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Update:Rotifers Avon Point(Lake Erie)





    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.
Bottom
   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 below)
Rock two - Size (triangular) base 7 cm. height 13 cm.
Bottom
   Zebra mussels  -  146 small (.5 to 2 mm.) found in 
                         two clusters
                       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)
  Crustaceans
   B longristris          13
   D. thomasi             1
   T. mexicanus pranis    2
   Harpactacoids          7
   L. siciloides          8
   E. affinis             2

  Insects
   Stenonema              2
   Ablabesmyia            7
  
  Annelid                 1

  Nematodes               10

  Rotifers
   Unidentified           1
   Polyarthra             5
   Syncheata              1

Plankton    12.5 liters
  Crustaceans
   L. siciloides          5
   E. affinis             21
   T. mexicanus           1
   D. thomasi             2
   Nauplii                2
   Bosmina longristris    7

  Rotifers
   Polyarthra             6
   Unidentified           1


                         ROTIFERS
     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

            1997             1998
      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 
liter sample.
  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
                     OF ROTIFERS
     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
6/12                            23
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 
density.
    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.

==========================================================
                Afterword

    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.
                          John Lavelle