THE CLAY FLATS --- ZEBRA MUSSELS --- SPONGES --- ROUNDED GOBIES --- CHANGES SINCE THE COMING OF THE GOBIES --- PLANARIANS --- HYDRAS AND JELLYFISH --- BRYOZOAN --- THE CLADOCERANS --- COPEPODS FROM 1993 TO 1999, AVON POINT --- DAPHNIA --- ROTIFERS AT AVON POINT
Update on the reef at Avon Point -- The Asian Carp
[To veiw the beautiful photographs that accompany this article, see http://home.centurytel.net/lakeerieecosystem ]
Lake Erie is a wilderness, a big wilderness, and it is alive. To take a hand full of water is to take a handful of life, life that lives in a different physics than we are born too.
I've pretty much given up the notion that I will ever understand at anything more than a superficial level why things occur the way do in the wave battered area of the reef, now I am content to only be a witness to its constant changes. Below the surface, in the water and at the Lake's bottom, is a world of life and a realm of simple beauty.
This report is an introduction to what I've slowly pieced together about the ecosystem found at Avon Point. I have no formal training in biological research and for the most part have had to stumble through the learning process on my own.
The only two researchers to have reached out to be of assistance (and that assistance has now faded into many years ago) are Dr. Stansberry and Dr. Beeton, both who I am indebted to for their kindness.
The reef was formed by the collapse of the shore's shale cliffs into the Lake. Over these fallen cliffs have washed rocks left by the glacier that gave the Lake its birth.
Winding through the heart of the reef is an old stream bed that has cut into the Lake's floor. Surrounding the reef area is almost perfectly flat plains of blue clay.
The reef lies on a flat ridge that surrounds the lip of the Central Basin of the Lake. The Lake's bottom drops off quickly to a depth of 10 to 15 feet and holds this depth for more than a mile out. The reef has an eerie beauty.
When diving I am able to view the reef as a bird in flight would view the land below it. Hovering over the tilted shale walls and cleaved blocks I see them not as small ridges and valleys, but rather they appear as vast western landscape seen from the view of a buzzard soaring over a land draped in a perpetual twilight of blue and green.
Scattered amid these ridges and valley are shale blocks cleaved along straight lines that give the appearance of having been the works of masons. They are like ancient fallen temples surrounded by a sacred sleeping blue.
There are two major forms of plant life living on the Lake's bottom; the laison and the long stalk algae Cladophora . The above photo is of the Cladophora growing on the rocks in summer.
The laison is a complex ecosystem that grows on the rocks upper surfaces. The laison is formed by diatom alga that, after settling on rocks, secretes a gel that not only secures it to the rock's surface but also begins to act as a trap collecting sediment as the sediment filters down from the water. The laison varies in thickness from .25 mm to 2 mm. in thickness and becomes the home to numerous small crustaceans, annelids, nematodes, insects and rotifers.
Below is a photo of the laison completely covering a rock and all the life on it. Below the laison are zebra mussels that do not seem to be affected by being grown over.
The cladophora algae are also grown over which is why it appears to look stick like. I can't tell whether the algae are able to live under this laison growth or not. The laison dies out over the winter. In the spring when I first begin diving the rocks are completely bare of all larger life forms except Zebra mussels.
I have gotten so use to viewing the world under a microscope that I had better make clear that when I talk of a large life form I thinking of living things larger than 1 mm. Usually the cladophora is the first to dominate the rocks but as the spring comes to a close and summer begins the laison begins a relentless march covering everything on rocks that lie in suitable areas.
The reef begins where Heider ditch runs into the Lake, almost directly in line with the boat launch pier. To the West is a vast expanse of blue clay, which has occasional large boulders resting on the flats, and a few small areas of rocks. To the east is the shale ridge.
Actually there appears to be either two ridges or perhaps only one that is shaped like a horseshoe with the open end facing west. On leaving shore, once past the jetties, the bottom is of clay. Between fifty and one hundred yards out the reef begins. This reef was apparently formed by the collapse of the shale cliff.
To the east, Avon Point extends out as a peninsula, but in the past the shore to the west of the Point probably lied as far out as the Point does today. The collapsed remnants of these cliffs are what make up the near shore reef.
Below, a view of Avon Point
The picture below is of the boundary area between the reef and the clay flats. The rocks of the reef on the right side of the photo are here completely covered by Zebra mussels. This density thickness of mussels is highly variable but easily 50 to 75 percent of the reef area is free of mussels.
Moving from the clay flats to the reef is analogous to moving from a desert ecosystem to a forest. What makes the reef so much richer in the number of animals and the number of species is both the numerous different types of habitats it provide and the stability of the reef itself.
