[Date Prev][Date Next][Date Index]
Lake Erie, Central Basin Research Update
- Subject: Lake Erie, Central Basin Research Update
- From: firstname.lastname@example.org (John Lavelle)
- Date: Wed, 30 Sep 1998 12:32:11 -0400
- List-Name: GLIN-Announce
- Reply-To: email@example.com
The following is a summary of research being down on
a hard benthic area of Lake Erie's Central Basin and
a study of the zooplankton.
THE SHALE REEF AT AVON POINT
A brief overview of the change taking
place in 1998.
...like a dog walking on his hinder legs.
It is not done well; but you are
surprised to find it done at all.
For the vast majority of people who are not
acquainted with my biological work in Lake Erie let
me introduce myself by saying I am an amateur naturalist
who works with the most primitive of equipment. I think
of myself as being more closely fitting into the
atmosphere of the late 18th century than with the
current researchers, with whom I have almost no contact.
Though there are are two important exceptions to the feeling
of belonging to 18th century, one is this work is being done
on a personal computer, the other is to have
the works of G. Evelyn Hutchinson "A Treatise on Limnology"
to use as my primary reference.
Throughout the ten or so years I have been working
on this project I have been faced with an ecosytem that
has been subject to vast changes. Every time I think I
have achieved a rudimentary understanding of what is
going on on the reef the whole ecosystem seems to go
through a vast convulsion leaving me with new dynamics
to understand and leaving my earlier works useful only
as comparisons to the changes taking place.
I study a small shale reef in Lake Erie, found off
an area known as Avon Point, which lies about half way
between the cities of Lorain and Cleveland, Ohio. This
area of the Lake rest on a small shelf on the rim of
the Central Basin of Lake Erie. The water's depth quickly
drops to 10 to 15 feet and remains at that depth for about a
mile out. The reef was formed by the collapse of
the shale cliff walls that form the shoreline and are
the bedrock of the area. Overlaying this shale is an enormous
amount of glacial till. Under the shale and stretching
out beyond it is a bottom of blue clay. There is very little
sand or mud because this area is unprotected from the large
waves generated by one of the longest fetches on Lake Erie
and the area, because of the peninsula created by Avon Point,
is subject of a littoral drift the runs against the
prevailing Lake current. Whereas Lake Erie's water generally
flows from West to East, at Avon Point the near shore water
flows from East to West. These combined currents tend to
remove all loose sediment from the bottom area. There is a
stream that empties into the reef area. Though the stream's
mouth is slightly to the West of the reef because of the
ancient stream bed that lies underwater the streams runoff
is turned eastward and runs over the reef.
There is a basic reoccuring cycle on the reef. The
cycle is not constant but the following gives an idea of
the dynamics of life even though the population density
and timing of when animals appear fluctuates from year
In the Spring the rocks are dominated by the colonial
peritechs; Zoothamniums and Carchesiums. To give an indication
of the number of colonies found on a typical rock let me give
two examples. May 18th 1997: a rock 13 cm. by 12 cm. and 1 cm.
thick on its top and sides had 80 Carchesium colonies and
6 Zoothamnium colonies. On the rock's bottom there were
23 Carchesium colonies and 149 Zoothamnium colonies. There was
no laison and only one Zebra mussel on the rock. The number
of peritechs is highly varible on the rocks from none to 891
on a triangular clay block having 2 sides 12 cm long and a
base 13 cm. long and 3 cm. thick. In years past the peritechs
would disappear by the middle of June but this year, 1998,
they have stuck in reduced numbers right up until the
present (Sept. 1998).
A final note on these colonies. Zoothamniums are normally
known to be epibonts, this is the first time that the have
been known to live in vast number on inanimate objects.
Begining in late May and early June the Hydras take
over as one of the dominant life forms on the bottom
(see chart below).
