Going blind: Algal blooms make it harder for walleye and other fish to see under water

Water pollutants aren’t just limited to toxic chemicals and metals. Excessive amounts of algae will turn the water so murky that fish will not be able to see through it. In a Newswise article, researchers warned that these harmful algal blooms could threaten the populations of important fish like walleye.

In a recently published study, Ohio State University (OSU) researchers compared the effects of algae and sediment on the vision of fish. These two different materials are often the reason for the murkiness in the waters of Lake Erie.

They found that algal blooms reduced the eyesight of the animals more than an equal amount of sediment did. The algae could decrease visibility by more than 40 percent.

OSU researcher Suzanne Gray headed the experiment. She served as the lead author and published the findings in the journal Conservation Physiology.

This is a big deal because most fish rely on their eyes to survive in the wild. When they look for food, mates, or predators, they will use their eyes by default.

“This is concerning for these important fish populations. If we can’t get a handle on algal blooms, this could threaten their well-being,” explained Gray. (Related: We can prevent shoreline erosion by protecting coral reefs: Restoring them helps protect islands.)

What is easier for walleyes to see through – algal blooms or sediment?

In their experiment, the OSU researchers placed single walleyes and emerald shiners in round tanks of water. A screen with a pattern of alternating stripes encircled each tank.

This screen would rotate slowly. If the water were clear enough, the fish would be able to see the screen and learn the pattern. It would then swim in circles to match the movement of the stripes.

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Over time, the researchers added more and more material to the water. They used actual sediment from Lake Erie or emulsified spinach as an algal simulator. The vegetable shares the same color, size, and light-scattering properties as many common species of algae.

Every time they added sediment or spinach, the researchers recorded any changes in the activity of the fish. If the fish stopped swimming in synchronization with the patterns, it meant the animals could no longer see the screen due to the cloudiness in the water.

The researchers made sure that the turbidity of sediment and spinach were the same. They compared the amount of each material needed for the fish to lose sight of the screen.

Algae clouded the eyes of fish much worse than sediment

Gray and her team reported that both walleye and emerald shiners were able to see better through water clouded by sediment as opposed to spinach and algae. The eyes of the fishes could handle muddy water, but not so much with clouds of algae.

The researchers noted that both species live in waters that often become muddy. Walleye are most active at dawn and dusk when they hunt emerald shiners for food. The murky water and time of activity have led to both species developing a lowlight vision.

“But algae is different,” Gray noted. “It’s green, and it changes the light. It could be that both the reduction in light and the change in color inhibits vision differently than sediment.”

Harmful algal blooms are increasingly common in Lake Erie and other bodies of freshwater in the United States and the rest of the world. When Gray started her study in 2014, Toledo’s public water system was contaminated by one such bloom. The OSU researchers stressed the importance of figuring out how these blooms are harming fish populations.

Learn how you can help preserve walleyes and other valuable fish species at Ecology.news.

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