Avon Point is an unprotected shore that faces one of the longest fetches of the Lake. A fetch is the distance the wind blows over open water without meeting an obstruction and the Northeast fetch is about 80 miles long.
The longer the fetch is the longer a waves length can be. And the longer the wave the greater the effect it has on the ecosystem. If a wavelength, that is the distance from the crest of one wave to the crest of the next one is 20 feet than the wave will start pulling on the bottom when the water's depth is ten feet.
I have been on the reefs bottom several times when large waves were running overhead. The current was so strong that I had to grab on to large rocks to be kept from being swept away and all around me I could here the rocks banging against each other. Any animals on these smaller rocks would be extremely lucky not to be crushed by the rocks banging against each other.
Over the years both ecosystems, the clay flats and the reef have been subject to constant change, first the coming of the Zebra mussels and most recently the arrival of the rounded gobies have vastly altered the ecosystems
Anyone who has lived at Avon Point for a long time can remember finding large clams washed up on the shore after every storm. These clams, there were five species of them, have all disappeared, killed by the Zebra mussels.
When I first started diving here it was not unusual to glide over thousands of snails of the species Pleurocera acuta. These snails are all gone now. They, as well as four other species of snails have been driven to all but extinction in this area. I really don't know what has caused their disappearance.
Other changes are only visible on the Lake's bottom such as the increase in the number of sponges, the increase in bryozoans colonies, the disappearance of planarians and on and on. In the water itself the animals that make up the zooplankton have seen their numbers diminish year after year. As I said at the beginning of these notes I can't say why these things are happening, only that they are.
The clay flats break up in many areas into what almost appears to be cut tiles with all of the life clinging to the areas formed by the gaps between these tiles.
The area in the gaps between the clay are in above picture are thousands of Zebra mussels. But in general the clay flats seem to stretch out forever like an empty desert in a perpetual twilight. In the depression in the clay in the foreground of the picture are the shells of dead Zebra mussels.In the background are boulders that harbor thousands of mussels.
THE REEF IN OCTOBER - 2000
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 surface 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. 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.
I have tried to figure out why sponges interest me so much. I think there are two reasons; one, sponges are incredibly ancient creatures, existing from Cambrian times, some 400 million years ago, and two, their whole body plan is radically different from any other animal on earth.
They are an amazingly successful group of animals if one considers the countless number of animals that have had there brief day in the sun and have become extinct. It is easy to imagine that our species too may someday no longer walk on the earth but the sponges will still be here.
The above photo is of a green sponge growing in the center of a large rock and a smaller sponge growing on the rock's edge. The larger sponge is about 6 inches in diameter.
The most important point to realize is that this green mat is one animal.Looking closely at the photo below you can see holes in the mat. These holes are the exhalant opening. Scattered over the whole surface of the sponge are much smaller inhalant openings. The sponge is one big pumping machine, taking nutrient rich water in, removing the nutrients and pushing the depleted water out.
What I like about the upper photo is that it shows the struggle the animals and plants have in finding and maintaining a place to live on. The laison, which I wrote about earlier in this report, is the brown stuff surrounding the sponge.
While the Zebra mussels found all along the rock's edge can live if the laison grows over it the sponges cannot. But sponges will kill Zebra mussels if they grow over them. The rock is one constant battleground for living space.
The reason the sponges are green is that some sponges when they grow in areas that receive sunlight are able to form a symbiotic relationship with algae.The sponge is able to get nutrient from the waste products generated by the sponge, what the algae gets, other than a place to live, I'm not sure of.
The photo below is of a sponge going into gemmule body formation. In the Fall, as the Lake water temperature begins to drop, the sponge starts to encapsulate cells in a hard cyst that will act like seeds and allowing the sponge to survive the winter and also some of the gemmules will break off and spread the sponge to new areas.
Below, a large green sponge growing on two sides of a rock (the sponge covers a 2 feet by 1 foot area). I don't know whether sponge species growing in the Lake are bioluminant, but they do seem to glow. At left are a green and a yellow sponge.
The photograph below is of rounded gobies In 1997, after the reef had seemed to reach a type of equilibrium a second great change took place, one that may be as profound as the coming of the Zebra mussels.
I'm not sure when the fish known as the rounded goby first appeared on the reef. Before their arrival a type of fish called a sculpin would occasionally be found and they, to my untrained eye, looked much like a goby.
The goby became a major factor in the reef's ecosystem in 1996. Since 1997, they are found at a density of 5 to 10 fish per square meter in the rocky areas.
The Gobies demonstrate behavior showing a great curiosity about their environment. When underwater I have held myself motionless, just above the bottom, to watch the gobies that would leave the safety of the undersides of the rocks and gather in a circle around me. At times I have counted as many as seventy-five of them. They would stare up at me from the bottom with their big bulging eyes making me feel as if I was suppose to entertain them, perhaps do a song and dance.
