Scientists find culprit behind dying ‘doughnut’ of Michigan Lake

WASHINGTON - The ‘doughnut’ of Lake Michigan, a roughly circular river of phytoplankton-algae and other tiny plants, is ‘dying’ and scientists believe that quagga mussel are the culprits.

When Michigan Technological University biologist W. Charles Kerfoot and his research team first saw it in 1998, they found that zooplankton, the tiny animals that feed on phytoplankton, were much more abundant in the doughnut.

The zooplanktons were eaten in turn by small fish, which were eaten by large fish, which fueled an angling paradise productive enough to merit the nickname Lake Fishigan.

However, soon after the discovery, the doughnut started to disappear.

“Since 2001, the chlorophyll has been nibbled away on the edges, right where the quaggas are,” said Kerfoot.

The quagga mussel are introduced by ocean-going vessels when they dump their untreated ballast water and their favourite food is phytoplankton. Hank Vanderploeg, Kerfoot’s colleague, calculated that they can filter up to one third of the water column in a day in the band of water around the lake that’s between 30 and 50 meters deep, said Kerfoot. There, they are consuming five to seven times as much phytoplankton as is being produced.

That means that all the energy in the phytoplankton, which once fed fish, is being sucked down to the bottom of the lake by quaggas, who then eject it in the form of pseudo feces-mussel poop. That can stimulate the growth of Cladophora algae, which die, decompose and remove all the oxygen from the surrounding water.

“A high percent of the fish biomass could be lost in the next couple years,” Kerfoot said.

However, Kerfoot isn’t worried about is the Asian carp, which is feared to enter the water system and destroy the fishery. But quaggas will have done that job before the 20-pound bottom feeders can even get a toehold, he said.

The research has been published in Volume 36, Supplement 3, of the Journal of Great Lakes Research. (ANI)