AODITONAL INEORMATION, IE ANV, CONCERMNG AUTHORS, ADORESS, TTLE. OR CIATON DAIA
PLEASE TYPE ABSTRACT DOUBLE SPACED BELOW
Baldwin, Simeon (Hopkins Marine Station of Stanford Univ., Pacific Grove,
Galif., U.S.A.) Manometric measurements of respiratory activity in
Acmaea digitalis and Acmaea scabra. The Veliger
Respiration in two species of limpets, Acmaea
digitalis Eschscholtz, 1833 and Acmaea scabra (Gould, 1848), was stud-
ied by means of Warburg manometers. In both species it was found that
the maximum respiration rate occurs when the animal is submerged, and
the least occurs when it is exposed to air. Under damp and aerial con¬
ditions A. scabra showed a much lower rate of respiration than did 4.
digitalis. Under conditions of increasing temperature from 10° to 250c,
A. scabra increased its respiratory rate approximately 60%. A. digitalis
rate increased 23% from 10° to 20°, but at 25° its rate had decreased to
less than that at 10°c.
PLEASE DO NOT TYPE BELOW THIS LINE
28
Manometric Measurements of Respiratory Activity
in Acmaea digitalis and Acmaea scabra
(mollusca: Gastropoda: Prosobranchia)
Simeon Baldwin?
Hopkins Marine Station of Stanford University
Pacific Grove, California
(3 Text figures; 2 Tables)
Both Acmaea digitalis Eschscholtz, 1833 and Acmaea
scabra (Gould, 1848) spend a considerable proportion of
the day exposed to the dessicating elements of the en¬
vironment. Several field studies have shown that, although
the two species are always found in close proximity, above
about the +5 foot level of the intertidal, A. scabra is
usually the only species found on exposed horizontal rock
surfaces (Haven, 1964).
This difference in exposure sug¬
gests possible physiological differences between the two
that might be revealed by respiratory studies. To deter¬
mine such differences, laboratory measurements of oxygen
consumption were made under varying conditions of temperature
and dehydration. The results showed a significant differ¬
ence in metabolic rate between the two species, as well as
differences in submerged and aerial respiration rates.
* Footnote
26
Simeon Baldwin
Methods
Respiration rate was measured with Warburg-Barcroft
manometers in a refrigerated water bath. Carbon dioxide
was absorbed in the vessel side arm using 0.3 ml of a
30% KOH solution, with a wick of starch-free Whatman's
The vessel constants for each run were
+40 filter paper.
determined for the conditions of the experiment, the var¬
iables being the experimental temperature, volume of
flask contents, and the volume of the flask plus manometer
arm. The latter was determined by Umbreit's method of
calibration with water (Umbreit, 1945), and the approp¬
riate vessel constants then found from Dixon's nomogram
(Dixon, 1951). During each run the vessels were agitated
at the rate of approximately 60 - 70 oscillations per min¬
ute. The experiments were done during April and May, 1966.
The organisms used were medium sized A. scabra and
A. digitalis collected about 1 hour before low tide from
the +4 to +6 foot region of the intertidal zone near Hopkins
Marine Station They were then transferred to aquaria
supplied with running seawater at 15°C where they were al¬
lowed to equilibrate for at least 24 hours before being
tested.
Submerged and damp runs were made with animals temper-
ature-equilibrated for 3 hours before the experiment in a
finger bowl in the water bath. Animals used for determin¬
ing submerged respiration rates were then placed in the
Warburg vessels and covered with 6 ml of millipore filtered
Simeon Baldwin
-3
seawater. Animals used for determining damp respir¬
ation rates were shaken to remove excess filtered sea¬
water and then placed in dry flasks. Animals used in
aerial runs (no water included in Warburg vessel) were
placed foot down on a stack of 6 paper towels for 3.5
hours at room temperature (approximately 22°C) before
being placed in the dry vessel. With this proceedure
they were still able to attach to the sides of the vess¬
els.
For each experimental variable, animals were collect¬
ed under the same conditions and subjected to the same
treatment in order to minimize variables. Five separate
vessels were used containing 3 limpets per vessel.
Each run was repeated a minimum of three times using diff¬
erent animals so that each rate is an average of approx¬
imately 45 similar-sized animals taken from the same inter-
tidal area.