Their curiosity makes it hard to get a true sense at what their population density is. There is no doubt that these creatures are creating havoc with the ecosystem but they are great fun to swim with.
The following as a both an account of the changes going on the Lake's bottom and speculation on why it is happening. Bare in mind as to the question of why things are occurring I am just speculating, there is a lot of ` post hoc, ergo propter hoc` in the following.
Four of the many animals I have tried to track over the years are:
1) Triclads of the genus Dugesia,
2) five species of snails,
3) a midge larvae of the genus Ablabesmyia
4) a bryozoan or ectoproct of the genus Fredericella.
Triclads are commonly known as planarians or flatworms. They are about a quarter inch in length and live on the underside of rocks. Below is a chart of the reef's planarian population density.
See http://home.centurytel.net/lakeerieecosystem for data.
(The chart assumes that loose rocks having spaces under them for the animal to live cover the entire square meter. At some locations on the reef this is the case but it might be more accurate to divide the above numbers in half to account for the areas where rock cover is not complete)
(The picture below is of rounded gobies, note the way they all hover close to the bottom)
As is easily seen the number of planarians began declining in 1996, in 1997 this animal had almost completely disappeared from the reef. The only planarians found in the samples in 1997 were seen on Aug 26. Underwater I found planarians on two rocks on Oct 5.One rock had eight planarians the other had ten. These were the only planarians seen the entire summer.Since 1997 I have stumbled across a few planarian but their numbers are still negligible.
There are five species of snails that live on the reef:
1) Pleurocera acuta,
2) Elimia livescens,
3) Amnicola limosa,
4) Ferrissia (sp?)
5) Physa (sp?).
These animals have had a decrease in population every year for the last ten years. A sixth species that used to be found up until 1991, Gyraulus parvas, is now totally extinct in this area. When I first began diving on the reef one of the most impressive sights was the hundreds of E. livescens slowly making their way along the blue clay flats of the Lake's bottom.Every year since the population of snails has steadily decreased. This year the snails of all five species have almost vanished.
The midge larva, Ablabesmyia, lives in tubes it constructs either on the rocks surface or in the strands of the Cladophora algae that grows on the rocks. This animal is a detritus scrapper. As organic matter rains down from the moving waters unto the rocks, the midge scrapes it up and uses it for food (I think it also uses it this material, as well as it own secretions, to build the tube it lives in).
In all the years previous to 1997 the midges built most of their nest in the algae strands or in tunnels on the rocks surface. In 1997 the midges seemed to be building most of their nest on the undersides of rocks attaching the nest to the rocks itself.
(Below is a photo of the midge larvae Ablabesmyia, they range in size from 1 to 4 mm.)
Bryozoans, one of the most beautiful creatures on the reef, have also been one of the rarest of animals to find. Some summers only one or two of their colonies were found and none would appear on any of the rocks sampled.
In 1997 this changed. From the bryozoan, Fredericella, being one of the rarest creatures on the reef it has now become very common.
Why the bryozoans are now commonly found perhaps is because the rounded gobies have eaten all the planarians. Planarians are known to feed on bryozoans and with the thousands of planarians the reef once held the odds of a bryozoans colony escaping these voracious predators was slim.
Another predator of bryozoans are snails and these too have all but disappeared from the area. In the case of snails though, determining the cause of their population decline since the great mollusk die-off in the winter of 1991 is, at least to me, unknown.
Their population decline began long before the rounded gobies started living in this area and whether the gobies help hasten the snails decline is unknown. This slow disappearance of the snails worries me.
With the Unionicean clams, while I deeply regretted their disappearance, at least I could point to a cause of why they were lost. With the snails it is different. I can see no reason why they should all be disappearing and this troubles me when I wonder about the long-term state of Lake Erie's ecosystem.
The midge larvae, Ablabesmyia, display not so much a decrease or increase in population density, as they appear to have changed their reference in their selection of home sites. Before the gobies were found on the reef the midges overwhelmingly built their tubes either on the rock's upper surfaces or in the strands of the algae Cladophora growing on the rocks. Since the gobies arrival the midges appear to have shifted the site of their tube building to the underside of the rocks.
This is again, I think, is perhaps directly related to the disappearance of the planarians. The planarian species found in this area are extremely light sensitive animals and always move away from any light source. Midges that built their nest on the rock tops were then relatively safe from predation and those living in the algae strands were safer still for the planarians could not climb the algae stalks.
There appears to be two real disadvantages in living in the algae though. One is that the Cladopora, the long algae strands that is found growing on rocks and piers, as part of its life cycle, releases its hold on the rocks and drift in the open waters of the Lake.
The other disadvantage is that when strong wave generated currents sweep through the area the algae can be torn off the rocks and much of it is thrown up on the beaches. Any larvae nested in such algae are doomed.
