Linking Invasive Mussels to Algal Blooms

In the late 1980s, the zebra mussel, a small species of mollusk, jumped from the frigid waters of Poland and modern-day Russia to find a new home in waters leading to North America’s own Great Lakes. Zebra mussels, and the closely related quagga mussels, quickly proved themselves to be a formidable threat; they might be smaller than a fingernail, but they’ll happily coat every surface (nonliving or otherwise- they won’t discriminate between colonizing a rock and a clam) and drive native species from their waters. In the past few years, countermeasures have been taken, but these are difficult and expensive to implement, and in many cases seem to be futile. Zebra mussels hopped the Atlantic to get in these lakes, and they don’t seem to have any plans on moving back.

zebra mussels

Image courtesy of NOAA

Zebra mussels have been a problem in the Great Lakes, and other water systems in the US and Europe, for decades. So, you may ask, besides another harmful invasive species swimming through our waters and killing off the native fish, what’s the problem here?

The answer is algae.

Algae are protists – primarily single-celled organisms that have many of the characteristics of plants. We have all seen algae on area lakes and streams. They may seem harmless, but some forms of algae pose more of a threat than many people realize. Some release harmful toxins; in 2010, at least three dogs died from swimming in or ingesting algae-ridden water. Even the more benign species can pose a threat. When exposed to ample food and sunlight, algae colonies can grow from small patches on a lake’s surface to huge, thick mats of plants that both reproduce and decompose at extraordinary rates, the latter of which sucks precious oxygen from the water beneath. As a result, algae blooms tend to kill fish and any other organism with the bad luck to be swimming through its same waters.

The same kind of algae that killed pets in 2010, as referenced above, was the culprit of the recent two-day water ban in Ohio. A type of blue-green algae, called microcystis, swarmed Lake Erie, releasing a harmful toxin called microsystin, which can cause headaches, dizziness, and liver damage in humans. While the bad was short-lived, it is a sign that the ecology of the Great Lakes is in trouble. And the situation in Lake Erie wasn’t an isolated case; scientists warns of several other places that could soon experience similar problems.

lake erie algal blooms

image courtesy of NOAA/ESA

But what do mussels have to do with this?

Originally, it seems like the answer would be “not much.” Zebra and quagga mussels actually feed on algae, which, in this context, seems like a good thing; the problem is that they’re feeding on the wrong ones. These mussels will happily eat the algae that forms the foundation of Erie’s food chain, but they won’t touch harmful ones like the blue-green microcystis that are producing the toxin. With less competition, the blue-green algae thrive. Also, the mussels release phosphorus as a waste product, the same element in many fertilizers, which send the algae populations skyrocketing.

Mussels are far from the only cause for the increasing frequency of algae blooms. Climate change and global warming play a part, (since these particular disasters seems to have their fingers in all the poisoned pies nowadays). One consequence of climate change are fluctuations in precipitation patterns, with some areas experiencing droughts and others intense downpours.  In the Lake Erie region, the increased rainfall means increased runoff, and algal blooms thrive on the fertilizers that wash in from nearby farms. In addition, overall water temperatures are slowly rising, causing algae blooms to not only occur more often but to last longer when they do. For fish, this is a very nasty turn of events- and, as it’s turning out, for humans as well.

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