All respiratory measurements reported were made in
the dark, since preliminary runs measuring aerial resp¬
iration of A. scabra showed that photosynthesis of algal
growths on the animals' shells was producing signific¬
ant amounts of oxygen. Measurements of respiration of
empty limpet shells in the dark showed that the volume
of oxygen consumed was about 0.05% of the total amount
used by limpets during a 2 hour run. This negligible
amount was therefore not taken into consideration in the
28
Simeon Baldwin
-4-
final rate calculations.
In all experiments shell sizes of animals used were
14 - 17 mm in length. Dry weights were determined by re¬
moving the shell and drying the animal to constant weight.
Rates are expressed in ul 0, per mg dry weight.
Results
Respiration rates of the two species as related to the
and talli 1.
state of their environment are shown in Figure 1, This
depicts average oxygen consumption at 30 minute intervals
during the two hour measuring period. It is seen that the
damp and aerial respiration rate of A. scabra is consider¬
ably less than the submerged rate, the submerged rate being
2.25 times greater than the damp rate, and 4.36 times great¬
er than the aerial rate. By contrast, it is apparent that
the respiration rate of A. digitalis is not so markedly
affected by these conditions, the submerged rate being only
1.12 times greater than the damp rate and 1.42 times greater
than the aerial rate. It is also seen that although the
rate of submerged A. scabra is slightly greater than the
submerged A. digitalis rate, the damp and aerial rates of
A. digitalis are greater than the damp and aerial rates of
A. scabra.
and tatle 2.
Figures 2 and 3,depict respiration rates of submerged
A. scabra and A. digitalis as a function of temperature.
In these experiments, the same group of animals was used
89
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Simeon Baldwin
for the different temperatures, and they were equilibrat¬
ed for three hours at the experimental temperature before
being placed in the Warburg vessels. In A. scabra (Fig. 2),
it is seen that although respiration rate generally in¬
creases with temperature, it is not very pronounced; the
initial rate increasing only about 60% in going from 10°
to 25°C. It is also seen that that in A. digitalis (Fig. 3),
the respiratory rate is again relatively insensitive to
temperature, and between 20° and 25°C it actually drops to
a rate less than was found at 10°C. This same drop of
rate between 20° and 25°C was observed whether the first
measurements were made at 10°, then 15°C, etc., or whether
the first measurements were made at 25°, then 20°C, etc.
Discussion
Respiration Under Varying Exposure to Air
The data indicate that in both species the maximum
rate of respiration occurs under submerged conditions and
the minimum rate under aerial conditions. In both species
the rate during damp conditions falls between that of sub¬
merged and aerial.
A. scabra showed a much lower rate of respiration than
A. digitalis under damp and aerial conditions, a finding
which suggests a possible mechanism for conservation of
food reserves while out of water. This also fits in with
80
Simeon Baldwin
White's observations on glycogen content of high and low
forms of A. scabra (White, 1966).
All animals of both species were chosen with a similar
(thont shett
shell size, but the mean weight, of A. scabra was later
found to be 23 mg as compared to 59 mg for A. digitalis.
This could account for the finding that A. scabra had a
higher submerged rate than A. digitalis in that it
may be a reflection of a higher surface to volume ratio
for the former, rather than a higher metabolic rate.
Respiration Under Varying Conditions of Temperature
The increased respiratory rate at higher temperatures
was not as great as would be expected on thermodynamic
grounds. The reason for this is not known. The marked
drop in submerged rate of A. digitalis between 20° and 25°(
is interesting, since A. digitalis has a lethal temperat¬
ure during prolonged exposure of around 32°C (Hardin, 1966).
It is possible, therefore, that the decreased respiratory
rate is related to physiological derangements leading to
death. As no such decrease was observed in A. scabra, it
would appear that it is better suited to withstand elevat¬
ed temperatures than is A. digitalis. This finding also
agrees with the field observations on distribution, and
the lower tolerance to high temperatures of A. scabra as
compared to A. digitalis (Hardin, 1966). Southward (1958),
in a study on intertidal animals, found that during expos¬
ure to increasing temperature, the animal's activity was
Simeon Baldwin
was the first and most sensitive body function to be
affected. This would be reflected in a decreased resp¬
ation rate as the critical mortality temperature was app¬
roached. Further measurements at closer increments from
15° through 30° should be made in order to determine the
exact point of rate decrease and the maximum tolerable
temperatures for both of these species.