Therefore there is a real advantage in living on the rocks surface but I can't really imagine why living on the rock's underside would be better than living on the upper side. In fact living on the top side would appear to have the advantage of having more edible organic material settling on it providing more food for the midges but with the elimination of the Planarians the midges are building far more nest on the rock bottoms then in any years since this study began.
Below is a photo of a mayfly nymph of the genus Stenonema. This mayfly is different then the burrowing mayfly of the genus Hexagenia, the Hexagenia are the mayflies that make up the vast swarms found along the Lake's shores in early summer. The Stenonema are found in far fewer numbers, they live on the underside of rocks were they scurry about like scorpions. They live for at least to years in this stage before taking their mating flights. Their bodies are between 1 to 3 mm. long and their three prong tail matches their body length.
One more point about the midges and planarians; there is a possibility the midges (and also the mayflies) will be able to increase greatly in numbers if the planarian population remains so extremely reduced. I would imagine that the planarians ate the eggs of both these insects, since planarians seem to eat anything they can subdue, so with their elimination more eggs should be able to hatch.
The changes that have been written on above cannot be thought of as negative or positive in terms of the Lake's ecosystem, they just are.
One result of the rounded gobies coming that is possible, and I have no idea how great or small this possibility may be, is a great decrease in the fish population in the Lake as a whole. This only has a chance of happening if the rounded gobies have a high population density on the other reefs of the Lake and that they eat fish eggs.
From a human point of view such a decrease in the numbers of certain species of fish would be akin to a disaster. From the perspective of a great number of creatures living in the Lake though a decrease in the fish population could either a good thing or one of complete indifference.
The crustacean zooplankton, which is preyed on by fish, would certainly not bemoan the loss of the fishery and the bryozoans would not even notice their passing. How the changes in the Lake is viewed is in many cases all a matter of what type of life form you are.
Whether the gobies have a long-term effect on this area of the Lake is going to depend on their maintaining this dense population. It is very possible that the gobies population will collapse within the next year or two.
This collapsing of population density occurred with the zebra mussels back in the winter of 1991- 1992, a population collapse from which the mollusks have never been able to recover.
I have wanted for some years to end this general study of the reef's ecosystem and concentrate on studying a very limited number of species or habitats. But whenever I think I've got a handle on the overall cycles of the reef's ecosystem nature has thrown me a wicked curve ball that I can only foul off leaving me at the plate waiting for the next pitch.
This is both frustrating and joyous at the same time. Frustrating because I would like to eventually get to first base and advance on to other things. Joyous because I'm still at the plate waiting to see what pitch nature throws me next. I can't win the game but I sure can have fun playing until death calls me out. (Below is a photo of gobies gathering around me.)
Above is a photo of an animal that belongs to the Phylum Platyhelminthes. They are commonly known as planarians or flatworms. These fascinating animals are not worms, as their common name implies, worms belong to the Phylum Annelid.
Planarians are the most primitive of the bilateral animals. These animals are small, from 4 to 8 mm. long but they are voracious hunters. The above species is new to the area. Several years ago enormous numbers of a different species of planarians of the genus Dugesia were found on the reef. They all disappeared after the arrival of the rounded gobies.
This year (2000) I am finding these animals on the rocks, though in nowhere near the number that I found the old species. In 1994 and 1995 I estimated that by July and August there could be found 300 to 600 hundred planarians per square meter on the rocky areas of the reef, by 1998 the animal had all but completely disappeared.
This new species is just beginning to inhabit the reef. These animals have an aversion to light and live on the underside of rocks. Their `eyes' a rudimentary, they are more like light detectors then organs for vision. They move by beating an enormous number of cilia (hairs) on their underside. And their `mouth' is a tube (proboscis) found about midway on their underside.
I find it interesting that if you left a planarian alone, over time it would get old and die. But if you got hold of an old planarian and chopped it up into pieces each piece would grow into a new animal and that new animal would be young. If only this would work for me.
HYDRAS AND JELLYFISH
The two animals below are members of the Phylum Cnidarians. They are freshwater hydras. These predators live on the underside of the rocks throughout the reef area of Avon Point. They are between 2 and 5mm. long and during the months from late May to July they are found on the reef by the thousands.
Members of the phylum Cnidaria have one organ unique to the phylum and that is the nematocysts. If you look closely at the tentacles seen below you can see numerous small dots or bumps running along the arms, these bumps are the nematocysts. The nematocysts are small barbs attached to a strand that is shot out of the tentacle when prey gets near any of the tentacles. The barb has a type of poison that immobilizes the prey. Paralyzed, the prey is pushed towards the mouth by the tentacle. The mouth is the bubble like structure at the center of the tentacles ring. I have seen animals half the size of the hydra itself ingested.
