How Invasive Elodea Affects Juvenile Salmon in Alaska

Installing experimental enclosures at McKinley Lake, Alaska, to compare habitats dominated by the invasive Elodea with habitats that are not. U.S. Geological Survey.

Invasive species are reaching high-latitude ecosystems faster, because of a warming climate, more travel and changing land use. The aquatic plant Elodea could spread widely through the Arctic and Subarctic, and is already established in 19 waterbodies in Alaska.

Elodea is known to change freshwater habitats in several ways, but little is known about its effect on fish, above all on juvenile Pacific salmon. It grows in dense stands in shallow water, where young fish hide from predators and feed.

The experiment

Led by the U.S. Geological Survey with partners from the U.S. Forest Service and the National Park Service, the study tested how Elodea affects the growth of juvenile coho salmon (Oncorhynchus kisutch) in an infested lake near Cordova, Alaska.

What it found

• Growth and diet. Young coho raised among Elodea grew less over the summer, and ate differently (at a lower trophic position), than those among native aquatic plants.
• Water. Infested sites showed no significant change in water conditions or primary productivity compared with native-plant sites.
• Prey. Infested sites had fewer zooplankton. The taller the Elodea and the richer the vegetation, the more macroinvertebrates there were.

Together, the results suggest that Elodea changes the flow of energy to young salmon by restructuring their space and their prey. If it becomes widespread, it may lower the quality of salmon rearing habitat and, by slowing the growth of young fish, could affect the numbers of salmon returning.

More

• USGS: the effect of Elodea on fish performance through food webs
• USGS data: limnological data from the experiment

Sources

• National Park Service, "How does Elodea impact juvenile salmon?" https://www.nps.gov/articles/000/elodea-impacts-on-salmon.htm
• M. P. Carey, G. H. Reeves, S. A. Sethi, T. L. Tanner, D. B. Young, K. K. Bartz and C. E. Zimmerman, "Elodea mediates juvenile salmon growth by altering physical structure in freshwater habitats," Biological Invasions (2023). https://link.springer.com/article/10.1007/s10530-022-02992-3
• Words on this page from people and organisations outside the federal government are paraphrased; rewritten in hubnx's own words.