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Introduction
Persistent diurnal rhythms have been discussed
extensively by many investigaters (Webb, 1950, Behrnes,
1974). Such rhythms have been observed in both physiological
and behavioral processes. (Cloudsley-Thompson, 1961).
Tidal rythms, as well as diurnal rhythms, have been
observed in intertidal invertebrates (see Korringa, 1947).
Sandeen, Stephens and Brown (1956) have noted a
persistent diurnal rhythm of oxygen consumption in two
intertidal gastropods, Littorina littorea and Urosalpinx
cinereus. In Littorina planaxis, two daily periods of
greater oxygen consumption were observed (Lebenzon, Hopkins
Marine Station, Spring report, 1964)
Studies on the general activity of three species
of Littorina, L. scutulata, L.sitkana and L. planaxis
by Behrens (1974) revealed a marked increase in activity
during the hours of darkness. Kops (Hopkins Marine Station,
Spring report, 1964) and Haseman (1911) observed similar
diurnal fluctuations in the activity of L.planaxis and
L. littorea respectively. However, there was no persistence
of these rhythms when the animals were placed under
labortary conditions.
When L. planaxis is suddenly immersed in sea water
by wave action, it responds by opening its operculum,
extending its foot and attatching to the substratum (Bigler,
Hopkins Marine Station, Sprin report, 1964). Preliminary
studies revealed variation in the time required for this
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response. The following is a study of the relationship
of response time to phases of the tidal and diurnal cycles.
Materials and Methods
All snails were collected from the rocky intertidal
at the Hopkins Marine Station, Mussel Point, California.
Animals were taken from a zone approximately five to six
feet above mean lower low water. No attempt was made to
select animals from either horizontal or vertical surfaces,
but all animals were collected within an area of 2-3
square meters.
Response time was measured by dropping the snails
into approximately 10 milliliters of sea water contained
in 1.5 by 15 cm. test tubes. Care was take to assure
that the animals were placed in the water with their
opercula up. Samples of twenty-five snails were used
and the results expressed as the number of individuals
responding within 60 seconds. Tests with five groups
of twenty-five snails, collected at high tide and at
low tide, gave a standard deviation of 3.85 and 3.42
respectively for the 60 second response time.
Results
Measurements of the number of snails responding
within 60 seconds were mde on groups of snails taken
from the intertidal at times corresponding to points in
the tidal cycle over a period of 51 hours. Figure 1
shows the variation in the number responding in these
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sample groups. The mean number responding during the
period of observation was 10.9. Only the low number
responding at dawn on the first day is significantly
different from the rest, due to the high degree of
variability in the number responding at any one point
in time. However, the fluctuation in the number responding
suggests some correlations with aspects of the tidal and
diurnal cycles. The difference between the number responding
at the peaks of the high tide may be due to a difference
in the violence of the waves at the two times. On day
I, the waves were significantly larger than on day 2.
Figure 2 shows a similar measurement of the number
responding during another relatively calm tidal cycle.
In this study, the high tide has advanced by four hours
and a correla tion between the peak number responding and
the high tide is once again to be noted. Although in
Figure 1 the increase in the number responding occurs
before sunset, this increase occurs well after sunset
in Figure 2 suggesting a closercorrelation between the
tidal cycle, rather than the diurnal cycle.
These field studies suggested a relationship between
the number responding and the amount of available moisture
in the high intertidal where L.planaxis occurs. The rising
tide on relatively calm days provides this area with
nonviolent splash.
To test the relationship between fluctuation in the
number responding and fluctuations in the amount of moisture
available, snails were collected at lower, low water, well
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before dawn when the rocks were still damp, and maintained
in the laboratory under conditions of constant moisture
and dim light. Constant moisture was provided by placing
the snails on wet paper towels. One group of twenty-five
were tested immediately. Figure 3 shows the results of
this study. The increase in the number responding occurs
at a time intermediate between that observed in the
studies shown in Fiures 1 and 2 and suggests a possible
correlation with the diurnal cycle, as well as the tidal
cycle.
In a similar experiment, animals were collected
at lower low wwater after dawn and maintained in the
laboratory under conditions of constant dryness. One-half
of these animals were subjected to the constant light
of the laboratory. The other half were placed in constant
darkness and tested usin only a redlight. The presence
or absence of lighthhad little effect during the period
of the experiment. Figure 4 shows these results. Although
the most striking increases in number responding corresponds
to a point in the tidal cycle correlated with high tide
and approaching darkness, Figures 1, 3, and 4 also
suggest another peak of responsiveness corresponding
to the morning hours.
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Discussion
The responsiveness of samples of snails appears to
vary during the tidal and diurnal cycles. There is a
suggestion from the studies reported here that both of
these cycles may influence this aspect of behavior.
A separation of these effects was attempted by studying
animals maintained under conditions of constant dark or
light and constant dryness or moisture. None of these
treatments caused a markedälteration in the behavior
pattern during the time intervals studied. It appears
that studies of longer duration would be required to
further ellucidate the influence of these two cycles.
However, the number of snails required for these long
term experiments would require the use of animals from
a much greater area than that selected as a source for
these studies. This may introduce an even greater vari¬
ablity in the response of the tested groups.
There is a suggestion of two peak times of greatest
responsiveness. One occuring in the morning anc the other
around sunset. The morning peak was also correlated
with lower low water and the evening peak with higher
high water in these studies. These two peaks correspond
to the times of greatest oxygen consumption, as noted
by Lebenzon (Hopkins Marine Station, Student report,1964).
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Summar
1. The number of Littorina planaxis responding
within 60 seconds when immersed in sea water varies
during the tidal and diurnal cycles.
2. Maintainence of animals under conditions of
constant light, dark, dryness or moisture do not appear
to alter the pattern of this variation during periods
of up to 24 hours.
3. Two peak periods of greatest responsiveness
were observed in samples of snails obtained from the
field or maintained as described. One peak period occuned
in the morning and the other around dusk.
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Literature Cited
Bigler, E., 1964. Attrition on the Littorina planaxis
population. Student report, Hopkins Marine Station,
Pacific Grove, California.
Behrnes, S., 1974. Ecological interactions of three Littorina
(Gastropoda, Prosobranchia)along the west coast of
North America, Ph.D. Thesis, University of Oregon. LIl pages.
Cloudsley-Thompson, J.L. Rhythmic activity in animal
physiology and behavior. Acedemic Press, 1961.
New York. 285 pages.
Haseman, J.D., 1911. Therhythmical movements of Littor:
littorea synchronous with ocean tides. Biol. Bull. 21:113-9
Korringa, P., 1947. Relations between the moon and periodicity
in the breeding of marine animals. Ecol. Mono. 17:347-81
Kops, E., 1964. The effect of certain envirnmental factors
on the activity pattern of Littorina planaxis and
Littorina sctulata. Student report, Hopkins Marine
Station, Pacific Grove, California.
Lebenzon,J., 1964. Respiration in Littorinia planaxis and
Littorina scutulata. Student report, Hopkins Marine
Station, Pacific Grove, California.
Sandeen, M.I., Stephens,G.C., Brown,F.A.,Jr., 1954. Persistent
daily and tidal rhythms of oxygen consumption in two
species of marine snails. Physiol Zool. 27:350-56.
Webb, H.M., 1950. Diurnal variations of response to light
in the fiddler crab, Uca. Physiol. Zool. 23:316-37.
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Acknowlegements
I wish to thank Dr. John Phillips for his patience
and helpful advising during the course of the quarter.
I would also like to thank Susan Harris for her encouragment
at a time when I really needed it. I would also like to
thank Linda Baum for her help during the preliminary
studies and for her stimulating conversations at 4:00 A.M.
0
Figure 1
Number of L. planaxis responding within 60 seconds.
Animals taken from the intertidal at points in the tidal
cycle as indicated. Each point represents the number
responding in the sample of twenty-five tested. Vertical
bars indicate plus and minus 1 standard deviation.
—
TIDAL
CYCLE
18
4
2-
L

