Stay away from decay: Algae contains harmful bacteria, study says

By Lucy Schroeder

As if you needed another reason not to play with stinky piles of algae.

Decaying algae can promote the growth of bacteria that makes people and animals sick, according to recent research.

Scientists tracked the changes in bacterial communities while Cladophora algae decays. Bacteria harmful to humans and wildlife were among the many microbes they found, according to their study published in January in Science of the Total Environment.

It is possible when people come in contact with the algae or water around it they may be exposed to harmful bacteria, said Murulee Byappanahalli, a microbiologist with the U.S. Geological Survey and one of the authors of the study.

There is not yet solid cause-and-effect evidence linking human illness to Cladophora, as those types of studies are difficult to conduct, Byappanahalli said.

But even if it isn’t, the algae can be a safety hazard for people playing in water because it blocks visibility. The Michigan Department of Environmental Quality advises people to stay out of the water if they see algae on the beach, said Shannon Briggs, a toxicologist in the Water Resources Division of the department.

Cladophora is normally attached to the bottom of the lakes. During storms the algae detaches and eventually washes up on shore, forming dense mats which decompose.

“It’s just like in your refrigerator–if you leave something in there long enough, it’s going to decay,” Briggs said.

Not only do these algae masses start to smell, they also create warm, nutrient-rich environments that can host a variety of different microbes, said Richard Whitman, the retired chief of the Lake Michigan Ecological Station of the US.. Geological Survey.

The researchers found that in 24 hours the microbial biodiversity decreased in the decaying algae, according to the study. This knowledge of the changing microbial community shows the researchers whether good or bad bacteria are present in the algae during decomposition.

“Understanding this gives a better perspective of the algae in the lake ecosystem. So one important reason why we are doing this research is to determine whether the bacteria are helpful or can cause problems,” Byappanahalli said.

As it turns out, some bacteria may already be causing problems.

These mats may promote the growth of Clostridium botulinum, which is responsible for a large number of bird deaths in recent years, according to a different study conducted by the U.S. Geological Survey Great Lakes Science Center.

“The hypothesis has been that Clostridium botulinum growing on algae could be a source for botulism in birds,” said Michael Sadowsky, the director of the University of Minnesota’s BioTechnology Institute and another author of the study.

Birds may be poisoned by eating fish and mussels that have consumed the bacteria, or even by feeding on maggots from birds that have already died from botulism poisoning, Whitman said.

This is still a theory that has been inferred, not quantified, he said.

The algae is native to the Great Lakes, but has become a nuisance species in recent years because of fertilizer runoff and invasive quagga and zebra mussels, Sadowsky said.

“It may look simple, but it is a natural habitat for micro- and macroorganisms,” Byappanahalli said. “The algae is loaded with hundreds of thousands of bacteria but only small percentage may be pathogenic.”

The majority of the bacteria are helpful–without them, the algae would just sit there on the lakeshore. The bacteria are recycling nutrients in the algae and getting rid of it, Whitman said.

And that odor?

“They can’t help being stinky in the process,” he said.

The algae is also home to insects, small crayfish, and possibly baby fish, Byappanahalli said. Cladophora usually starts growing in May then begins declining in December.

In Michigan, the algal mats occur sporadically, Briggs said. But occasionally they have caused problems for beaches in the Great Lakes.

“If it’s your own private beach, you can use a rake and hand rake this stuff out,” Briggs said. If someone wants to use heavy equipment, the Michigan Department of Environmental Quality requires a permit under legislation to protect the bottomlands of the lakes, she said.

Some researchers have been focusing on the chemical products of decaying Cladophora.

“It makes a great composter,” Whitman said.