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PLEASE TYPE ABSTRACT DOUBLE SPACED BELOW
ROGERS, DON A. (Hopkins Marine Station, Pacific Grove,
Calif., USA.) The effects of light and tide on movements of the
limpet Acmaea scutum (Gastropoda: Prosobranchia) The Veliger
--Acmaea scutum moves most when subject
to the turbulence of the tidal wash during tidal ebb and flow, but
continues to move when submerged at high water. A. scutum moves
upward with the incoming wash during tidat flow and downward with
the outgoing wash during tidal ebb. The movements of A. scutum
during periods of wash appear to be dependent on the light conditions;
vertical and total movements are greater at night than during the
day. In the laboratory A. scutum moves upward when submerged; the
rate is slowest when animals are illuminated from above, higher
under conditions of darkness, and still higher whenrthenanimais are
balou
illuminated from as.
PLEASE DO NOT TYPE BELOW THIS LINE
6
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The Effects of Light and Tide on Movements
of the LimpetAcmaea scutur
(Gastropoda: Prosobranchia)
By
Don A. Rogers
Hopkins Marine Station of Stanford University
Pific Grove, California
(4 Text Figures, 1 Table)
The limpet, Acmaea scutum Eschscholtz, 1833, inhabits the
midtide zone on rocky shores along the California coast. Test
(1945) has noted some aspects of the ecology of this species, but
detailed information is lacking on its activity pattern. The
present study was undertaken to determine the movements of the
Acmaea scutum population and the effects of tide and light on
these movements.
Field Study
Methods and Materials
Except where noted, all studies were carried out on the
rocky shores of Mussel Point, Pacific Grove, California. Two
vertical rock surfaces, located on the leeward side of Mussel
Point were chosen for the first set of field studies. Both
surfaces faced west and both were exposed to considerable surf.
To facilitate the measurement of limpet movement, narrow horizontal
lines were painted on botherock surfaces approximately one foot
above the highest A. scutum. One inch divisions were marked along
this line. The A. scutum were individually marked by dots of paine
on their shells. Marking was done at low tide on a warm day, and
the animals were not removed from the rock. The horizontal
Footnote 1
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Don A. Rogers 2
positions of the marked limpets were indicated with reference to
the divisions on the horizontal line; vertical positions were
measured with a yard stick. Further painted lines on the rock
were avoided because it was felt they might ffect limpet movements.
On April 27 and 28, 1966, the positions of nineteen Acmaea
scutum were recorded avery hour or every two hours for a twenty-
four hour period. On May 3 and 4, 1966, the positions of eleven
other A. scutum were recorded hourly for a twenty-four hour period.
The light conditions and the level of the tide were recorded with
each observation. At each observation it was noted whether the
limpets were submerged by the sea, awash, or exposed to the air.
the term Aawash" covers all conditions between the first dampening
of the animals by splash to completé submersion.
The positions recordedfrom the field observationswwere
plotted to scale on graph paper. The resulting points for each
.7.
h to provide atrack
metwere connected withs.
nimum net displacement in successive intervals of
ndicating
ime. Preliminary observations showed that the marked Acmaea scutum
were underwater about sixteen hours a day. A wet suit, snorkel,
mask, and underwater light were used to observe the limpets when
submerged. During the period of higher high water on both days
the heavy surf conditions made observations impossible.
Individual Tracks
Of the thirty Acmaea scutum marked in the two areas, six
were either washed away or had their paint makksrremovedbbytshe
water. All of the remaining twenty-four Acmaea scutum moved during
the twenty-four hour observation periods. Earlier observations
376
Don A. Rogers 3
had indicated that A. scutum moves very little when out of water.
For this reason the intervals between successive observations were
greater when the animals were out of the water. Figure I shows
the trails of two A. scutum as plotted from positions recorded
every hour or every two hours. In Table 1 I have tried to show
the percentage error in my tracking method. Without contindaas
observations one cannot be certain of the exact path the limpet
followed to reach the new point. Table 1 shows that there is an
apparent decrease of 15% in the trail length if one records
positions every two hours rather than once every hour. Even with
hourly readings the distances represented by the recorded tracks
are probably less than the actual distances moved, but the limpets
move so slowly that the error is probably small. The trails of
the two limpets shown in Figure 1 are characteristic of the trails
of all the marked A. scutum. The trails demonstrate that individuals
cross one anothers tracks during periods of activity. Figure 2
shows that between successive periods of lower low water A. scutur
moves an average of 40 inches with extremes of 16 and 76 inches.
While plotting the trails of the twenty-four limpets it was
noticed that at low tide they returned to the vicinity of the spot
they had occupied the previous low tide. The average net displace¬
ment of the twenty-four limpets from one low tide to the next was
ang one o
5.5 inches. The largest net displacement for the twenty-four limpets
axaca
was 14 inches. Only one of the twenty-four returned to the samer
et spot it had occupied the previous low tide, and here it
assumed its original orientation. Subsequent observations at
37
372
Don A, Rogers 4
coufrd
Cypress Point, Pebble Beach, California, sppeed the general obsvvalbt
ferd
that
e individuals, to return to a spot near that occupied at
the previous low tide. Combining the net displacement figures
with the data in Figure 2 shows that A. scutum moves an aveyage
of 40 inches between low tides but the average net displacement
is 5.5 inches.
...
Movements In Relation to Tide and Light
In an attempt to find a relationship between tide, light,
and the movements of Acmaea scutum the total houly movement and
the vertical vector of the hourly movement were compared at
ferent phases of the tide and under different light conditions.
—
The total hourly movement is the distance between the posicions
occupied by a limpet before and after a one hour interval. The
vertical vector of the hourly movement is the vertical separationn
of the limpet's positions before and after a one hour interval. The
elation of total and vertical movement to light and tide is
represented in Figure 3 for the two observation areas. The A. scutu
represented in Figure3, A, were uncovered by the tide only once
during the twenty-four hour watch. The A. scutum represented in
igure 3, B, were uncovered twice during the twenty-four hour watch.
Figure 3 shows that Acmaea scutum moves most when it is awash.
Each peak on the graphs showing total movement corresponds to a
period when the animals werenawash. A. scutum does not move when
Aher
out of the water and in sunlight, but the animal may move a
dedarce
a during the day when out of the water in the shade. When
completely submerged A. scutum moves sporadically, and the effects
Don A. Rogers 5
of light and darkness on movementjunder theseconditions appear
negligible.
The graphs showing the vertical component of movement (Figure 3)
demonstrate that Acmaea scutum moves upward when washed by the
incoming tidedand downward when washed by the outgoing tide. The
light conditions during the period of wash appeam to affect the
distance A. scutum moves. In Figure 3, B, when the incoming wash
was accompanied by sunlight, both the total and the vertical move¬
ments were much less than when the incoming tide was accompanied