Hydras reproduce by budding. Below, young hydra attached to the parent's stalk. When the new hydra achieves a certain size it will break away and live independently.
The picture below is of the hydranth of another type of hydra that lives on the reef, the colonial hydra, Cordylophora lacrustris.The tentacles of these animals are not as long as those of the hydra and all of the hydranths are joined together at their base by a tube known as the hydrorhiza.
A colony on the reef may have as many as 30 to 40 hydranths and cover an area of 3 to 4 sq. cm. These colonies live on the underside of rocks. Lake Erie is one of the few freshwater bodies in the world that these animals have been found living in as they are marine (salt water) creatures.
Up until this year (2000) the colonies were normally not found until early fall, but for some unknown reason they are being found in early June. The picture below is of an unknown species of hydra (unknown to me). It is a solitary hydra, the hydranth is about 1 mm. long, the whole animal is about two mm. long. It was not found living on the rocks surface but rather it had attached itself to some organic matter living on the underside of a rock. The photo is a view of the hydra seen at 200X.
Below is a picture of a jellyfish. Since I became familiar with the animals of the Phylum Cnidaria I strongly hoped that I would one day get to see one in the Lake's water. After about twelve years of looking I have finally found one. The one below is I think of the genus Craspedacusta (though I could easily be wrong on this). It is about 2 mm. in diameter. The jellyfish was found at Avon Point on May 28, 2000.
These colonies of animals live on the underside of rocks. Each branch of the tube is an individual animal. The delicate tentacles can barely be seen in the photo on the lower left, but these tentacles are used to push a stream of water into the mouth. The water is filtered for organic matter and past out again. The entire colony on the left covers an area of about 2 cm. in diameter. The diameter of the tentacle ring in the lower photo is a little less than .5 mm.
Anyone who has come down to the Lake in the morning over the past ten years or so has probably seen me filling up two buckets of water. The animals pictured here are one of the two large groups of animals that I have been keeping track of (the other group is the rotifers, a phylum just as prevalent as the crustaceans here shown but they are very hard to photograph).
The three pictures on this page are all crustaceans known as copepods. The top photo is of the suborder Cyclopoida. This .5 mm. to 2.5 mm. animal is said to be the most numerous crustacean in the Lake. The bottom photo is of the suborder Calanoida. The calanoids are generally between 1 to 3 mm. in length.
The middle picture is a side view of a copepod showing the many legs that are invisible from the top few.These animals number in the billions when the Lake is taken at as whole. They are also very beautiful, especially the calanoid copepods.
While they are found in the Lake year round the Calanoid's population peaks in April thru June decreases in July and August, has a small increase in October and then falls to a low level for the rest of winter.
The Cyclopoid copepods follow a similar pattern, with populations peaking from May to July, decreasing in numbers until Aug. and Sept.
The bottom picture of a nauplius, which is an immature copepod. They range in size from .10 mm. to .5 mm. They are abundant from April to July and also have a slight increase in numbers in Sept. and Oct. There as been a sharp decline in the number of copepods over the years from 1993 to 1999. Why, I don't know.
This is another large group of crustaceans found in the Lake. While there are many species found my work has focus on the two most common, Bosmina and Daphnia.
The picture below is of Bosmina longirostris, an animal dear to me because it is the first animal I ever saw under a microscope when I began studying the Lake's microscopic creatures. It looked to me like a legless elephant and I had no idea such animals existed anywhere let alone in Lake Erie.
These small crustaceans are found in great numbers in the waters of Avon Point from May to July and to a lesser extant from Sept. to Nov. In the spring period the number of Bosmina can vary from zero to over 1200 per 12.5 liters.
What is really unusual about the animals found in the samples is that in one sample taken on Sunday there may only be several animals in it, on Wednesday there may be 500 to 800 animals (I take samples twice a week, usually on Wednesday and Sunday).
(The lower photo while not showing details of the little cladocerans, does give a sense of place. A three dimensional space of, to her anyways, infinite space.)
The picture below is of a cladocerana who resembles Bosmina but is of the genus Alona, this animal is rarely found in the near shore area of Avon Point.
Daphnia And Diaphanosoma are two relatively large Cladocerans crustaceans. The top two photos are of Daphnias which are between 1 and 3 mm. long and the bottom photo is of Diaphanosoma which are between 1.5 and 2 mm. long.
These animals are found from May to November usually in relatively small numbers. But there have been occasions when Daphnia has occurred in vast swarms. This swarming is one of the big mysteries I would like to solve.
