O
Microscopic Algal Food of Littorina planaxis and
Littorina scutulata
Michael S. Fostel
Biology 175h
May 30, 1964
Dr. Blinks
Microscopic Algal Food of Littorina planaxis and
Littorina scutulata
Littorina planaxis and Littorina scutulata are commonly
observed inhabiting the granitic upper littoral and supra-
ittoral areas generally devoid of macroscopic algae. This
tudy was undertaken to determine what microscopic algal type
the animals were feeding on in these seemingly bare areas and
get an idea of the effects of this feeding on algal growth.
The study is conveniently divided into two parts: 1. Iden-
ification 2. Determination of standing crop of microscopic
lgae and the effect of littorines grazing upon it.
Identification
Methods
Rock specimens were removed from areas inhabited by the
littorines in the 6 to 8 foot range above mean zero tide.
Their surfaces, crevices, and cracks were scraped into ster-
ile sea water and then plated on an agar culture medium.
The mediums used were of two basic types. Medium 1 was
made up of 2% agar in sterile sea water plus 10-3molar Na,HPo
and 10 3molar NH,NOg. A soil extract was prepared by mixing
crushed granite with dark soil in 1 to l proportions; To this
mixture was added 2 parts sea water and the soil-granite and
vater were heated at 90°C for one hour. The mixture was then
filtered and the brownish liquid filtrate was added to the
culture medium, 1 part soil extract to 10 parts agar plus sea
Pringsheim, 1946.
e
aic
C
ater.
Medium 2 was identical with medium 1 except NH,NOg was
omitted and 10  molar NaMo0, added. This medium was used
to encourage the growth of possible nitrogen fixing blue-
green algae present.
In addition to the above mediums, two more were made,
one using medium 1 with a salt concentration in the sea water
four times normal (4X sea water), and another using medium 1
with L. planaxis mucus and feces spread over the surface.
Both were prepared to approximate more closly the natural
habitat of the algae.
Many snail shells, especially those of L. planaxis, have
very green color and are deeply eroded and pitted, and snails
are normally observed crawling on one another. It was thought
that the green may be a source of microscopic algal food,
and perhaps the cause of the erosion. Therefore, the outer
surface of a green shell and a brown eroded shell were scraped
and plated on medium 1.
Snails of both species were collected after high high water
le moving, dissected, and the stomach contents plated on
poth mediums 1 and 2 to culture any undigested pieces of algae.
Lastly, since the littorines åre splashed regularly during
igh tides, some sea foam was collected and plated to identif.
possible algal food sourees not livingidirectly in or on the
granite rocks.
The cultures were placed upside down in front of a north
window which had been covered with tissue paper to prevent
116
leaching frou dirset suhlight.
In addition to culturing, rock Specimens, shells, and
tomach contents were examined directly in the laboratory.
Results
he results of both eultures and field observations are
presented in the chart on page 12.
The first growth in culture consisted of bacteria, but
fter ten days a conspicious growth of diatoms appeared,
specially from rock surface scrapings on medium 1. After 15
s most of the algae to be described began to grow, and 2
were subcultured.
The alga giving the common green coloration to round
ocks in tide pools and to granite surfaces above tide pools
was identified as the chlorophyta, Spongomorpha coalita (see
Plate 1, fig. 1). This form has the general appearance of
(744
he description given by Smith but is a much smaller, juvenile
State. It was found much higher than the description by Smith,
rowing well within the littorine range at 6 to 8 feet. in
mall cracks in the rock surface and on the surface itself.
was also grown from stomach contents and in sea foam
ulture. The growth in sea foam was probably from pieces hg
11. 6.1
washed from the rocks.
The green alga growing in the outer layers of the shells
L. planaxis was identified as Entocladia testarum (Plate
fig. 2). Previously, this alga had been described in the
2. Smith, 1944.

3. Thivy, 1943.
pvne
United States on the east coast only,)nhabiting dead molluse
shells.4 Growth was also found in stomach contents of both
species. When the outer layers of eroded shells were dissolved
with HGl and the underlying material scraped off and examined,
the alga was very prevelent, especially the massive, spherical
thallus of overlapping, fused filaments. Since E. testarum
grew well from scrapings of a brown eroded shell with no visible
surface green, it may be the agent responsible for the shel.
erosion.
a3
Prominent among the blue-greeny found were Plectonema
terebrans (Plate 1, fig. 3), Calothrix pilosa (Plate 2, fig. 4),
and Calothrix crustacea (Plate 2, fig. 5). These algae fit the
(146)
general description given by Umezaki.k Plectonema terebrans
ffers from Umezaki's description, being found here in shells
of live L. planaxis and on the granite rocks in close ass-
ociation with the other blue-greens and with S. coalita pre-
viously mentioned.. It could also be responsible for some of
the erosion of shells, since it is a shell boring form. All
three of these blue-greens were found in cultured stomach
contents and P. terebrans was found in sea foam (probably
washed from rocks). C. pilosa was very abundant in the stomach
planaxis. Generally, the blue-greens did as well in
medium 1 as medium 2 so the presence of nitrogen fixing forms
doubtful. bessite
4. Thivy, 1943.
5. Umezaki, 1961.
anttos

