O
The Effect of Certain Environmental Factors on the Activity
Pattern of Littorina planaxis and Littorina scutulata
By Elsa Kops
175h
1964
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Introduction - This study is an attempt to relate
environmental factors to the activity pattern of the two species of
California Littorina, L. planaxis and L. scutulata. The work was
undertaken at Hopkins Marine Station in Pacific Grove during May
1964. All observations were made in the field with the populations
disturbed as little as possible.
From preliminary generalized field observations, the
obvious activities of the animals were determined. Activity was
divided into two phases, actual motion and attachment to the substrate
by the foot. Closure of the operculum and attachment by means of
mucus were equated with inactivity. Feeding, an essential part of any
activity pattern, can be assumed to be associated with motion,
otherwise there would be a rescraping of an area. But differentiation
of feeding motion from other motion was impossible in the field;
therefore this parameter was ignored. Two intraspecific phenomena
were often observed, clustering and pairing, with only L. planaxis
indulging in the latter. The obvious environmental parameters were
degree of substrate moisture, amount of wind, degree of illumination,
and temperature. Tide from the table and time of day were also recorded.
Procedure - From among the granite rocks on which the
Littorina live, three representative areas were selected for
intensive observation: first, a tide pool, surrounded by many crevices
(some water filled) and horizontal and vertical areas, reached only by
the high high tides; second, two small tide pools, on a large
creviced generally horizontal rock group, splashed by the low-high
tides; and third, a surf swept large rock, consisting of a vertical
and horizontal plane, inundated by continual surf for 1.5 hours and
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2.
splashed during the proceding and succeeding hour by the average low
high tide.
For each observation the following were recorded:
time
tide
amount of wind - rated subjectively as none, little, some
General data
strong, very strong
degree of daytime illumination - rated subjectively as
clear, partly clear, overcast
temperature - measured by a thermometer in air, on a rock,
and in water
degree of substrate moisture - estimated by observation as
dry, damp, splash, surf, tide pool
Area data:
population phenomena - clustering, pairing, open or closed
operculum were said to be occuriing when by quick
visual estimation at least 75% of the population
were so indulging
In each area twelve animals (six L. planaxis, six L. scutulata) were
marked and kept track of as individuals. The following were noted:
movement at time of observation - plus or minus
net displacement since last observation - none, 6-2",
2-6", 6-12", more than 12'
open operculum - plus or minus
locale at time of observation - tide pool, edge of tide
pool, crevice, horizontal rock, face, vertical
rock face
change of locale since last observation - minus or
description
18.
Os
clustering - plus or minus
pairing - plus or minus
The data from each group of six were then correlated and graphed,
and the resulting six pages were then clipped to a master graph which
contained the general data. An example of the "book" so formed from
one day's observations is included as Appendix I. These were used as
the basis of graphs attempting to relate individual environmental
factors with specific parts of the activity pattern.
Discussion and Interpretation of Results - The rekability
of the results of this study are limited by three factors: first, the
constant fluctuation of the environment, during a period of observation
the temperature might increase three degrees or a cloud cover the sun;
second, the subjective estimations used to judge the degree of the
parameters; and third, the small number of individuals that can be
kept track of at one time. Therefore the value of the results lies
not in the actual figures obtained, but in the clear emergence of
overall trends.
Moisture effects
On attachment to the substrate by the foot - (Fig. 1) An increase
in moisture produced an increase in percent of animals with foot
attachment. Moisture appears to have a direct effect on this phase
of activity. The 100% activity shown by both species under surf
conditions has definite survival value, it prevents dislodging. Under
all conditions, surf excepted, the L. scutulata showed less activity
than the L. planaxis. The tide pool situation is interesting because
wetness is constant, but the need to hang on is no longer present,
except at high tide. Most of the animals were active, but the 100%
figure shown by L. planaxis is probably not valid. One L. scutulata
781
% of animals
attached to the
suoftraterby
the foot
2 o anmals in
motion atthe
+++

time o

oderatien
% of animals

which have
moyed since
the previous
observation
5 hr.)


