In terms of benthic studies and photography this year has been the worse in the last five or six years. The area has had much need steady rain over the spring and summer and the wave action has been detrimental to my getting down to the bottom of the reef very often. Perhaps too my getting older has something to do with it. When I first began this study four or five foot waves would not detered me from going out and getting samples. I enjoyed riding the surf and getting pounded by waves as I both swam out and tried to come back.
ROUNDED GOBIES
They are still with us in what looks like a population density that is unchanged from what it has been the last several years. This doesn't surprise me. I had thought that the population would have collapse by now, but whenever I think something is going to happen I'm usually wrong. They're still down there doing their utmost to get into every picture I take. I still haven't figured out what their eating. The Zebra mussels are still found in what looks like the same density as they have been over the years.
So many of the animals that were once present
in large numbers have are still locally extinct. The several species of
caddis flies (Trichoptera), all five species of snails, the planarians,
while not extinct, are not the same species that was here before and the
ones that are found are very rare.
Below is a red colored planarian, one of the few planarians of any type
seen.
And while so many animals have disappeared the bryozoans seem to still be benefiting from their being gone. Two insects that one would think of as prime gobiy food, the midge larva, Ablabesymia and the mayfly larva, Stenonema, both seem to have maintained the same population density. How much the gobies are responsible for the changes in the make up of the biological communty I can't say, nevertheless this ain't the same Lake that I studied before they came.
ZEBRA MUSSELS
In 1999 I saw no signs of
spawning taking place. Till that year every fall small Zebra mussels would
be found on the bottom of rocks. This year ( 2000) the mussels began spawning
again. At first I thought the gobies were eating the young mussels which
is why they didn't appear in the samples in 19990 but this must have been
wrong and some other factor must have been in play in 1999 because the
2000 spawning was as evident as in other years before the coming of the
gobies. To give an example of the spawning numbers I give the data from
the first sample on which the young mussels were found.
September 2nd, 2000 - the rock is triangular
in shape measuring 9 cm. x 12 cm. x 11 cm.
Zebra mussels 126
They are found in three sizes rangeing from .5mm. to 2mm.
Ablabsymia nests 30
Bryozoan colonies- F. sultana I can't tell if there
is 1 or two colonies present.
The young mussel were found on all the samples taken after this date.
Below a photo of a zebra mussel covered rock in the fall of 2000.
I want to stress what I stated in the introduction about 90% of the reef is completely free of zebra mussels and looks likes the photo below.
(There are two sponges on the upper rock on the right and side. The sponge
in the foreground is breaking up into gemmule bodies.)
SPONGES
The photos below of the two sponges
were taken in the fall when the sponges were going into gemmule formation,
regretfully the Lake waters were so full of suspended particles that I
have no good photos of sponges in their mature state. It was I think a
good year though for sponge growth, but it would be impossible for me to
quantify their density in comparison with other years. The two photos give
a good view of the struggle between the laison and the sponges. If you
look closely at the edges where the sponge meets the laison you can almost
feel the tension between the two life forms competing for space.
BENTHIC SAMPLES
I am truly embaressed by the paltry number of samples taken this year. There are so few that I can present all of them below. Which such a small number it would be foolish to try to draw any meaningful conclusions about changes in the benthos compared to prior years. But I will make a few comments on what might have been changes in comparison to 1999.
HYDRAS AND PERITECHS
My reason for combining these two radically
different groups of animals are that they both are found in the same place
and occur in their greatest numbers at the same time of year.
The number of hydras increased in the few samples taken with the greatest
amount being found on a rock sampled on July 9. This is unusual as the
hydras in prior years usually disappear from the samples in summer. Their
numbers seem to be greater than in 1999.
The zoothamniums have a loww population
density as compared to the years when I first started studying the reef
but this low density may be only a reflection of the fact I started the
sampling in late spring.
All the animals
listed below were found on the rock's underside.
May 17th, 2000
Second rock
sample. Rock size 6cm. X 12cm. from a depth of 8 feet.
Hydra americanus 8
Zoothamnium
4
First rock sample
Rock size roughly about 35 sq. cm
Hydra americanus 1
BRYOZOANS
The Bryozoan Fredericella
sultana was as abundant as it has been over the last three years.
June 10th.
Rock size 10cm.
X 15 cm.
3 Byrozoan colonies, Fredericella.sultana. Two of them cover roughly
2cm. sq. the other is about 1cm. sq.
Colonial hydra, Cordaphyla lacrustris, colony covers an area about 1.5cm.sq
Hydra americanus 3
Ablabesymia nests 2
Planarian (photo in introductory page)
1
Zebra mussels 1
(10mm. long)
June 14,
Rock size, very roughly,
about 100 sq. cm.
Hydra americanus 27
Planarians (not Dugesia) 2
Zebra mussels
2 (10 to 12 mm. long)
July 2
Rock size, 4 cm. 15
cm.
Hydra americanus 19
Zoothamnium
7
Rock 2 7cm.X
7 cm.
Hydra americanus 22
In the water that surrounded these rocks were found
Hydra americanus 17
Mayfly (Stenonema) 3
Body size 1mm. tail size 1mm.
July 6
Rock size about 45 sq. cm.
Hydras
55
Zoothamnium
2
Ablabesymia nest (midges) 7
In the water surrounding there were found
Hydras
2
Harpactacoids
12
Mayflies
8
Midges
5
July 9
Rock size about 64 sq. cm.
Hydras
9
Bryozoans F. sultana
3 colonies
Zebra mussels
16
(2 small 1 to 2 mm. 14 large 8 to 12 mm.
Midge nests
4
In water around rock
Mayflies
6
Harpactacoids 5
Midges
2
Sept 2
Rock size 54 Sq. cm.
Zebra mussels (spawning has taken place)
126
three sizes from .5mm. to 2mm.
midge nests
30
Bryozoan colony
1 or 2 couldn't tell
if these two colonies were connected
Sept 10
Rock size 180 sq. cm.
Zebra mussels large 10 to 20
mm.
7
small .5 to 1.5 mm.
60
Midge nests
12
Hydra a new species see photo
in introductory section
Sept 20
Rock size 96 sq. cm.
Zebra mussels large 8 to 20 mm.
15
small <1 mm. to 2 m.
192
midge nests
3
Bryozoan colony covers roughly
a 9 cm. sq. area
Sponges seen on dive, they were abundant,
still green in color, and none of them had gone into gemmule body formation.
Oct 11
Rock size 90 cm.sq.
Zebra mussels 4 to 6 mm.
5
.5 to 2 mm
97
Zoothamniums
4
Hydra americanus
1
Midge nests
8
Bryozoan colonies
3 "tentacles" visible
in only one colony F. sultana
Nov 1
Rock size
54 sq. cm.
The red planarian (see above photo)
Zebra mussels .5
to 1 mm.
15
Zoothamniums
5
midge nests
8
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