ZEBRA MUSSELS - LAKE ERIE - CENTRAL BASIN - AVON POINT
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.
ZEBRA
MUSSELS
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 mussels’ 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.