k. planavis
. seutata


egreeo
Mamplesh sun
substrate moistur
te

138115
201158 r

degreelof
H
t
substrate moisture
1e Sas
2
a

degree of
eonenpissh srfite

supstrate moisture
17

t
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186
stayed closed in the middle of a pool for several hours and then
opened, thereby accounting for the low figure shown by the L. scutulata
The true percentage is probably in the very high nineties.
On number of animals in motion at the time of observation -
(Fig. 2) An increase in moisture produced an increase in the percentage
of animals in motion at the time of observation. Moisture appears to
have a direct effect on this phase of activity. The lack of movement
on dry surfaces shown by both species was also observed in L. littorea
by Haseman in 1911. Again the L. scutuata showed less activity in all
caught
cases; in fact they were notAmoving until surf conditions prevailed.
For neither species was more than 25% of the population in motion at
any time; this was in agreement with subjective impressions formed
during the early generalized observations.
On number of animals which had moved since the last observation,
1-1.5 hours before - (Fig. 3) An increase in moisture produced an
increase in the percentage of animals which had moved since the last
observation. Moisture appears to have a direct effect on this phase of
activity. In two cases L. scutulata showed a higher percentage of
activity. Movement virtually ceases under dry conditions, but one of
the marked L. scutulata moved. Probably one L. planaxis in the
population moved also, but it did so unobserved, thus allowing L.
scutulata to show a higher percentage of activity. P. W. Glynn in
1963 observed that L. scutulata in the endocladia belt showed a
migration with the tide; these results showed a concurring trend at
a higher level. L. planaxis does not appear to indulge in tidal
migrations. This could explain the higher percentage of activity
shown by the L. scutulata under surf conditions. The percent activity
for splash and surf conditions is basically the same for L. planaxis;
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observations
during which
the populaton

wastpairingt
% of antmals
pairing

of
observations
during which
t
the population
clustering
was
Iftttt
60


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a


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beih spzcizs
lig. 4
degree of
+
substrate moisture
degree
of
substrate moisture
degree of
substrate moisture
activity then increases sharply in tide pools. Maybe for L. planaxis
the splash amount of wetness gives maximum activity; this would protect
from desiccation and allow a larger percentage of activity among the
total population. Whereas L. scutulata, adapted to a lower level,
requires more moisture to attain maximum activity. The difference in
activity of L. planaxis in surf and in tide pools might be accounted
for if the wave force, present in surf action, causes a decrease in
activity. Haseman in 1911 observed that L. littorea became quiescent
during violent splashing by waves. The maximum of three quarters of
the animals having moved since the last observation agrees with the
subjective impression gained during preliminary observations.
On pairing (Fig. 4-5) Correlation of pairing with moisture is
not so evident. In almost all cases of pairing observed under dry
conditions, the animals were observed to cling together, both with
closed operculum, the male attached by dried mucus to the female.
Probably "unpairing" occurs as moisture increases and then some
factor in a good inundation causes a reinterest in the subject.
Moisture has a direct effect, but some other factor or factors
unobserved in this study also may have direct and primary effects.
Fig. 4 indicates the presence of 8% pairing in tide pools, but this
was not on a constant basis. Pairing occurred in the tide pools only
when it was occurringhmong the population as a whole. The pairing
percentages from the individual animals and the population as a whole
correspond quite well.
On clustering - (Fig. 6-7) An increase in moisture produced a
decrease in clustering. Clustering is associated with inactivity. In
most cases the opercula of clustered animals are closed. From the
inverse relationship evidenced here it can be hypothesized that this
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et an mal
Flustering
ok s eet
3e
44123 30
ot antmals
clustering

302
102
28
102
o anmal
attached totthe
substrate by
Ithe foot
H

L.t1, 1S
102


ff
degree
substrate moisture
rig. S
amount of wind
ig.
amount of wind
6.
is a phenomenon directly related to resisting the effects of desiccation,
an adaptation to the niche in which the animals live. Credence is leant
to this hypothesis by the fact that for the first time L. scutulata
showed a higher percentage of indulgence, the difference between the
two species being greatest under dry conditions. It seems logical that
the less adapted L. scutulata would have more need of protection than
the L. planaxis. A third supporting fact is the agreement of both the
individual and population data on the complete absence of the
phenomenon under splash and surf conditions. Periodically the animals
in the tide pools would leave and form clusters in particular places
around the edges; often the clusters would begin under water.
Unsuccessful attempts were made to relate this to data contained in
this study.
Wind effects
These were considered to act indirectly by an increase of wind causing
a decrease in moisture. The desiccating effect of the wind was proven
by the chapping experienced by this observer after days spent in the
field. During the course of these observations the amount of wind
only changed from little to some.
On clustering - (Fig. 8) An increase in wind produced an increase
in clustering, thus adding to the evidence for the protection from
desiccation hypothesis. Again L. scutulata showed a higher percentage
of clustering with the biggest difference between the two species
occurring during the conditions of greatest stress.
On attachment to the substrate by the foot - (Fig. 9) An increase
in wind produced a decrease in the percentage of animals attached by
the foot. The decrease is greatest in L. planaxis which correlates with
the fact that they tend to cluster less and also that they inhabit a
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o antmal
pairing
9 of animals

