Forget 'needle in a haystack'; try finding an invasive species in a lake

December 04, 2018

MADISON, Wis. -- When the tiny and invasive spiny water flea began appearing in University of Wisconsin-Madison researchers' nets in 2009, scientists began to wonder how Lake Mendota, one of the most-studied lakes in the world, went from flea-free to infested seemingly overnight. Subsequent studies found the invader had persisted for years at low population densities that went undetected even as the lake was routinely sampled by trained technicians.

Now a new report published in the journal Ecosphere says Lake Mendota's story may be the rule, rather than an exception.

"Our original idea was (to ask): 'How is this possible? In what scenario would we miss spiny water flea for 10 years, even after so much effort?'" says Jake Walsh, lead author of the study and a postdoctoral researcher at the UW-Madison Center for Limnology.

The answer is that completely missing a species "is not only possible, it's likely," says Walsh, noting that the study can help inform invasive species ecology and is a "way of using math and computer modeling to fill in the blanks of what we see."

With Center for Limnology director Jake Vander Zanden and Eric Pedersen, a colleague from Fisheries and Oceans Canada, Walsh developed a theory of the probability of detecting a species as its population densities change.

Their modeling shows that when species are in low abundance in a given habitat, the ability for scientists to detect them drops off precipitously.

This may explain why spiny water fleas passed undetected in Lake Mendota for a decade. Early on, researchers would have needed to dip their nets into the lake "hundreds or even thousands" of times, Walsh says. Once the invaders became more abundant, detection became much easier: "You can go out sampling three times and likely detect spiny water fleas."

Part of the problem is size. Even if there was one spiny water flea for every cubic meter of water in Lake Mendota, catching one in a net would be like finding a sesame seed in roughly 250 gallons of water.

One of the solutions, the study shows, may be for scientists to increase the size of the funnel-shaped plankton nets they drag through the water when looking for the small creature. Standard nets are roughly a foot in diameter, but by upgrading to a one-meter-wide net (about three feet in diameter), "your detection increases by quite a bit," Walsh says.

Being more deliberate about sampling for spiny water fleas and other invasives at the right places and times may also improve scientists' chance for detection, Walsh says. Spiny water fleas are a type of zooplankton (small, free-floating crustaceans) that travel in groups called swarms and are pushed around by wind and currents. A swarm may move at any time out of any given sampling site. And their abundances vary throughout the year. For instance, spiny water fleas are present in the greatest numbers in Lake Mendota in the fall.

"If you were to double your effort at sampling for spinies in the fall," Walsh says, "you get the same advantage as if you were to double your effort across the entire year."

The study offers some "basic rules of thumb" for designing species surveillance programs of any kind -- from likely invasives to rare or endangered natives, Walsh says.

"It has to do with targeting our efforts better and finding times of the year where things are more abundant or areas where they're more abundant because that dramatically increases your detection rate," he says. "If you take a little extra time to get to know the species you're looking for, it can really pay off."
-end-
--Adam Hinterthuer, hinterthuer@wisc.edu, 608-630-5737

DOWNLOAD PHOTOS: https://uwmadison.box.com/v/spiny

University of Wisconsin-Madison

Related Water Articles from Brightsurf:

Transport of water to mars' upper atmosphere dominates planet's water loss to space
Instead of its scarce atmospheric water being confined in Mars' lower atmosphere, a new study finds evidence that water on Mars is directly transported to the upper atmosphere, where it is converted to atomic hydrogen that escapes to space.

Water striders learn from experience how to jump up safely from water surface
Water striders jump upwards from the water surface without breaking it.

'Pregnancy test for water' delivers fast, easy results on water quality
A new platform technology can assess water safety and quality with just a single drop and a few minutes.

Something in the water
Between 2015 and 2016, Brazil suffered from an epidemic outbreak of the Zika virus, whose infections occurred throughout the country states.

Researchers create new tools to monitor water quality, measure water insecurity
A wife-husband team will present both high-tech and low-tech solutions for improving water security at this year's American Association for the Advancement of Science (AAAS) annual meeting in Seattle on Sunday, Feb.

The shape of water: What water molecules look like on the surface of materials
Water is a familiar substance that is present virtually everywhere.

Water, water everywhere -- and it's weirder than you think
Researchers at The University of Tokyo show that liquid water has 2 distinct molecular arrangements: tetrahedral and non-tetrahedral.

What's in your water?
Mixing drinking water with chlorine, the United States' most common method of disinfecting drinking water, creates previously unidentified toxic byproducts, says Carsten Prasse from Johns Hopkins University and his collaborators from the University of California, Berkeley and Switzerland.

How we transport water in our bodies inspires new water filtration method
A multidisciplinary group of engineers and scientists has discovered a new method for water filtration that could have implications for a variety of technologies, such as desalination plants, breathable and protective fabrics, and carbon capture in gas separations.

Source water key to bacterial water safety in remote Northern Australia
In the wet-dry topics of Australia, drinking water in remote communities is often sourced from groundwater bores.

Read More: Water News and Water Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.