A water sample of 5 liters taken away from shore had 674 Daphnia in it. A sample of 12.5 liters taken from the end of the jetty had 22 Daphnia in it. The animals where so thick in the water the water looked liked it had a snowstorm going on. How did these animals find each other? Did they follow a chemical trail? How did they manageto swim against the current? What did they gather for? Mating? Feeding? All questions I can't answer.
Most of the crustacean zooplankton are beautiful creatures, but the one below looks like something out of a horror movie. This animal is a recent invader to the great lakes and is commonly referred to as the spiney water flea. This is a large plankton animal (4 to 5 mm. in total length) .The lower picture is of the barbs found on the `tail' of the animal.
Monthly Averages for Some of the Crustaceans
Time to crunch some numbers. Remember I'm an amateur, with but a touch of knowledge of biology and even less knowledge of statistics. The numbers generated below were taken from 12.5 liters samples. The samples were taken twice a week since 1992 (though I have not been religious about getting the samples, there are a few weeks were only one sample was taken and other weeks over the years when no sample was taken at all).
When I first started this project I felt compelled to attempt to get samples year round under any conditions. This became a mission from God. After a couple of years of pounding through the ice to get to the water I gave up on taking winter samples so the continuous range of samples really extends only from April to December.
Addressing the question of methodology; I've had to make up my own method of counting the creatures. First I walk out on the stone jetties at the Veterans Memorial Park, tie a rope to a plastic bucket that I've put a rock in, toss it out and let it sink. Twelve point five liters of water from the buckets is filter through two coffee filters until about 50 to 100 ml. are left. This water is than pour into a small dish at about 10 to 20 ml. at a time and the animals counted using a dissecting microscope. I only count animals greater than .05 mm.
In case anyone is wondering why 12.5 liters is the amount of water used in the sample let me explain. I was going to use ten liters as the sample size so I figured I would measure out ten liters using two liter Pepsi bottles, trouble is a two liter bottle holds more than two liters when filled to the top, they hold about .5 liters more. I didn't realize this for several years into the study until I measured the water again using a measuring cup marked in liters. Rather than changing the sample size I just continued to take 12.5-liter samples.
In general I would say that the number of all Copepods has been decreasing over the years of this study.
COPEPODS FROM 1993 TO 1999, AVON POINT
Below are a lot of figures, which may look impressive but I caution not to read into them more accuracy than is there.I count living animals, which is hard to do since they swim fast. The more animals there were in a sample the less accurate was the count.
COPEPODS: Monthly Averages for Copepods
The following data is based on 12.5-liter samples taken twice a week. All the samples were taken in 1Gthe morning from the same location.
Calanoid Copepods, 1993 to 1999 ...
See http://home.centurytel.net/lakeerieecosystem for data.
Except for the extraordinary number of animals found on one sampling date the number of calanoid copepods would have shown a marked decline in 1997.That date was June 15. The sample had the extraordinary number of 880 calanoids in the 12.5 liter sample. The total number of calanoids found for the entire year in about 50 samples minus the June 15 date was 1130, thus the one sample had more animals than all the samples for the entire year.
I have belabored the point of the non randomness of the zooplankton in the 1996 report and so will not cover that ground again. What I want to point out here is that if the June 15 sample is dropped from the reporting than the copepods had a steep drop in their numbers in 1997 and the average for the month of June would be 52 per sample rather than 144 per sample. The average for the year would drop from 25.3 per sample to 11.4 per sample.
Whether this dropping of the sample from the total counts is valid I leave up to the reader but if the June 15 sample is ignored than the calanoids have had a major decline in 1997.
Cyclopoid Copepods: The table does not include the cyclopoid T. Mexicanus pranis. This small copepod was found very sporadically in the samples until this year. Though when it was foundit could be found in large numbers.
Comparison of Cyclopoids Copepods from 1993 to 1999 ...
See http://home.centurytel.net/lakeerieecosystem for data.
The average for July, 1999, is skewed by one sampling date (July 14) with a total of 638 cyclopoids in the sample. Eliminating the one sample from the average for the month gives a new monthly average of 23.7.
A further note on this sample: After taking the plankton sample from off the jetty I went out in a boat about a 1/2-mile from shore to get the benthic sample in about 15 feet of water. The number of cyclopoids in that 5-liter sample was 184. Multiplying this by 2.5 to make it equal the plankton sample gives a total of 460. Meaning this massing of cyclopoids in the area probably covered a large area. The cyclopoids totals taken from each sample for the month of July were: ...
See http://home.centurytel.net/lakeerieecosystem for data.
No attempt was made to distinguish between cyclopoid and calanoid copepods. I'm not sure if I could have told the difference between the two even it the attempt had been made.
Nauplii Monthly averages ...
See http://home.centurytel.net/lakeerieecosystem for data.
The Cladocerans are animals that do not lend themselves to analysis by monthly averages.They have wide swings in their population density from sample to sample.It is as if they move in swarms, though a far better study than this would have to be done in order to prove that.