By mid June the laison is growing strong and continues
to hold on the upper surfaces of the rocks right into
By Late June the Hydras have either disappeared or are
waning in numbers and the insects Ablabsymia and Hydropschye
as well as sponges and up until 1996 Planarians are all
increasing in numbers
For the first eight years of this study the Bryozoans
were extremely rare on the reef. Beginning in 1997 the species
F. sultana has become one of the most common animals found.
They are found on about half of all the rocks sampled
in late Summer. This increase in colonies is continuing
In the Fall the Colonial Hydra Cordylophora
lacrustis (or Cordylophora caspia) make their appearance.
The sponges start forming gemmule bodies and the laison
disappears. The ostracods and amphipods begin increasing
Regretfully, since I lack a dry suit I haven't been
able to explore the reef in winter.
With the above extremely incomplete introduction,
I would like to present a look at what is happenning on the
reef and the waters above it in summary form up to and
including September 1998. This is by no means a complete
report it will take me several months (or longer) to put
all the data in some kind of format and the project is
an on going one so it is constantly being revised.
IN THE FOLLOWING DATA IT MUST BE UNDERSTOOD THAT I AM
NOT SAYING THAT THE POPULATION DENSITY FOR THE LAKE AS A
WHOLE OR EVEN THE CENTRAL BASIN IS REFLECTED IN THE NUMBERS
PRESENTED HERE. THE CRUSTACEANS (AND PROBABLY THE ROTIFERS)
ARE MEMBERS OF THE PLANKTON OR THE NEKTON DEPENDING ON
WAVE LENGTH AND/OR SEICHE (AND POSSIBLY OTHER FACTORS SUCH
AS MATING AND FEEDING). THEREFORE DETERMINING WHETHER THE
POPULATION DENSITIES OF THE CRUSTACEANS ARE DECREASING OR
INCREASING CANNOT IN ANY ABSOLUTE SENSE BE DETERMINED FROM
ANY OF THE FOLLOWING FIGURES. THE NUMBERS ONLY SHOW A
RELATIVE CHANGE OF THE NUMBER OF ANIMALS FOUND IN THIS
PARTICULAR AREA OF THE LAKE UNDER NUMEROUS CONDITIONS.
I FIRMLY BELEIVE FROM THE DATA GATHERED THAT THE DYNAMICS OF
THE ZOOPLANKTON IS FAR MORE COMPLEX THAN IS GENERALLY
BELEIVED (AND I AM NOT TALKING ABOUT THE CATCHALL "PATCHINESS"
SOME PEOPLE ATTEMPT TO EXPLAIN VARIATIONS IN THE ZOOPLANKTON).
Before listing the data on the copepods found in the
waters above the reef I would like to give an example to
those unfamiliar with the great number of animals found in
the waters of the Lake a glimpse of rich in life the
Lake can hold. The following example is old and, as will
be seen by studying the tables below, the number of
crustaceans has decreased significantly since this data
was collected. It still give a picture of the enormous
amount of life in the waters. After working with these
numbers I actually starting feeling guilty every time I
took a shower or flushed the toilet realizing the numbers
of animals that died providing my creature comfort.
The data is taken from 1995 using the 12.5 liter plankton
samples and the 5 liter benthic samples and projecting them
into a 1 cubic meter area.
June Plankton Benthic
Cyclopoids 13104 1012.4
Calanoids 4079.5 555
Nauplius 9319.68 907.4
Bosmina 7447.68 698.4
July Plankton Benthic
Cyclopoids 1470.96 445.6
Calanoids 175.68 45.6
Nauplius 2119.68 391.4
Bosmina 820.8 77.4
Monthly Averages for Copepods
The following data is based on 12.5 liter samples taken twice
a week. All the samples where taken in the morning from the
Calanoid Copepods 1993 to 1997
1993 1994 1995 1996 1997 1998
Mar. 2.2 2.6 .9 1.56
Apr. 7.7 3.7 3.5 4.5 24.1
May 104.3 84.8 37 40.5 11.6
June 12.75 71.4 56.7 60.7 *144 27.8
July 4.85 22.4 2.4 28.4 8.5 4.6
Aug 4 16.7 5 28.1 7.1 2.6
Sept 26.57 32.1 13.6 6.8 11 12
Oct 15.55 11 9.3 34.6 6.3
Nov 9.11 9.9 5.3 2.9 4.9
Dec 5.57 6.3 7.2 5.6 .8
Average of the 31.3 20.9 23.04 25.3
Calanoids Apr. thru Dec.
