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Update:Rotifers Avon Point(Lake Erie)
- Subject: Update:Rotifers Avon Point(Lake Erie)
- From: email@example.com (John Lavelle)
- Date: Wed, 4 Nov 1998 09:57:20 -0500
- List-Name: GLIN-Announce
- Reply-To: firstname.lastname@example.org
The following notes are basically concerned with
the Rotifers found at the reef on Avon Point in Lake
Erie. They are a continuation of the notes posted here
last month. But I always like to include notes on what
is happening on reefs bottom at the current time. This
place is so alive I sometimes think of it as a vast
cauldron of life stirred by the ladle of the winds and
it is that sense of the waters being a living thing that
I always want to impart.
Late October and November are the times when the
Lake is mine. Except for a few fishing boats several
miles out from the Point I am the only person on the
Lake or at the park. Girthing myself mentally to face
the water this time of year is always hard. Low
dark clouds and Northeastern waves make the waters
seem threatening, fear sweeps in on each cresting wave.
The rewards for continuing this research against my
own imaginary fears are great, for this is the time of
another of the Lakes seasonal changes.
The laison is disappearing, the sponges are all
degenerating and forming gemmule bodies. The hydras are
returning as in Spring (but in far fewer numbers), and
the new clusters of young Zebra mussels are establishing
themselves. The animals of the plankton are also going
through a second smaller peaking of their population
densities. This year this is especially true for the
Cladoceran, Bosmina longristris.
Below is an example of the animals inhabiting two
rocks taken in eight to ten feet of water on November 1, 1998.
The animals counted are only those .05 mm. or larger and
in general I ignore the large protozoans. Also given are
the animals found in the water surrounding the rock
and the animals in the waters at the surface.
Samples taken between 10 and 11:30 on on overcast
day. Lake water temperature is 59 F. with 2 to 3 foot
waves from the Northeast.
Rock one - size (roughly rectangular) 9 cm. by 12 cm.
Zebra mussels - 6 small (1.5 to 2 mm) scattered over
the rocks surface
2 large (15 to 17 mm.)
Hydropsyche nest 1
Byrozoan - F. sultana a small colony roughly covering a
1.5 cm diameter area.
Hydra americanus 2
Colonial hydra, Cordyphyla lacrustris - 10 hydranths, one
of the hydranths at the end of the colony is
blown up like a balloon.
Ablabsymia nests 14
Top - Laison gone from the flat area of rock (see note on
Rock two - Size (triangular) base 7 cm. height 13 cm.
Zebra mussels - 146 small (.5 to 2 mm.) found in
1 large 12 mm. long
Hydropsyche nest 1
Hydra americanus 1
Ablabsymia nests 6
Top - Laison gone but I can't tell if has been scraped off
bringing it home or has disappeared from Lake's bottom.
In summer this stuff is not scraped off and holds to
the rock's surface like glue.
Zebra mussels 3 small 1.5 to 2 mm long
Ablabsymia nests 6
Waters surrounding the above rock (5 liters)
B longristris 13
D. thomasi 1
T. mexicanus pranis 2
L. siciloides 8
E. affinis 2
Plankton 12.5 liters
L. siciloides 5
E. affinis 21
T. mexicanus 1
D. thomasi 2
Bosmina longristris 7
The following chart list the monthly average for the
total number of rotifers found in samples taken at Avon
Point. I'm presenting them but I have come to wonder
if they have any value. Unlike the crustaceans or more
precisely to a greater degree than the crustaceans, the
rotifers populations seem to achieve their population
peaks at different times of the year. Whether this is
due to temperature, food supply, or some other factor,
I have no idea. But it does seem that trying to say anything
about the rotifers as a whole may be misleading as each
species responds to the environment in different ways.
All that being said I present the data because:
1) Well I did the work so might as well present it,
2) Perhaps the data is useful and I'm just too ignorant
to see its value.
The only blanket statement I can make from the data
on the rotifers and crustaceans is the while the total
number of crustaceans seems to be going down the number
of rotifers is going up. It may be possible that there is
a direct correlation here. Some species of crustaceans
feed on the rotifers and their reduced numbers may be
responsible for the rotifer's increase. But a better study
than mine would be necessary to show this for there might
be many other causes for such population changes.