A case can be made though the Cladocerans are not members of the plankton if a strict definition of what planktonis is used (a case can be made that the copepods are also not strictly planktonic, a view that seemed to be held by G.E. Hutchinson who referred to them as nekto-planktonic. The numbers forthe graph below were generated by the same 12.5-liter samples described earlier ...
See http://home.centurytel.net/lakeerieecosystem for data.
What clearly is shown by the graph is that Bosmina has an increase in density in Spring and Fall. What I can't make heads or tails of is whether there is an increase, decrease, or the same population density over the years. Below is a graph of an Bosmina over a one year period.
Below are graphs for the other major cladoceran found at Avon Point, Daphnia. These numbers are also hard to interpret. They show an increase in density in the spring and a smaller increase in the fall. Like the Bosmina the numbers widely fluctuate from sample to sample.Again,either from my lack of knowledge of statistics or because the data is insufficient I can not tell whether there has been an change in the number of Daphnia over the years or not ...
Before leaving the Genus Daphnia I would like to give data regarding swarming of these animals. Below are notes concerning two dates when swarming was witnessed. The data here brings up a whole range of fascinating questions concerning the movement of zooplankton in the water.
August 27, 1995. The time was between 9 and 9:30 in the morning. Being underwater I can only estimate that the sample was taken somewhere between 100 yards and 1/4 mile from shore. There were no waves. The animals, like in the July 13, 1994 sample, could be seen as a white cloud in the water. Sample was taken in 10 to 12 feet of water. The swarm was no more then 10 feet wide, but I have no idea how long the column was.
Aug. 27 1995 5 liter sample Crustaceans
Daphnia retrocurva 340
Calanoid copepods 20
L. kindtii 14
Tropocyclops prasinus mexicanus 123
Cyclopoid copepods 75
Rotifers Polyarthra 2
Plankton sample: Regretfully I wasn't able to take a plankton sample on the 27th but did take one on the 26th, so the comparison is not as strong as the sample taken in July of 1994.
I think the plankton sample still strongly points to swarming behavior of all of the crustacean zooplankton except for T. mexicanus ...
ROTIFERS AT AVON POINT
This link explores the members of the phylum Rotifera found in the waters of the reef. This section is very incomplete for a number of reasons. Two of the most prominant are that I only am able to deal with animals greater than 0.10 mm. with any confidence, and that because the rotifers that live on the substrate are difficult to see with the equipment I use they are totally absent from the data. This is unfortunate because I suspect they occur in large numbers.
The above link is a rough attempt to show the vast quanity of animals living in each cubic meter of water found at Avon Point
This link concerns itself with the number of hydras and the Protozoans known as Peritechs .
CONCLUSION: There is no conclusion, the more data I collect the more the Lake's ecosystem remains a mystery to me. And the mystery, after all these years, keeps alive the sense of wonder, and the humbling beauty that is life in all its forms.
LETTER TO THE EDITOR of The Morning Journal, 12-02, By John Lavelle
``Studying Lake Erie's ecosystem and observing the Lake as it has changed over the years I've often made predictions on what changes would take place from year to year. Nine times out of ten I am wrong. That tenth time, when I've guessed right, I've come to look at as a chance hits, like a person shooting a lot of bullets at a target; shoot enough lead and one is bound to hit the bullseye.
What follows is not a scientific explanation of Lake Erie but rather the fun I've had coming face to face with world I didn't know existed and the joys of exploration.
I have no pronouncements on what the state of the Lake is or will be, no remedial plans. What is written here is a view of a small section of the Lake known as Avon Point I write this now because so much is written these days about this committee or that commission; about action plans, strategic plans, long term plans; about the need to study this and the need to research that; none of it deals with the Lake I have known for so many years.
Now the Lake faces the threat of invasion of the giant Asian carp. I'm of two minds about their coming, both totally selfish. On the one hand I dread their arrival. The carp that currently live in the Lake are frightening enough. There was a school of large ones living east of the last pier at Veterans Memorial Park. I haven't seen them for several years. Perhaps they have moved on or died.
I hated Scuba diving with them around. They had the nasty habit of following several feet behind me. I could never see them clearly. They would hang back behind me eerily stalking me as I swam along. This new larger carp will scare the dickens out of me if they follow the habit of their smaller cousins. But while I dread there coming for that reason I am ashamed to admit that their arrival would certainly stir up the ecosystem.
I've mucked about the Lake's bottom Lake Erie as an amateur naturalist for over ten years and in that time the Lake has gone through so many changes that the ecosystem is almost totally different from what it was when I first started exploring. If I compare the number of species of animals found on the Lake's bottom now with those found ten years ago the lose of diversity becomes striking.
