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Readers Want to Know…

Clump of sand with the goo balls.

Mysterious goo balls (shown here on sand) baffled Lake Superior beach-goers this summer.

What are those small goo balls that washed ashore on beaches around Lake Superior?

Several readers contacted us in August about mysterious pea-size blobs of gelatinous ooze they found in different areas of Lake Superior. Reports came from Michipicoten Bay in Canada, the Keweenaw Peninsula in Michigan, the Bad River area in Wisconsin, and Minnesota Point (known locally as Park Point).

A similar goo outbreak occurred on Park Point in 2001. Then, researchers from Sea Grant, the University of Minnesota Duluth, and U.S. Environmental Protection Agency identified the transparent blobs as a natural occurrence — remnants of a zooplankton called Holopedium gibberum. The outbreak this summer was due to the same species. However, unlike in 2001, this “bloom” of blobs seemed more widespread.

Scientists aren’t sure why Holopedium are more abundant during some summers than others. They are often found with spiny waterfleas (Bythotrephes longimanus), leading scientists to suspect this invasive species benefits the native Holopedium, perhaps by eliminating competition for food.

A Holopedium gibberum inside its mantle.

A Holopedium gibberum inside its mantle. Photo courtesy of Jim Haney University of New Hampshire

View a movie of a Holopedium gibberum feeding, courtesy of the Center for Freshwater Biology, University of New Hampshire.

What they do know is that adult Holopedium live in a mucous mantle (of their own making) that encases a pea-sized amount of water. Their legs stick out of the mantle allowing them to swim. When in residence, they often form globby groups as their mantles adhere. The mantles may provide protection from predators or buoyancy control for their feeding behavior, which involves migrating towards the surface near sunset and returning to the depths during daylight. At some point, perhaps to breed, the zooplankton leave their homes and brave the open water. The biodegradable mantles (composed of one or more acid muco-polysaccharides) then float or are blown ashore.

The mantles are difficult to see in the water, but swimmers often feel them. “They bumped into us as we swam,” said Cindy Hagley, an environmental quality extension educator for Minnesota Sea Grant who encountered the tiny beasts off the Keweenaw. “It felt like swimming through thousands of tiny bath beads.”

Holopedium gibberum are found in the basins of the Great Lakes and many inland lakes and reproduce both sexually and asexually. They also live in northern arctic lakes in North America and Europe.

So never fear, they’re not a tapioca spill, or disposable diaper material — just nature at work.

By Sea Grant Staff
October 2006

Return to October 2006 Seiche

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