Plankton sample size 12.5 liters
In the chart below the number column is the total
number of all rotifers found in the month. The average
is the total rotifers divided by the total number of
samples taken that month. Generally there were two samples
taken every week or 8 to 9 samples a month
1994 1995 1996
number average number average number average
April 60 10 75 8.33 250 31.25
May 78 8.6 660 82.5 *1362 151.33
June 532 48.36 491 54.55 1335 148.33
July *4144 460.44 501 55.66 2787 348.37
Aug 2065 229.44 176 19.55 2697 385.28
Sept 124 15.5 379 47.38 1217 135.22
Oct 82 9.11 279 31 267 29.66
Nov. 66 7.3 102 11.33 103 12.87
Dec. 1 .12 3 0.6 10 1.11
number average number average
Jan 13 2.2 3 0.5
Feb 0 0 4 0.6
Mar 6 .7 3 0.3
Apr. 36 4 310 38.8
May 726 38 2594 324.3
June 2229 247.7 1274 141.6
July 1271 141.2 1610 178.9
Aug. 707 101 1793 224.3
Sept 1245 155.6 970 121.5
Oct. 759 84.3 925 102.8
Nov. 11 1.2
Dec. 3 .3
* The July 1994 and the May 1996 are so high because in
both these month on one date there was an enormous
number of rotifers.
July 20 1994 there were 3043 rotifers in just one 12.5
May 26 1996 there were 1073 rotifers in the sample.
To understand the dynamics of the changes in the rotifers
population densities it is necessary to look at the individual
species found. Here I'm at a big loss since I haven't the
equipment or knowledge necessary to allow me to identify
the following two groups to the species level and will have
to be content working at the genus level.
What is interesting is that the Syncheata population
rises first and then declines as the Polyarthra's
population increases. I don't know whether there is a
direct correlation such as they both occupy the same niche
and the Polyarthra is able to out compete the Syncheata or
whether there is no relation at all; that the food of the
Syncheata disappears early and the different food supply of
the Polyarthra arrives latter. It is also possible that the
different genus are sensitive to the Lakes increasing
temperature in an inverse way. There are no doubt several
other possible reasons way the one population should rise
as the other falls. Figuring out what is driving these
changes would make a fascinating study.
Below are the monthly averages using the same samples
used in the chart of the total rotifers.
1996 1997 1998 1996 1997 1998
Avg Syncheata Polyarthra
Jan 0 1.5 0.2 0 0 0
Feb 0.3 0.3 0 0 0 0
Mar 11.7 0.2 0.1 0 0.3 0.1
Apr 5.8 2.3 32.1 0.1 0.4 0.8
May 144.3 86 283.1 17.4 0.3 17.5
Jun 64.4 160.7 0.2 42.1 56.9 135.7
July 61.1 34.9 5.6 274.6 98.7 135.8
Aug 10 4 53.9 301.3 80.3 145.3
Sept 23.8 20.9 7.3 72.3 100.6 101.4
DIFFERENCES IS SURFACE AND BOTTOM SAMPLES
There are many sampling dates when significant differences
are found between the surface samples and the benthic samples.
Problem is what is a significant enough difference to allow
me to say that the animals are actually at different levels
in the water column or the differences are sampling errors.
Here I am assigning significance only to those dates that
have a ratio of more then 2 to 1.
Under the second column, rotifers, are the number of
animals found in a 5 liter sample. Under the column X-2.5
are the number of rotifers in the sample times 2.5 to
have that sample equal the plankton sample of 12.5 liters.
The last column, Plankton, is the number of rotifers in
the 12.5 liter sample. The bottom and surface samples
were taken about one-half hour apart.
The numbers for these dates in 1996 were:
Benthic Rotifers X-2.5 Plankton
6/2 8 20 110
6/9 2 5 15
6/30 135 337.5 726
7/27 45 112.5 302
8/18 235 587.5 167
9/1 166 415 43
9/5 66 165 485
10/6 3 7.5 19
10/16 25 62.5 13
Bear in mind that these samples were all taken in
the morning so vertical migration due to
light does not appear to be a reason for the animals
distribution. Though in the case of these animals
wave currents alone may account for the animals
distribution. But even if the animals are distributed
by currents these wide variations present real
problems in coming to terms with the animals
Again, as in the last set of notes I posted I
want to stress my disdain for the use of "patchiness"
to explain the uneven distribution of animals in
the waters of the Lake. Whether rotifers are members
of the plankton (using the strict definition of "plankton")
may be a function of wave length. On days of calm
these animals may, like the crustaceans, be animals
of the nekton.
I have always been torn between two wishes as this
study has been done over the years. One, that out on the
Great Lakes there is someone well ahead of me who
understands why all the things that I observe are occurring
on the Lake and that they will come over the horizion spreading
light on all the dark mysteries I keep encountering. The
second wish is that no one is working on this kind of
project at all nor has anyone any intention of doing
so. This wish allows me the joy of making discovery after
discovery. I know in this day of specialization that the
works of an amateur is never going to be taken seriously
by the scientific community but I can't help feeling a
bit like Darwin or more exactly Wallace, faced with a mountain
of new data coming from an unexplored world, wrestling alone
with the unknown, and having the spectacular grandeur of life
on earth paraded through the years before my eyes.