Before the arrival of the Zebra mussels there were five species of large native clams living in the Lake; the mussels drove them to extinction. But the most profound changes occurred several years later, after the arrival of the small fish, the rounded gobies.
Before the gobies settled here the small reef that lies about a hundred yards from shore and the clay flats that surround it was home to an enormous number of snails. With in two years of the gobies coming all five species of snails disappeared. This was not a small number of animals, the snails could be found on the reef numbering in the thousands.
Also disappearing from the bottom was an animal commonly known as a flatworm or planarian. These animal had an enormous population on the reef, easily numbering in the ten of thousands. They too after the gobies arrival disappeared.
Both the flatworm and the snails were predators on a group of animals known as Bryozoans. These animals, while the snails and planarians lived the reef, were extremely rare. Now with their disappearance the Byrozoans population has increased tremendously. Its almost as if every third rock has at least one colony living under it.
There were three major groups of insects living on the reef; two of them, the mayfly and the midges are familiar to almost everyone but there was a third group,the caddis flies, that also made up a large portion of the insect population. There were six or seven different species of these insects, though the net builder, Hydropshye was by far the most numerous; all the caddis flies have disappeared.
Why the mayfly and midge population should remain and only the caddis fly should become extinct is just one of those mysteries beyond my ken.
Over the last two years the reef has achieved a balance. The rounded gobies are as numerous as ever. It is very hard to get a sense of the number of these animals for these critters seem to have an innate sense of curiosity. When I remain motionless on the Lake's bottom for a few minutes they come swimming out from under the rocks gathering around me in a circle. I've counted seventy-five at a time staring up at me.
Anchors are also a big attraction to them. Let an anchor rest on the bottom for a few minutes and twenty to thirty will gather around it taking stock of the new arrival on their premise.
Zebra mussels have also achieved an equilibrium. After their initial assault on the reef, a time when after their spawning young mussels would be as thick as sand in the cracks in the clay flats that surround the reef, they've reached a stage where at least ninety-five percent of the reef is free of them. The rounded goby does not appear the reason for their population decrease as the great die off of mussels occurred years before the their coming.
There are three other groups of animals that play a large part in the ecosystem of the reef that still have great fluctuations in population: sponges, peritechs, and hydras.
For sponges, and I'm only guessing here, the great determining factor governing their population seems to be water clarity which fluctuates widely from year to year. Over the last two years the clarity has diminished and so has the number and size of the sponges.
The Zoothamniums, are a genus that falls in a group of one celled animals known as Peritechs. They are large for one celled animals being between one half and three quarters of a millimeter in size. The zoos live in colonies that cover only about three fourth of a cubic millimeter, but what they lack in size they can make up for in numbers. In early spring these colonies can number in the millions on the reef if the conditions are right. Problem is I have no idea what are the right conditions for their growth. Some years they are everywhere, others years they are not. For reasons totally unknown to me they almost all disappear by the middle of June.
The hydras are also animals that in some years are found in great numbers in the spring on the reef, and also, like the zoos, they can all but disappear by June. While they don't even come close to the number of the zoos found, in a good year for them almost every rock with space under it will have say five to ten animals on it. And while they don't have the great numbers the zoothamniums have they are much large in size, their stalks measuring around five millimeters in length with their tentacles also being about that long.
As anyone who has any knowledge of the biology that lives in the Lake knows I've not touched at all on that great group of animals the crustaceans. There are several reasons for this, but the primary one is that I have no idea how to measure the population of these every shifting creatures.
I have taken water samples for years and counted the number of crustaceans in these samples. The more data I gathered the less sure I was that the information gathered gave any accurate reflection of the populations of the various animals over the years. From what I've seen of the type of research done on the zooplankton in the Lake I've come to believe that no one really knows how these small animals behave and almost every study done has been waste of time if someone is trying to determine whether the various populations are increasing or decreasing.
All of this bring me back to the coming of the giant carp. As things stand now the Lake's bottom is getting to be a boring place. There are fewer and fewer species to take an interest in. So from my point of few, the totally selfish one, the carps coming might prove interesting if they were able to knock down the population of rounded gobies and allow some of the old species to return to the reef.
Even worse, I sin in thinking it might not be so bad if some freighter dumped some other interesting critters into the Lake with it's bilge water. The Lake has lost so many species that there has got to be some large niches to fill.
Granted any change in the Lake by species introduction is a crap shoot; especially when it comes to the effect it will have on the sports fish population, but I haven't fished in years. Since I began diving I've struck a deal with the fish that live in the Lake; I won't take them out of the water if they don't keep me in it. So far the deal has worked well for both of us.''
See http://home.centurytel.net/lakeerieecosystem for more information.
HISTORICAL SKETCH OF AVON, OHIO, TO 1974