HYDRAS AND PERITECHS
As far as I know this is the first time a quantitative study has been attempted for population
densities of both Hydras and Peritech in any of the Great Lakes. In both cases I do not want to imply a
greater degree of accuracy than is the case. When the rocks underside area was determined I treated
the rock by it's general shape. That is if it looked basically like a rectangle, circle, or triangle the
area was figured as if it were that shape. Also I rounded the rock sizes to the nearest centimeter. In some
cases in 1993 and 1994 I did not make actual counts of the animals only an area of the rock and had to
extrapolate the total from this.

Hydras
From the general characteristics of the animals I think that these are Hydra americanus (but I could
be wrong). The following tables shows the Hydras population peaking in June of every year. In 1993
and 1995 there was a smaller population increase in October (1993) or September (1995). Every year the
density of the Hydras has been decreasing. A shotat speculation would be that the hydras are decreasing
because of the decreasing numbers of crustaceans
Average monthly population density for hydras. The numbers are the average number of hydras per square cm. The rock under surface area is only the area of the rocks taken into account, not included are the rocks sides which may also have a large population of hydras. The hydra were only rarely found on the rocks upper surfaces. The figures were derived from about sixteen samples per month (far fewer
samples were taken in the months of April and Nov.).

HYDRAS PER SQUARE CM.
                    1993            1994          1995           1996          1997          1998
April                                   0                                                                     0
May             0.078          0.0007       0.0016              0              0                0
June             0.203          0.2318       0.4069              0.134        0.067         0.158
July              0.281          0.1123       0.1393              0.093        0.051          .008
Aug                 *              0               0.0091              0.007        0.012        0.002
Sept                 *             0.0016       0.0476              0.014        0.014        0.0008
Oct               0.383          0.0034       0.0254              0.012        0.022        0.0044
Nov.                                                                                         0              0.006

* for these two months the hydras were extremely rare.
 
 

Green Hydras
In the past 6 years I have only run into these animals twice.

July 16, 1995 one animal seen. The green hydras' stalk was 2 mm. long and the 5 tentacles were about 1/4 the length of the stalk.

August 17, 1997. Very short tentacles about 1/4 the stalk length.
 

Zoothamniums

Since these animals, the "Peritechs" are so little known to people who are interested in the Lake's biology
I thought a brief description would be prudent to put here. None of the following is derived from my work. All the information except that dealing specifically with Avon Point is from the sources listed below this introduction. The two species Zoothamnium and Carchesium belong to the order Peritrichida.
The Peritechs are found in a wide variety of environments and while the Peritechs as an order can be solitary or colonial, sessile or mobile, stalked or free-swimming, we are concerned here only with the colonial sessile members of the order. The colonies of the Zoothamnium found at the Point are palm leaved shaped colonies between 1 and 2.5 mm. in height and about the same size in width. Normally the
Zoothamnium are symphorionts to other benthic animals, but here on the shale reef, the colonies,
while sometimes found on Zebra mussels, the vast majority are attached to the underside of rocks.
Most of the species are bacteria feeders. A bell shaped like vessel is attached to the substrate by means of a stalk, all of the stalks are connected together. The stalks being thus joined together are not independently contractile, the whole colony contracts at the same time. This not true of the Carchesium, which is also present on the reef. The Carchesium's stalks while they join together to form a colony remain independent of each other and each stalk contracts individually. The colony expands by fission, the fission taking place in a definite way giving the colonies of each species a definite shape. The colonies are founded by large bells which detach from the colony and swim away. After swimming for several hours they attached to the substrate and grow a stalk, beginning a new colony. Normally the colony remains active until November or December and then produces a resting cysts to over-winter. Here, at Avon Point, the colonies all but disappear in June and do not reappear until the following Spring. The Carchesium differs from the Zoothamnium in shape, they are not palm-leaf shaped rather they are shaped like a funnel.
Sources
Tom Fenchel. "Ecology of Protozoa" 1987 (Brock/Springer series in contemporary bioscience)
Science Tech. Inc. Madison Wisconsin. Page 6.

Parker, Sally "Synopsis and Classification of Living Organisms".
Page 628 - Subclass - Peritricha.

Libbie Hyman " The Invertebrates" ; Protozoa through
Ctenophora". 1940 McGraw-Hill New York

V.A. Dogiel " General Protozoology" 2nd Edition 1965
The Clarendon Press Oxford (Pages 285,278-80,464,471)
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ZOOTHAMNIUMS PER SQUARE CM. ON ROCKS UNDERSIDES
 

                       1994            1995          1996          1997          1998
April                  +                                                                   0.09
May                 1.41            0.12           0.28           0.955         0.45
June                 0.03            1.3*           1.42           1.62           0.004
July                  0                0                0.09           0.049         0.02
Aug                  0                0                0.08           0.445         0.042
Sept                  0               0                0.03            0.204         0.064
Oct                   0               0                0                 0.218         0.045
Nov                  0               0                                   0               0

+ The Zoothamnium were found abundantly in this month but, regretfully I didn't count the entire number of colonies found on the rocks. Instead I took samples of using of a area of the the rocks underside. This
was a mistake in hindsight (but than how was I to know I was going to keep doing this for four years).
The notes do tell that rocks were found with 11 zoothamnium per roughly an area of 30 mm.sq. at their
densest and 2 zoothamnium per 30 mm. sq. elsewhere on the rocks.

