Everybody was talking about zebra mussels when I left Chicago in the fall of 1993, but you generally had to look underwater to see any. By the time I returned early this year the presence of those tiny, alien mollusks was apparent to anyone paying any attention at all.
Gobies are a varied bunch–only one other family of fish has more species–but they tend to be small. Only a few species reach a foot in length. Most are less than six inches long, and one, which lives in the Philippines, is less than a half inch long, making it the shortest vertebrate in the world.
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The gobies have been greatly helped by the large increase in the amount of rocky shoreline on the lakes. Chicago’s step-stone revetments make excellent round-goby habitat, as do the miles of shoreline we have heaped with jumbled rocks to reduce erosion.
You might think that was good news, and in a way it is. However, it does not solve the zebra mussel problem. A healthy population of round gobies might mean that zebra mussels would cover only 75 percent of the available substrate rather than 100 percent, but we would still have a whole lot of zebra mussels.
Meanwhile the zebra mussels are feeding away. There is evidence that they feed more selectively than we might suspect. They love green algae, but they don’t care much for blue-green. We are beginning to see population explosions of blue-green algae in some places. Most of the tiny algae eaters native to the Great Lakes don’t like blue-green algae either. What happens if zebra mussels gobble up the base of the whole food chain? At this point, nobody knows. And the only way to find out is to have it happen.