by shade. The effects olflight and darkness on the vertical move¬
ments of submerged animals are difficult to evaluate from these
field studies.
Laboratory Studies
To test the correlation of Acmaea scutum movements with the
conditions of tide and light as found in the field, several
laboratory experiments were made. Preliminary studies showed that
when submerged in laboratory aquaria A. scutum generally moves
upward. It was decided to test the effects of light and turbulence
on this movement. Turbulence was chosen as a variablei in addition
to light, because the field studies had indicated that A. scutu
moves most when awash. A 20 inch by 7 inch glass plate was placed
rtically in an 18 inch deep glass cylinder (diam 8 inches).
Light was provided by a 100 watt bulb placed directly above or
directly below the glass cylinder. In all of the experiments aif
esied
was bubbled through the water, but where turbulence was neicaced
two bubblers were placed in the cylinder and the compressed air
flow was increased to the point where the surface of the water was
32
Don A. Rogers 6
vigorously agitated. In each experiment 12 to 16 A. scutum were
placed on each side of the glass plate about one inch from the bo
bottom. Each experiment was run twice; a total of approximately
50 limpets were subjected to each combination of variables for a
period of two hours.
The results of the experiments are shown in Figure 4. The
is fou bars ofthgap
epresent the combinations of
variables most closely approximating thase in the field. In the
rial with light above the cylinder and calm water the fewest
npets reached the surface. This result corresponds well with
the field observation that Acmaea scutum move upward only a

