CSI Great Lakes: genetic material helps researchers find invaders

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Capital News Service

LANSING — Environmental DNA is a genetic material Great Lakes researchers have used to detect the presence of species for about the last 10 years. 

Now it’s playing an increasingly important — but sometimes controversial — role in monitoring invasive species.

Known as eDNA, it was initially used to detect and describe microbial communities in marine sediments in the mid-1980s and phytoplankton communities in the water column since the early-1990s.

It can be found loose in the water or in sediments, said Carol Stepien, the Ocean Environment Research Division leader for the National Oceanic and Atmospheric Administration. 

“It’s outside the organisms. So maybe it’s cellular material or waste products and things that were shed by the organisms that are given off,” said Stepien, who is based in Seattle, but has worked for about 25 years in the Great Lakes.

NOAA scientists test eDNA in Great Lakes areas that they are interested in.

“They may test ballast water from ships coming into the Great Lakes,” Stepien said. “And they also may test harbor areas or places where organisms tend to be introduced.”

Lucas Nathan works with fish eDNA as the aquatic invasive species coordinator for the Michigan Department Natural Resources Fisheries Division.

“This would be any sort of genetic material that a fish is going to release into the water,” Nathan said.. “This can be scales, slime, it can become a tissue, it can be excrement that they release, and that material all contains genetic genetically identifying material.”

It’s not always easy to apply this emerging technology when he tests eDNA in water.  One challenge is that finding eDNA does not mean the detected species is alive and present in that lake. 

“This could be the result of a dead individual that’s present that’s releasing DNA into the water, even though it’s not alive,” Nathan said. “Or it could be the result of runoff.”

He described one such possibility:

“Maybe the fish is actually present in a water body upstream. And through connections through rivers and streams, you could have DNA flowing downstream into that system, which would result in detection, even though the live organism isn’t there.”

Another potential cause of inaccurate results is contamination-related. 

Technicians could get DNA on gear or boats and other equipment. That DNA could be transported into a new body of water that doesn’t have those species. 

The presence of a species can be verified by technicians using traditional gear such as nets or electrofishing that uses direct current electricity to catch fish. The additional surveys can confirm whether the eDNA found in a particular body of water represents a live organism before taking additional steps to eradicate it.

A related challenge is a need for a better connection between eDNA results and management actions, according to a recent research paper in the journal Trends in Ecology & Evolution. 

The study from the U.S. Geological Survey said invasive species managers will face the dilemma of deciding whether to act based on positive eDNA tests. 

Acting on a false positive could result in needless costs and inconvenience, the study said.

For example, DNA-based monitoring of invasive Asian carp in the Great Lakes region has generated intense criticism by some industries that use the Chicago shipping canal. That led to court cases seeking to close locks and dams that are critical to commerce.

Invasive species that eDNA testing aims to tackle in the Great Lakes have a great impact on ecology.

NOAA’s Stepien said the effects of invaders like zebra and quagga mussels affect the food chain.

“They covered the bottom with their shells and spread. They have dramatically changed the benthic, the bottom ecology in the Great Lakes,” she said. 

Another invasive species, Asian carp, filter very low on the food chain, taking food from other species.

“They filter the water and get little tiny organisms. They deplete the food for fish that are desirable for people to eat and catch commercially and recreationally. So it really affects them,” Stepien said.

Yue Jiang writes for Great Lakes Echo.

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