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Losing winter ice is changing the Great Lakes food web – here’s how light is shaping life underwater

Steven Wilhelm, University of Tennessee; Brittany Zepernick, University of Tennessee, and Robert Michael McKay, University of Windsor, The Conversation on

Published in Science & Technology News

Winters on the Great Lakes are harsh – so much so that the scientists who work there often focus on the summer months, when tiny microbes at the base of the food chain were thought to be most productive.

However, emerging research is changing our understanding of these winter ecosystems and shining a light on a vibrant world of winter activity just below the ice.

Scientists discovered in the early 2000s that communities of diatoms – tiny photosynthesizing algae – were thriving in the light under the wind-swept lake ice. But, it turns out, that was only part of the story.

As the Great Lakes’ winter ice disappears – it hit record lows in the winter of 2023-24 – new analyses show that some diatoms appear to have a different way to create energy and survive in the dark, turbid ice-free water until summer.

These microbes are crucial to the Great Lakes’ health. They clean the water of pollutants and are the first step in the complex food web that supports a fishery that powers part of a regional economy. Changes here can have widespread effects on the lakes’ ecology and direct economic effects on surrounding communities.

Interest in life under the ice erupted in 2007, when an international team of scientists onboard a Canadian Coast Guard icebreaker noticed something unusual as the ship worked its way through the Lake Erie ice.

 

As the ice broke, dark brown water oozed up from the lake. It was teeming with diatoms.

There had been sporadic studies of the winter microbes in the past, but limnologists – scientists who study lakes – didn’t have the tools to fully understand the microbes’ behavior until recently.

For the past five years, the Joint Genome Institute of the U.S. Department of Energy has supported a molecular biology project that sequenced the RNA of all the microorganisms from samples collected from Lake Erie to address how these organisms survived winter months and might adapt, or not, to future climate scenarios. New observations about how diatoms may be using light are now emerging from this effort.

Normally we think of diatoms as organisms that use sunlight to convert carbon dioxide into living material by photosynthesis. They’re pervasive in summer across the Great Lakes, where they help feed the lakes’ multibillion-dollar sport and commercial fisheries.

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