ssance
a when they are awash on a resing tide during the day. Of
the first four experiments, the greatest number oflimpets reached
the surface under conditions of darkness and turbulence. This result
rrelates well with the field observation that A. scutum move
co
upward most rapidly when they are awash on a rising tide at night.
Preliminary studies showed that, when submerged, Acmaea scutum
exhibits a negative geotaxis, and moves upward. Ross (1966) found
ged A. scutum also exhibit a negative phogotaxis. In the
that subme.
st four experiments it appears that these two responses are
operating. When animals were submerged in the light, the negative
responses to light and gravity opposed each other, and only 40% of
the limpets reached the surface in the two hour period. To test this
interpretation the light was placed beneath the cylinder in the last
two experiments. Under these circumstances the negative taxes to
gravity and light reinforced one another and more than 80% on the
limpets moved to the su?
a in the two hour period.
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Don A. Rogers 7
Summary
1) The effects of light and tide on the movementsorithe
limpet, Acmaea scutum were studied in the field and in the laboratory.
2) A. scutum moves most when subject to the turbulence of the
g tidal ebb and flow, but continues to move when
idal wash u
submerged,at high water.
3) A. scutum moves upward with the incoming wash during tidal
flow and downward with the outgoing wash during tidal ebb.
4) The movements of A. scutum during periods of wash appear
to be dependent on the light conditions; vertical and total move-
nents are greater at night than du
ing the day.
5) In the Sield situation studied A. scutum moved an average
of 40 inches between two successive periods of lowerglow water,
but returned to within an average distance of 5.5 inches from the
starting point.
6) In the laboratory A. scutum moves upward when submerged;
the rate is slowest when antmals are illuminated from above, higher
under condition of darkness, and still higher when the animals are
Cangin
illuminated from below. These results generally set results
obtained in the field, and are interpreted in terms of a negative
geotaxis (stronger) and a negative phototaxis (weaker) in limpets
awash or submerged.

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Don A. Rogers E 8 370
Acknowledgements
This work was made possible by Grant GY806 from the Undergraduate
Resa
hPart
icipation Program of the National Science Foundation.
The author also wishes to thank Dr. Donald Abbott for his advice
e en
and assistance in the execution of thes-papor.
Don A. Rogers 9
Literature Cited
Grant, Avery (Test)
1945. Ecology of California Acmaea.
Ecolog
26 (4): 395-405
Ross.
Thomas
1966. Light responses in the limpet Acmaea li
natula.
The Veliger
1) ermanent address:
Footnotes
Don A. Rogers 10 878
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Don A. Rogers
TABLE CAPTION
Table 1. Differences in trail length recorded when positions of
limpets were measured every hour vs. every two hours.

379
O
Individual
A. scutu
Total

ae

2T.
DI
—
Observed
every
hour
286
242 - 859.
286
racked (Inches!
—
Observed
every two
hours
42
24.
242

C
3
Don A Rogers 12
Don A. Rogers 8 1388
ae
Figure,Captions
Figure 1. Trails of two Acmaea scutum on a vertical rock surface
during periods of awash and submersion from 1500, April 27, 1966.
to 0900, April 28, 1966. Each point represents the position of
the limpet at the time of observation.
Figure 2. Total distance moved by twenty-four Acmaea scutum on a
vertical rock surface during a 24 hour period.
Figure 3. Comparison of light and tide conditions with total movement
the
and,vertical component of total movement. Figure33 A refers to data
collected April 27-28, 1966, from the movements of sixteen limpets.
Figure 3 B refers to data collected May 3-4, 1966, from the movements
of eight limpets. Time is represented on the horizontal axes of
both graphs. The vertical axes of the upper graphs, showing total
hourly movement, represents the total distance moved during the
hour for all of the limpets. The veticallaxes of the lower graphs,
tho
showing vertical component of movement, represent the upward or
downward displacement each hour of all the limpets from the position
they had occupied at the beginning of the hour period.
Figure 4. Results of labokatory experiments. Each experiment lasted
two hours. The top graph shows the percentage of limpets that were
at the surface after the two hour period. The middle graph shows
the percentage oflimpets that were between the bottom of the glass
plate and the surface after the two hour period. The lower graph
shows the percentage of limpets that were still at the bottom of
the glass plate after the two hour period.
0
OS
t of observation period
End of observation period



Tin.



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tide mark
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.
Don A. Rogers
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42
21

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19

- 33- 41-49- 5/- 65- 73-
16-2
24 32 40 48 56 64 72 80
Total Inches Traveled
in 24 Hour.
—
Gigare
Don A Roge
38
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Conditions of Ex
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Don A Rogers 7
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