The rapid spread of non-native mussels in the Great Lakes has caused an unprecedented ecological shift in lakes Michigan and Huron, stripping the massive freshwater lakes of life-supporting algae, according to a new study by University of Michigan researchers. Whilethe increased number of zebra mussels has been observed in the lakes for decades, an even greater threat in recent years has been the spread of the closely related quagga, a fingernail-sized mussel that thrives in the lakes’ deep muddy bottoms. Each quagga mussel, billions of which now blanket the bottoms of lakes Huron and Michigan, filters about a quart of water daily, and feeds on algae that is a critical food source for other lake organisms — including the shrimplike Diporeia, which has long been a pillar of the Great Lakes’ food chain. Researchers say algal production in both lakes in 2008 was 80 percent lower than in the 1980s, a phenomenon that coincided with the spread of the quagga. “These are astounding changes, a tremendous shifting of the very base of the food web in those lakes into a state that has not been seen in the recorded history of the lakes,” said Mary Anne Evans, lead author of the study, which will be published in the journal Environmental Science & Technology.
Michigan Sea GrantA quagga mussel