mele
Dermocarpa sp. (Plate 2, fig. 6)8 and öpiruliha sp.
(Plate 3, fig. 9)7, two other blue-greens, were found in lim-
ited quantities. The Spirulina was found in association with Pcko
P. terabrans on rock surfaces, and Dermocarpa was found grow-
ing on Rhodochorton Rothii filaments in the field only.
Roodochorton Rothii was the only red found, commonly in
crevices receiving very little sunlight. L. planaxis is often
observed in these crevices and some pieces of R. Rothii were
found in their stomach contents, although none grew in culture.
This species fits Smith's description except for its growing

0.
in crevices.
lje
Diatoms and unicellular greeng and blue-green, were found
most cultures but no attempt was made to identify them.
The diatoms were especially abundant both in rock cultures and
stomach contents, and seem to constitute one of the primary
food sourees of the littorines.
Determination of Standing Crop and Littorina Grazing Effects
Methods
Chlorophyll content
In an effort to determine the standing crop of all the
microscopic algae in the 6' to 8' range, areas of rock were
chipped from the surface with hammer and chisel. The chloro-
phyll and other pigments were extracted with methyl alcohol and
their absorbtion spectra determined. The rock spectras were
6. Smith, 1950.
Gk
130
y, +
8. Smith, 1944.
9. Castenholz, 1961.
C
compared with the absorbtion spectrum of a similar sige
piece of Ulva.
The rock samples extracted were 5 cm by 5 cm square and from
to 10 mm deep, depending on the depth of the green color-
tion beneath the surface. Because this depth varied, all
calculations were based on surface area and not volume.
The rock samples were crushed with a mortar and pestle,
laced in dark screw cap bottles, and covered with 50 ml ab-
jolute methyl alcohol per 25 cm2 rock. Acetone and ethyl
alcohol were tried but did not affect complete extraction.
The bottles were then placed in a refrigerator for 29 hours,
ontents filtered through l filter paper, and immediately
analyzed on a Beckman Modal DUR spectrophotometer at wavelenghts
from 430 to 680 millimicrons.
Samples of Ulva were cut into 1 cm squares and extracted
ia similar manner without grinding. The absorbtion values
nsis histt
were
corrected to 25 cm2 Ulva/50 ml alcohol.
To get an idea oflthe algal content of the L. planaxis
estimale
alls, spails were removed and their shells crushed and
extracted as above. The absorbtion spectrum was corrected
to 25 cm shell sufface/50 ml alcohol. The shell surface
estimations are described under Photosynthetic Rate.
b. Photosynthetic Rate
Rock samples were removed intact from outcroppings and
a 25 cm surface area exposed, the rest of the rock covered
ith aluminum foil to prevent light from entering. The rocks
were placed in one liter jars filled with sea water of a known

120
og concentration, and placed in the sun for 2 hour.
The
rocks were then removed and the water ånalyzed by the Winkler
method to determine Og increase. From this, carbon productior
s calculated.
Ulva's photosynthetig rate was previously determined (see
under Final Determination of Standing Crop).
The photosynthetic rate of snail shells (L. planaxis) was
determined by cracking the shells to remove the snails and
putting the shells in sea water in direct sunlight. 02 in-
crease was again measured by the Winkler method. Snail sur-
face area was calculated by approximating with 1/ of wr/r24 h2
the formula for the area of a right circular cone. R here is
the distance across the operculer opening and h the height of
the shell from the bottom of the operculer opening to the to
the spire.
Respiration Rate
Only the respiration rate for a 25 cm granite surface
measured. This was done by chipping a rock to the de-
sired dimensions and putting it in sea water in the dark for
12 hours. Op concentration before and after was measured
the Winkler method and Og decrease calculated.
Results