attached to
the substrate
Ehe oot



50

N2sto2t




++++
158

amountof wind
H
30

30
air tenperature
H


19 + 28
172
16
7.
higher level on the rocky shores.
On pairing - (Fig. 10) An increase in wind produced a decrease
in pairing. This indirect factor seems to correlate better with
pairing than the direct factor of moisture.
Temperature effects
A graph (Fig. 11) relating temperature with attachment to the substrate
by the foot was made. After consideration it is believed that graphing
foot attachment against air temperature is rather meaningless. The
animals in the tide pools are reacting to the temperature of the
surrounding water; each individual on a rock is concerned only with
the temperature of that rock.
Cyclic activity
The moisture-oriented activity pattern shown by the results of this
study would seem to exclude any tidal or circadian rhythm since the
wet-dry cycle doesn't necessarily follow the tides or day and night.
No graphs were made but the correlated field notes were closely
scrutinized and no evidence of rhythms was found for any of the
specific parts of the activity pattern considered in this study.
Haseman (1911) at Woods Hole worked with three species of
east Coast Littorina under the influence of the idea, advanced by
Bohn in 1905, that these animals follow a tidal rhythm. Having found
rhythms correlated with tide level on vertical surfaces only, he
concluded "the primary directed force for rhythmical movements is
the surface film of water" and "Littorina littorea shows no established
rhythm in the absence of tidal changes. Both statements indicate
the lack of a tidal rhythm. It would seem rather that his work proves
that the primary environmental factor effecting the activity of the
East Coast Littorina is moisture.
172
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Summary - Littorina planaxis and Littorina scutulata are
sea creatures adapted to the ecological habitat "uppermost rocky beach.
Their prime problem is prevention of desiccation. Therefore their
activity is correlated with moisture such that under dry conditions
they will be protected by the closed operculum. Factors equaling or
associated with activity (foot attachment, motion, pairing) all
showed an increase with an increase in moisture. Pairing didn't show a
linear correlation, some unknowns are involved. Clustering, an inactive
state,showed an inverse relationship with moisture; from this data it
is hypothesized to function as a protection against desiccation.
Temperature as measured was decided to be a meaningless parameter.
No evidence was found for either tidal or circadian rhythms. Wind
was considered to act indirectly by decreasing moisture. Thus an
inverse effect with foot attachment and pairing and a direct effect
with clustering were observed. An interesting and consistent difference
was shown by the two species. L. scutulata tended to be less active,
to require more moisture before showing activity, and to demonstrate
a higher percentage of clustering.
193
Bibliography
Andrewartha, H. G. Introduction to the Study of Animal
Populations. University of Chicago Press; 1963.
Glynn, P. W. "Ecological studies on the Endocladia muricata-
Balanus glandula association in the intertidal zone in
Monterey Bay. Thesis 1963.
Haseman, J. D. "The rhythmical movements of Littorina littorea
synchronous with ocean tides." Biol. Bull. 21:113 1911.
Hewatt, W. G. "Ecological studies on selected marine intertidal
communities of Monterey Bay." Amer. Midl. Nat. 18:161 1937,
Morton, John Edward Molluscs Harper; 1960 New York.
Newell, G. E. "The bahavior of Littorina littorea under natural
conditions and its relation to position on the shore.'
J. Mar. Biol. Ass. U. K. 37:229 1958.
Newell, G. E. "An experimental analysis of the behavior of
Littorina littorea under natural conditions and in the
laboratory." ibid 37:241 1958.
Ricketts, Edward F. and Calvin, Jack Between Pacific Tides
Stanford University Press; 1960. Stanford, California.
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Appendix
E s ar era e ors ni s d e d etes ase a e e
the graphs. Since this was the second set lof observations
techniques were just being organiaed. Therefore the middie
e was not obsenved in orden to condentrate upon getting
continial data from site d durine ario ot intenaies
action. However this Happened to de the set showing the
mostariation, tnus tis beine used as the-erangle.

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