1994 to 1997
* 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 nonrandomness 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
The cyclopoid copepods had a sharp drop in the numbers
found in the samples. 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 found it could be found in large numbers.
Comparison of Cyclopoids Copepods from 1993 to 1997
1993 1994 1995 1996 1997 1998
April 8.6 9.77 3 .3 2.1
May 38.33 56.75 50.33 8.9 34.7
June 51.5 38.77 182 109.36 35.4 59.1
July 25 26.6 19.55 17.13 30.2 6.3
Aug. 38.5 13.7 19.11 5 7.7 3.7
Sept. 17.28 12.5 7.12 17.33 2.9 1.2
Oct. 8.55 13.1 3.77 8.88 2.3
Nov. 12.88 7.7 5.66 1.5 4.3
Dec. 10.71 5.13 4.4 7.66 1.1
Average for the 18.277 34.23 24.46 10.3
years 1994 to 1997
Apr. to Dec.
No attempted was made to distinquish between cyclopoid and
1993 1994 1995 1996 1997 1998
Jan. 3.25 3.8 0.3
Feb. .75 1.9 1.4
Mar. 9.5 1.4 .9
Apr. 36.16 28 8.25 61.3 33.4
May 133.97 161.25 63.55 13.8 53.4
June 13 61.3 129.44 121.22 64.8 38.5
July 2.71 27.66 29.4 51 48.6 5.2
Aug. 4.5 49.55 70.44 30 15 9.8
Sept. 6.57 26 40.12 49.66 10 38.4
Oct. 4.77 10.22 13.11 44 8.8
Nov. 6.44 2.88 4.44 1.625 2.8
Dec. 4.57 5.62 2.4 1.66 .2
Yearly average 39.26 53.17 41.21 25.03
from Apr to Dec.
I am leaving out the data on Cladocerans because monthly
averages is misleading in their case and listing
every date would make this brief report far longer than is
intended here. Why I think monthly averages for these animals
is misleading can be seen from dates given below.
August 27, 1995. The time, 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
Daphnia retrocurva 340
Leptodiaptomus siciloides 20
L. kindtii 14
Tropocyclops mexicanus 123
Diacyclops thomasi 75
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
Aug. 26, 1995
12.5 liter sample
T. mexicanus 308
D. thomasi 3
Below for the purpose of comparison is the count of the sample
taken on July 13, 1994. While there are differences in both the
number of animals found and the species making up the sample what is
striking is the simularities between the 2 samples. What is
especially noteworthy is the presence of so many L. kindtii in
the sample. These large zooplanktoners are never present in this
large of a number in any of the regular 12.5 liter plankton
samples. (these notes where written in 1994, this year,1998
I've found in on sample taken on Sept. 13 - L. kindtii- 33.
Strange that this Sept. 13 sample also had an extraordinarily
high number of T. Mexicanus pranis - 93.
July 13, 1994
5 liter sample
Daphnia retrocurva 674 1 to 3 mm in length
L. kindtii 5 4 mm.
D. thomasi 63 .75 to 1.5 mm.
L.siciloides 3 1.25 to 1.5 mm.
Nauplii 16 .10 to .25 mm.
Diaphanosoma 3 1 to 1.5 mm.
Bosmina 5 .5mm
July 13, 1994 Plankton sample 12.5 liters.
A regular 12.5 liter plankton sample taken within 1/2 hour of
the 5 liter sample shown above had a count of:
Cyclopoid copepods 15
Throughout this study I have found that frequently the
Cladocerans seem to move in clouds.
