Below, a view of a rock that's side is completely covered by Zebra mussels. I
would estimate there are between 500 to 1000 of them. 
Below are hundreds of Zebra mussels living on the surface of a round rock. For some reason they will only occupy an entire rock's surface
only if that surfaces is curved. 
In 1989 I was working on an archaeological problem that was stymied until some fragments I had found were examined in England. I thought while waiting I would try to answer a little question concerning mollusks.One of the most common snails found in the Lake back then was the species, Pleurocera acuta, who has a pointed shell that has variety of colored bands running horizontal to the apex. Why the colors, I ask myself, and how many different colors are there? My daughter and I were gathering samples of these shells on the beach when she found a small, about one quarter inch long, flat bottomed clam shell and presented it to me. This turned out to be the first zebra mussel shell I had ever seen and was to lead me into being swept up in the panic that was to grip freshwater biologist for years to come. 
The photo below is of Zebra mussels living in a towering cluster.
                              Why they do this I don't know. The cluster is 3 to 4 inches high. 
In the Fall of 1989 I noticed the cracks in the clay were full of what I thought was black gravel. This gravel turned out to be young mussels, millions and millions of them.This project was started because of the Zebra musselsí invasion into the area of Avon Point. I, like so many others, was dumbfounded by the fantastic way these little critters multiplied. The Lake I knew from years of diving in the area on the archaeological project was being lost to these little creatures that had come from a distant sea. I decided to discover what changes the mollusk would bring to the ecosystem. As quickly as I started I stopped. Even a cursory glance at the scientific literature was enough to frighten me away. The Lake is full of really bizarre animals living in a complex way that was totally foreign to anything I had experienced. These animals in both looks and lifestyle may as well have been on another planet for all I knew about them.
One Sunday, in the fall of 1990, my son and I were scuba diving about a mile from the shore of Avon Point. Below us, scattered about, amid the flat blue clay and rocks, were the large native clams of the Lake. These clams, growing to about four inches in diameter were beautiful to see living on the Lake's bottom. With shells open about an inch and their siphons extended their inner chamber seemed to glow with a pale green light. Wondrous too was watching a clam walk along the bottom. With it's long single "foot" extended in front the clam pulls the shell forward. I've been struck watching them moving to ask, where is that they are going and how will they know when they get there? These mollusks have nothing that we can call a brain, or rather, in long evolutionary time the brain has scattered itself all over the clam's body. There is no one place you can point to and say this is the main seat of thought. Nor do these clams have eyes in the sense that they can see. They do have points on the outer edge of their mantle that are light sensitive, but in walking they seem to use their foot the same way a blind person uses a cane. While admiring the clams below me on that Sunday the realization struck that all of these clams were doomed. Attached to the open edge of the shells I could see hundreds of small and large zebra mussels. Both these clams, the zebra mussels and the native species, eat by filter feeding. With one siphon they draw in water and using a unique organ called the ctenidia they extract both food and oxygen before expelling the filtered water with the other siphon. With the hundreds of small zebra mussels attached to their shell the native clams were not going to be successful in competing for food. This realization struck me while I was thirty feet underwater and I immediately began grabbing every clam and cleaning the zebra mussels from their shells until I forced to surface because the air supply had run out. Over the winter of that year I obtained a permit from the State of Ohio to continue with the clam cleaning. I found out that all native clams are all protected as endangered species, thus a permit is require to handle them. I began searching again for the clams in the spring of 1991. I was too late. They were all dead. Five species of what are known as Unionicean clams had been driven to local extinction. In the 6 years since I have only seen one living Unionicean clam, that was in July of 1991, since then no living native clam has been found. In some strange way I feel personally responsible for their demise. Without doubt the chance of my succeeding at keeping the clams alive even for a little longer were remote at best even if I had more time before for their disappearance. Some would also question whether there would be any value in keeping them alive longer since their long-term prognosis offered almost no hope. But in my mind, my guilt arose from ignorance, ignorance born from the laziness of not being willing to take on the task of learning about the ecosystem I was spending so much of my time in. Growing out of that sense of guilt has grown this project of trying to understand how the Lake's ecosystem works on the shale reef. 
The photo below is again a collection of mussels living on a curved rock 
The photograph below is to show that while there are millions
of mussels found on the reef most of the area is completely
devoid of them. 
In 1999 there was no spawning of the zebra mussels, at least I found no evidence of it happening on the reef. This year (2000) the spawning has taken place, beginning in September.