The Lake Where You Live

All things by immortal power, near of far, to each other linked are, that thou canst not stir a flower without troubling of a star. — Francis Thompson

I’ve written previously about one effect of rusty crayfish here on Birch Lake. When their population exploded, they mowed down the aquatic plants. Now that their population has crashed, the plants are coming back.

Except now the dominant species is not the large-leaf pondweed (cabbage weed) prized by anglers, but coontail, less productive as habitat for fish. It’s a lesson in how, when an ecosystem is disrupted, the impacts reverberate, and recovery, if it happens all, takes time. 

Maybe the quote above overstates things, but the basic idea holds. In a lake or any natural system, there are connections we may not understand. 

When the rusty crayfish wiped out the weed beds in Birch Lake, the fishery changed dramatically. Perch and panfish, robbed of cover, declined. Smallmouth bass, which prefer more barren rocky habitat, flourished while feeding on the crayfish. Now that the crayfish are mostly gone, the smallmouths are fewer and not as robust in size.

As for the plant life, a couple of scientific papers, one from the University of Illinois and one from Notre Dame, shed some light on the changes and the reasons for them, in Birch and other lakes that have seen similar cabbage-to-coontail transformations.

The Illinois paper notes that rusty crayfish in lakes have been studied since 1975 and that their populations have declined in about half the lakes surveyed. For the current paper, published in 2023, the researchers studied the recovery of aquatic plants and snails in 10 lakes in Vilas County after long years of rusty crayfish invasion. 

They compared lakes where the crayfish population had crashed against reference lakes where the crayfish population had been high or low over time. They found that the plants partially recovered in lakes where rusties had declined, to levels of abundance comparable to those of lakes with low crayfish populations. 

“The recovery we document potentially represents long-term ecosystem resilience of lakes to biological invasions,” the paper’s abstract says. “Our results suggest that lake communities may recover without active restoration interventions after invasive crayfish population declines…” 

The Notre Dame paper (2014) studied seed banks in the sediment of lakes with rusty crayfish invasions of varying duration on the premise that seed banks can be a source of restoration in plant communities that have been disrupted. The researchers took core samples from lake bottoms to depths of six inches and analyzed the viability of the water plant seeds they found. 

The seed bank in lakes not invaded by rusty crayfish contained more and a richer variety of viable seeds than in lakes that had been invaded. “We conclude that the seed bank has only modest potential to contribute to natural recovery,” the paper states. 

The researchers also concluded that natural regeneration of the plant community in invaded lakes would likely rely on transplanting of plants from remnant stands. Neither study can be called conclusive, but both are reminders of how interconnected lake ecosystem components are and how important it is to avoid disrupting them.

Ted Rulseh is a writer, author and lake advocate who lives on Birch Lake in Oneida County. His new book, “Ripple Effects,” has been released by UW Press. You can learn about it by visiting his website at https://thelakeguy.net.