In these limited laboratory observations it was im¬
possible to take into consideration daily and tidal
rhythms in respiratory rates that almost certainly were
present (Sandeen, Stephens and Brown, 1958). Other un¬
controlled variables that might have influenced the ob¬
served results are body weight and nutritional state of
the animals, since the intervals between last feeding and
respiratory measurements were unknown.
Summary
Respiration in two species of limpets, Acmaea digitalis
Eschscholtz, 1833 and Acmaea scabra (Gould, 1848), was
studied under varying conditions by means of Warburg
manometers. In both species it was found that the max¬
imum respiration rate occurs when the animal is submerged,
and the least occurs when it is exposed to air.
Under damp and aerial conditions A. scabra showed a much
lower rate of respiration than did A. digitalis. Under
conditions of increasing temperature from 10° to 25°c,
32
Simeon Baldwin
-8
A. scabra increased its respiratory rate approximately
from 10° to 20°0
60%. A. digitalis' rate increased 2
but at 25° its rate ! decreased to less than that at
10°c.
33
Simeon Baldwin
Acknowledgements
This work was made possible by Grant GY806 from the
Undergraduate Research Participation Program of the
National Science Foundation. The author also wishes to
thank the faculty, staff and graduate students of the
Hopkins Marine Station for their unending encouragement
and assistance.
34
FOOTNONTES
"Footnote 1, page 1 - Permanent address:




S. Baldwin
3.
Simeon Baldwin
Literature Cited
Dixon, Malcolm
1951. Manometric methods as applied to the measurement
of cell respiration and other processes.
Cambridge Univ. Press; vii-xii + 161 pp.
Hardin, Dane
1966. A comparative study of lethal temperatures in
the limpets Acmaea scabra and Acmaea digitalis.
The Veliger
Haven, Stoner H.
1966. Personal communication (Lecture delivered at Hopkins
Marine Station, April 18, 1966).
Sandeen, M. I., G. C. Stephens, & F. A. Brown, Jr.
1954. Persistent daily and tidal rhythms of oxygen
consumption in two species of marine snails,
Physiol. Zool. 27: 350-356.
Southward, J. J.
1958. Note on the temperature tolerances of some inter¬
tidal animals in relation to environmental temperatures
and geographical distribution. Journ. mar. bio. Ass.
U.K. 37: 49-66.
Umbreit, W. W., R. H. Burris, J. F. Stauffer,
1945. Manometric techniques and related methods for
the study of tissue metabolism. Minneapolis, Minn..
Burgess Publ.; 1-198 pp.
36
Slmeon Baldwin
Litorature Citod Cont.
White, T. Jeffery
1966. Motabolic activity and glycogen stores of Acmaea
scabra. The Veliger
Zeuthen, Eric
1947. Body size and metabolic rate in the animal
kingdom with special reference to the marine micro¬
fauna. Compt. rend. Lab Carlsberg, Sér. chim. 26 (3):
16-161.
Simeon Baldwin
Captions
Figure 1: Oxygen consumption of A. digitalis and
viryinq degre
A. scabra undervaryingsenditiens-eex-
hydration
pesuretoair.
Oxygen consumption of A. scabra undevar
Figure 2:
dicert
ingendiof temperature
Oxygen consumption of A. digitalis undervary-
Figure 3:
dent
inondtionsof temperatures,
Table 1:
Oxygen consumption of A. digitalis and A.scabra
varvin degees o hydaton
at
underaryingonditionsofexposurete-air.
Table 2:
Oxygen consumption of A. digitalis and A. scabra
+mpatures.
decern
under varying condittons of temperature.
8
gore 1.
-1.6 ul
1.4
1.2
-1.0
-0.8
-0.6
0.4
0.2
— Acmaea scabra
----- Acmaea digitalis

60
120
Time (Minutes)
3.
Fijore 2.
-1.0
-0.8
0.6
-0.4 5
-0.2

60
Time (Minutes)
—
120