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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.

Walking on Hollywood Beach on early spring mornings, I noticed that a strip of sand about a foot wide at the water's edge was carpeted with a layer of striped shells, the earthly remains of dead zebra mussels. The lake bottom in the city's harbors, which had not been visible from the shore, could now be plainly seen. Zebra mussels are filter feeders, which strain algae and zooplankton out of the water. Their massive presence makes the water much clearer.

The ultimate effect of zebra mussels on the Great Lakes is unknown at this point, but it will probably be harmful. And of course there's something else to worry about: gobies. In particular, round gobies and tube-nosed gobies, the latest additions to the ever-weirder fauna of the Great Lakes.

Gobies, members of the family Gobiidae, are found in salt or brackish water pretty much all over the world. They mainly stick close to shore in shallow waters, and their tolerance for brackish water--water that is salty but less salty than the open ocean--helps them live at river mouths and in estuaries where salt and fresh water meet.

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.

The family includes such intriguing species as the mudskippers, a pop-eyed little fish that lives in the tidal zone among mangroves on tropical coasts. These fish stay put when the tide goes out, skating around on the mud and living quite happily out of water for hours at a time. Several species of blind cave fish are also gobies.

The two pelvic fins of most gobies are fused along the belly to create a suctorial disk, a sort of suction cup the fish uses to keep itself solidly anchored to the bottom even in very active waters. Our two new gobies especially like rocky shorelines where there are lots of places to hide. They lurk under something during the day and come out to feed at night.

The Great Lakes gobies were first discovered in 1990 in the Saint Clair River, which connects Lake Huron with Lake Saint Clair. The gobies probably came here from the Black Sea in the ballast water of a freighter. They are excellently adapted to such transport since they seek out holes and crevices to hide in, they can feed in the dark, and they can tolerate water with low levels of dissolved oxygen. They might even be able to hitch rides on the outsides of ships. If a dent along the seam between two hull plates got bent a bit and opened up a tiny cavity, a goby could swim in, anchor itself to the hull, and hang on.

Hitchhiking may account for the lightning speed of the round goby's colonization of the Great Lakes. Since that first sighting in the Saint Clair River just five years ago the tube-nosed goby has not spread, but the round goby has turned up in Lake Erie; in the Welland Canal, which connects Lake Erie and Lake Ontario; in the southern end of Lake Michigan, where it is already abundant in suitable habitat; and in the Duluth-Superior harbor in Lake Superior. It took alewives decades to get that far.

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.

Since the gobies, like the zebra mussels, came from the Black Sea, the freighter they rode on was probably Soviet. According to David Jude, a research scientist with the Center for Great Lakes and Aquatic Sciences at the University of Michigan who has studied the gobies, it is conceivable that the gobies arrived on the same ship as the zebra mussels.

Coincidence? As a cautious, careful scientist, David Jude is not going to make any claims--in fact, I never asked him to. But as a crusading journalist, I'm not going to back away from possible controversy. Could it be, I asked myself, that the Russians--having already employed sex, drugs, and rock and roll to demoralize America's youth--are now going after our water supply?

Then Jude mentioned that the round goby is widely used for food in the "former" Soviet Union, and the whole thing became clear. The gobies are an advance supply drop--food ready and waiting for the moment Russian troops, under the command of the United Nations, move in to occupy a defenseless America.

One round goby wouldn't make much of a meal. The largest of them grow no longer than nine inches, but you could probably fry them up in batches like smelt. The really strange part is what they eat. Small round gobies, up to about 2.5 inches, eat a variety of insect larvae and zooplankton, but as they approach three inches in length they feed almost exclusively--the best estimate is 90 percent of their diet--on, you guessed it, zebra mussels. One healthy round goby can consume nearly 80 mussels in 24 hours.

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.

You might also find yourself humming the song about the old woman who swallowed a fly and then a spider to catch the fly and a bird to catch the spider and so on until she swallowed a horse and died.

Consider the fate of the mottled sculpin. This is a small native fish that prefers rocky shorelines. When it is not actively feeding it hides out under rocks. When it spawns it builds a nest for its eggs in one of its typical hiding places. Its way of life, in other words, is almost exactly like that of the round goby. Where gobies have become abundant, mottled sculpins have virtually disappeared. A small fish called the logperch has been similarly, if less drastically, affected.

The next question is: Is there anything that depends on mottled sculpins? Will we realize ten years after the sculpins are gone that we aren't seeing some other species that existed in a symbiotic relationship with them? Part of our problem in these areas is that we are used to thinking in terms of very short stretches of time. On the commodities markets they think in terms of minutes or even seconds. Companies that develop new products think in terms of a short span of a few years from idea to introduction. Presidents serve eight years at most, and even Supreme Court justices seldom last more than a couple of decades.

Ecological cycles last much longer. Alewives have been in Lake Michigan for more than 30 years, and their story is still unfolding. It is even possible that they could disappear from the lake. We added alien predators like the coho salmon just 20 years ago, and we are a long way from knowing the effect they will eventually have. Right now the Great Lakes are like a very poorly designed experiment set up by an incompetent scientist who figured that 600 or 700 variables would be just about right for his protocol.

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.

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