12 18
12.
TIME



k

—
Figure 2
Number of L.planaxis responding within 60 seconds.
Animals taken from the intertidal at points in the tidal
cycle as indicated. Each point represents the number
responding in the total sample of twenty-five tested.
Vertical bars indicate plus and minus 1 standard deviation.
2271
2
d 1
11
TIDAL
CCLE

kv-

0
12
TIME



—
Figure 3
Number of L. planaxis responding within 60 seconds.
Animals were collected from the intertidal at lower low
water and maintained in the laboratory under conditions
of constant light and constant moisture. Each point represents
the number responding in the sample of twenty-five tested.
Vertical bars indicate plus and minus 1 standard deviation.
12
S lo¬
N 83
2-
TIDAL
/
t-
12
9
15



kkt -
Q 3
21
TME
Figure 4
Number of L. planaxis responding within 60 seconds.
Animals were collected from the intertidal at lower low
water and maintained in the laboratory under conditions
of constant dryness. One-half of those collected were
kept in constant light, and is represented by the solid
lines and dots. The other half was maintained in constant
darkness and tested using red light. These are represented
by the open circles and the dashed line. Each point
for  both conditions of light shows the number responding
in a sample of twenty-five tested. Vertical bars indicate
plus and minus 1 standard deviation.
—
TIDAU
CGE
MA
K.
N


L
4 12 15 18 210 3b 9
TIME
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