Writing these brief notes I realize how terrible far behind
I am in bringing the data together. The numbers haven't been
worked out for this important group of animals for 1997 and
They have maintained their population density of about 10
per square meter, a level they reached in 1997.
The genus Stenonema has had probably the biggest change in
it population density in 1998 than any other creature on the reef.
Taking as an example of 5 rocks sampled on three different dates
in August (the mayfly population surge began in August), the
rocks had a density of 0.1 per square cm. as opposed to 0.01
per sq cm. in 1997 in sample taken during the same time period
The five species (except for the genus Ferrissa) that use to
inhabit the reef in great numbers continue to be totally absent
from the area. Two snails of the genus Ferrissa were the only
snails seen this entire summer.
The Triclads of a genus of Dugesia for the first 8 years of
this study were very abundant.
# per cm.2 # per sq. meter
1994 1995 1996 1994 1995 1996
May 0.002 0.021 0 22 214 0
June 0.022 0.028 0.003 221 287 30
July 0.031 0.035 0.026 318 352 260
Aug 0.053 0.063 0.039 539 635 390
Sept 0.068 0.041 0.042 681 413 420
Oct 0.066 0.038 0.02 664 387 200
I believe the number of planarians per square meter is
probably closer to 1/2 the number found in following table.
I say this because probably only a very few areas on the
reef provide suitable habitat over an entire square meter.
In 1997 these animals all but totally disappeared, only
several were seen the entire year. In 1998 this disappearence
has continued, only 2 have been seen the entire summer.
Average monthly population density for hydras.
The numbers are the average number of hydras per square cm.
The rock surface area is only the area of the rocks underside.
1993 1994 1995 1996
May 0.078 0.0007 0.0016
June 0.203 0.2318 0.4069 0.1344
July 0.281 0.1123 0.1393 0.093
Aug * 0 0.0091 0.007
Sept * 0.0016 0.0476 0.014
Oct 0.383 0.0034 0.0254 0.012
I haven't worked out the numbers but in both 1997 and
1998 the number of hydras seems to have been decreasing.
Again I'm way way behind.
Cordylophora lacrustis (or Cordylophora caspia)
The opposite of the decreasing numbers for Hydras has
occurred for C. lacrustris. Their numbers this Fall have
increased. There colonies have been found on between a
quarter and half of all the rocks sampled. It has always
been an interesting point that these colonial hydras only
make their appearance in beginning in late July, they are
never found in Spring or early Summer. Also Hutchinson wrote
that in these colonies the hydranth are always found
horiziontally or obliquely to the bottom, this is untrue.
On this reef the animals are almost found with the hydranth
facing vertically down
Since the collapse of the Zebra mussel population in
the winter of 1991-1992 the mussels have maintained a
rather steady state. Each August and September there is
a large spawnING of the mussels and each winter almost all
of the young and many of the older mussels are torn from
the rocks and washed up onto the beach. This area takes
a tremendous pounding in Winter from the Northeast winds
that seems to rip these mussels right off the rocks or the
rocks themselves smash into each other killing the mussels
living on them. Most upper surfaces of rocks have no mussels
on them at all. Generally it is only the large round boulders
that are mussel encrusted. A ballpark figure would be that
80% of the rocks have no mussels at all on the upper surfaces.
I can see no evidence that the rounded gobies are
eating the mussels, even with the great number of gobies
present in the area there has been no decrease in the
number of mussels. For the life of me I can't figure out
what the gobies are eating.
This is only briefest of overviews of what is occurring
on the reef. I have left out the data on: Sponges, Ablabesmyia,
Hydropshche, Harpactacoids, Amphipods and many of the lesser
players in the ecosystem. Anyone wanting data on these animals
are encouraged to write.
Much of the older data for the years 1994 and 1995 is
available in the Science section of the Lorain County Freenet
which can be reached at:
I've seen them set to dance
by waves dragging up the sands,
tossed with directed fury
by meaningless winds of chance.
Rushed to hopeless flight.
Swirling towards death in light.
Claws ripping through water
The Naiads blind to their plight.
Oct 28. 1997