* The Peritechs were only found on two rocks in June. The following table lists all the rocks sampled
for the month. The second rock of June 1st had an extraordinary number of colonies but after that
date not a single colony was seen. Below is an example of how the Zoothamniums abruptly
disappear from the Lake's bottom and it also shows how the colonies are not uniformly found on the rocks. These colonies some to have a preference for certain rocks. What it is they prefer I have no idea.
 

               Area                             Number
             Sq.cm                           of colonies
June 1        48                                51
               110                               1460
June 7        99                                  0
                 44                                   0
                 40                                   0
June 11     70                                    0
                153                                   0
Jun14       112                                   0
                 54                                    0
                 40                                    0
June 18      85                                    0
June21       88                                    0
                 30                                    0
June25       48                                    0
                 77                                    0
June 28      84                                    0

Because the data collected for 1992 and 1993 was not consistent in form I can not breakdown the number of colonies found per square cm. But it is important to note the changes that have occurred in their population densities over the years. To that end I put the summariares covering those years
below. I've also included notes on 1994 as this year had a period when the Carachism colonies were found in great numbers.

1992
In 1992 the colonies abruptly disappeared from the  samples on June 7. On May 31 a rock sample had its entire underside covered by colonies at a density of 40 colonies per sq.cm. On the sample taken on June 7 and those taken after this date no colonies were seen until August 2 and than they were widely scattered and rare. The colonies were occassionally found attached to free floating algae and unattached drifting alone. As stated above the colonies were able to fold up within one second and 10 seconds was the time needed to re-extend itself. The colonies were between 1 and 2 mm. high, and about the same size in
width. The Zoothamnium behaved in one way differently in May of 1992 then the colonies found in 1993/1994. These May colonies did not respond to touch by folding up. On May 10 a large field of zoos having a density of 30 stalks per sq. cm had the colonies within the field folding up apparently at random. A colony would snap shut while those all around it remained opened. This lack of response to stimuli is strikingly seen from another rock taken from a depth of 12 feet. The bottom of this rock had a Zoothamnium field with a density of 60 stalks per sq. cm. Amid the colonies were several brown hydras, one hydra moved into the dense field of zoos. There was no response by the colonies to the hydra moving among them, they did not close up when touched by the hydra, and those that were closed
opened even with the hydra right over them.

1993
          From the first sample, taken May 9, the Zoothamnium responded to touch by snapping shut. The colonies did not come close to consistently reaching the population density found in 1992. The greatest density found in 1993 was 25 colonies per sq. cm, the normal density on the rocks sampled that had Zoothamnium fields was more like between 10 and 15 colonies per sq. cm. Unlike the year before, in 1993 the colonies did not abruptly disappear, rather they slowly decreased in numbers. While decreasing in numbers though they did manage to stick around for a lot longer time, their density on June 26 was 20 colonies in a 7 cm. sq. area. The colonies disappeared from the samples after June 30.
       Carachism were more abundant in 1993 then 1992. In 1992 the Carachism were rarely found and when found the colonies were widely scattered. 1993 the Carachism colonies were not only
more common but they too were found in fields, the densest cluster seen was 13 colonies in a 1.5 cm. sq. area.

1994

The year could be considered the year of the Carachism. In 1992 and 1993 the Carachism were generally found widely scattered. In 1994 they were, for a brief period, the dominant organism on the reef. Whether this high population was due to the sampling being done earlier and the Carachism is normally
at such levels in the early Spring or some new condition in the Lake's environment caused their high density is unknown.

May 4, 2001
    This little block, making this web site more cluttered than it all ready is, covers a strange colonial protozoan known as Zoothamnium. These animals are dealt with at some length in the "Peritech" link below. Here I just want to present a photo of what a peritech colony looks like. These colonies are strange in that they seem to occur by the millions on the reef until some time in late May or early June and then they almost all disappear. The rock the protozoan colony shown in the photo below was taken from measured 11 cm. by 19 cm (a rough rectangle) and there were about 60 other colonies on this rock's underside.
    The Zoothamniums are near and dear to me because of the incredible amount of time it took to figure out what this things were. When I began this little project over ten years ago I never even heard of most of the creatures found in this report and as far as I have been able to determine Zoothamniums have never been written about in Lake Erie.
    The photo below is of a colony taken from a rock found in about seven feet of water. The colony is about 1 mm. in height and in here shown magnified at 60X.

 

            Each "bell" is a separate protozoan ( the bells can be seen more clearly in the photo below which was taken at a magnification of 250X. For a more detailed explanation of what these colonies are read the section on Peritechs.