Chlorophyll Content
The absorption spectra of an adverage of three 25 cm2
ock surfaces, three l ome pieces of Ulva corrected to 25
eme, and four crushed shells with a surface area of 6 cme
corrected to 25 cm2 are presented in the graph on page 13.
ke
10. North, 1984.
C
since chlorophyllta)is present in all the algae found, this
jas used as a standard of comparison.
Using Strickland and Parsons! method, chlorophyll ta) con-
nt was determined by the formula
Ca - 15.6 Eggg - 2.0 Eg4g - 0.8 Eg3o
- mg chlorophyll a)/ liter of solvent
(when absorbtion is measured in a lom
cell) and Ersees
Values obtained were corrected to one liter of methyl
alcohol and then to one meter squared of rock surface.
Granite surface in 6-8 ft. tidal level
adverage of three samples
.043 gs chlorophyll e)/ m
nis value is probably(gomewhat less than the exact(value
because of the presence of blue-green (pigments) abga
Ulva chlorophyll (a) content using the same formula:
Ulva (adv. of 3 samples) - .081 gs Ca / me
Shell ohlorophyll k)content was not calculated because
after 29 hours the shells were not completely extracted. It
is significant that even with incomplete extraction the shells
have a higher pigment content than either the Ulva or the rock.
see graph, page 13)
Photosynthetic Rate
Rock surface (adv. of 4 samples):
- 7.8 m1 0,/25 cm2/ day
- 3120 ml 02/ m2/ day (assuming 12 hours o.
light)
1960.
Parsons,
11. Strickland and
* E is extinction or absorbtion.
/22
1.6 ga carbon/n/ day
Ulva previõusly determined for Hopkins Marine Station:
- 3 - 7.2 gs cärbon/m2/day
Shells (L. planaxis adv. of 4 samples):
- .981 gs carbon/m/day
Respiration Rate
Rock surface (adv. of 3 samples):
246.8 ml 02/m2/day
Final Determination of Standing Crop
ince the photosynthetic rate of the granite surface
turns out to be about half that of Ulva's minimum value,
and the chlorophyll (a)content of the granite surface is approx-
imately half that of an equal surface of Ulva, then it is
assumed that chlorophyll a content and standing crop are re-
lated and that the relation for Ulva is proportional to that
of the algae in the granite surfaces. If this assumption can
be made then dividing Ulva's Ca content into that of the rock:
.043 -r.081 - .53
Standing crop of Ulva for Hopkins Marine Station
- 70 gs carbon/m?
Then the standing crop of algae on the granite
surfaces
- (70) (.53) - 37 gs carbon/m2
Dividing standing crop by production rate we
get time for crop on rock
- 37441.66 = 22.3 days
chart summarizing the results of standing crop deter-
minations is presented on page 14.
130
C
Effects of Grazing
Methods
For this determination a flat surface was selected at the
tide level. Six baskets of 15 cm by 15 cm by 5 cm size
were fastened to the rock by bolts driven into the granite.
The area received abundant splash and spray during high tides
and was inhabited by littorines of both species, but prim-
arily L. planaxis.
Ten snails (L. planaxis) with a volume of .27 co/snail

were introduced into each of three of the baskets while
the other three baskets were kept empty.
After 25 days the baskets and snails were removed and
emf sections of granite were chipped from the center of
each basket-covered area. The rocks were analyzed as in
previous chlorophyll(a) determinations to ascertain any dif-
ferences in pigment content which could be used as a measure
of food consumed.

Results
The absorbtion spectra of the grazed and ungrazed surfaces oo

are presented in the graph on page 15. Chlorophyll a content
was not known before the test,so its calculation would not
be meaningful.
For a general measure, subtracting the absorption values for
grazed and ungrazed surfaces at the peaks gives a value of
from 66 to 104. Therefore, 10 snails with a volume of 2.7 cc
grazing on a 225 cme surface of granite reduce the pigment
content by about 8% when compared with an ungrazed surface
nterd durtes
over a period of 25 days.
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Summary
lene
Algae identified in the habitat of Littorina planaxis and
Littorina scutulata- (7 denotes positive identification as
food)
Chlorophyta
alita
Spongomorpha
Entocladia testarums (on shells)
greens
* Uhicellular
lyanophyta
terebrans
Plectonema
pilosa
Calothri
Calothrix crustacea
Dermocarpa sp.
Soirulina sp.
Unicellular blue-greens
Rhodophyta
* Rhodochorton Rothii
Diatoms (
2. The standing crop of the microscopic algae on granite
surfaces is 37 gs carbon/m2 with a production rate of 1.66
carbon/m2/day. Production rate for the algae on the shells
L. planaxis is .981 gs carbon/m2/day. The pigment content
of the algae on the shells is much greater than that of a rock
or Ulva surface of similar size.
3. In 25 days, ten snails reduce the algal pigment content
of a 225 cm2 granite surface by approximately 8% when com-
pared with an ungrazed surface of similar size.
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Bibliography
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diatom populations! Ecology 42: 783-794
the
structure and reproduction
Fritsch, F. E. 1935. The
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------- 1950. The fresh water algae of the United States.
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reen algae of
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Nemoirs of the College of Agriculture, Kyoto University No.83
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