Spring is a
difficult time to detect the fish because of high runoff, and it’s also hard
to get out into backcountry areas, said Matthew Laramie, a U.S. Geological
Survey ecologist in Boise, Idaho.
He and others
tested whether eDNA could be a good tool. They confirmed Chinook salmon in
sites where they were known to be, and also picked up evidence of the fish
in areas where they had not been seen before but could actually swim to.
Separate tests did not pick up signs of the fish in areas where they could
not swim to.
Laramie said it
likely won’t replace fish counts, “but it’s a way to weed through a large
system and prioritize resources.”