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Cynthia Lebsack
INTRODUCTION
The chiton Mopalia lignosa (Gould, 1848) is a common
inhabitant of the inter-tidal zone on Californian shores.
Although it usually retreats to sheltered regions during
the day and at low tide, it must be able to cope with
relatively wide variations in temperature and salinity,
both on a seasonal basis and during a single tidal cycle.
Temperature and salinity in the environment do not necessarily
fluctuate together. In winters, for example, animals may
experience relatively high salinities and low temperatures
when submerged, and low salinities and low temperatures
during rains at low tide.
Studies of the combined effects of temperature and salinity
on metabolic rates have been carried out on such marine
organism as the crabs Hemigrapsus oregonensis Dana, 1851)
and H. nudus (Dana, 1851) by Dehnel (1960), and the gill
tissues of oysters and mussels by Van Winkle (1968).
However, no studies of this sort have been made on chitons.
I here report the effects of simultaneously imposed
temperature and salinity variations on the respiratory
rate of M. lignosa. All studies were carried out at the
Hopkins Marine Station of Stanford University, Pacific
Grove, California, during the period April-June, 1974.
The chitons used in the experiments were collected at various
points on the rocky shores of the Monterey Peninsula.
Cynthia Lebsack
page 3
MATERIALS AND METHODS
Respiration rates were measured using Warburg-
Barcroft manometers kept in a water bath held at a
constant temperature. A wick of filter paper wetted
with 0.2 ml of 10% KOH was placed in the side arm
of the respiration chamber in order to absorb C0», and
the vessels were agitated. The vessel constants were
measured using a Gilmont-Warburg calibrator.
Salinities were obtained by dissolving "Instant
Ocean Synthetic Sea Salt" (Aquarium Systems, Inc.).
in appropriate amounts of distilled water and were
checked with a salinometer. Normal sea water from
the environment (100%) was determined to be 33.91%.
Animals taken from the field were held in running
sea water at 13.510.5°0 for at least three days
before use. I assumed the relation between respiratory
rate (Vo2) and body weight (W) followed the equation;
Voz-Kw0.74 where K is a constant. The value 0.74
is the generalized value for animals given by Prosser (1973)
and is close to the average value (0.73) found by
Kincannon (1974) for the chiton Tonicella Lineata
(Wood, 1815).
Using the above equation, the measured respiratory
rates were corrected to that of a hypothetical ten
gram chiton. The weight of the animals varied from
5.5-18.5 grams. Sample size varied from three to
six animals at each temperature salinity combination.
Cynthia Lebsack
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Individual chitons were placed in separate Warburg
vessels and covered with seventy ml of synthe tic
sea water at the salinity to be tested. They equilibrated
for one hour at a given temperature. Readingswere
then taken hourly for six hours. The average number
of ul of 0 consumed/gram/hour was taken as the
respiratory rate. Each of the three temperatures
within the environmental range encountered by M. lignosa
(800, 13.500, and 19°0) was combined with four different
salinities (90%,100%, 110%, and 120% of normal sea water)
to yield separate experimental conditions.
Kincannon (1974) has shown that there is not
conspicuous diurnal rythm in regards to chiton respiration.
thus experimental runs were made at various times during
a day.
RESULTS
Respiration rates vs. temperature for the four
salinities are shown in Figure 1. Their 010 values
are listed in Table 1. Like most poikilotherms.
chitons respire at an increased rate at higher temperatures:
go
as.
gar ou
36.2 ul at 100% sea water and 190C ys. 14.27 ul at
100% sea water and 800. The 010 value calculated
using the 13.5°0 and values for animals in 1906 and 100 %
sea water is 2.0. However, using the 80C and 13.50C values.
a much higher 910 of 2.7 is obtained for the same animals.
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Cynthia Lebsa
Respiration as a function of salinity for each
experimental temperature is plotted in Figure 2.
For each temperature, animals in 100% SW respired at a
significantly higher rate than at any other salinity.
DISCUSSION
Most marine molluscs are osmoconformers with
varying degrees of stenohalinity (Prosser, 1973).
Kinne (1971), states that although not much is known
on how salinity affects invertebrate metabolism,
there are some general trends in the responses of
species. One of these trends is that animals which
are stenohaline decrease respiration at both the
higher and lower salinites. This reduction in respiratory
rate may be mediated through any of the following
routes: (1) increasing or decreasing the body water
or salt content; (2) changing of internal ion ratios;
(3) hormonal, neuromuscular, and enzymatic interference
and (4) behavioral changes (Kinne, 1971). In addition
there is probably a reduction in the concentration
of cellular metabolites in animals placed in hypotonic
solutions, and a reduction of oxygen tension in those
exposed to hypertonic media, both of which could lower
respiratory rate.
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Cynthia Lebsack
The least change in respiration due to osmotic stress
was found, in both hyper and hypoosmotic solutions,
at 8°0. Perhaps at this temperature the metabolism
is nearly minimal for maintenance, and the chiton
actively controls against further lowering.
In 100% sea water the Qjobetween 8°0 and 13.5°0 is
higher than that between 13.5°0 and 1900; this agrees
with many observations on other animals that Q0 decreases
with increasing temperature (Prosser, 1973). The
Qio's increase from the lowest salinity to the highest
for the colder temperature interval but remain quite
constant at the higher temperature interval (Table I).
Work should now be done to elucidate the physiological
processes responsible for this low temperature change
of 9jo with salinity.
SUMMARY
1. Mopalia lignosa respire at a higher rate as the
temperature increases.
2. Deviation in salinity from normal sea water causes
a decrease in respiration rate.
3. At low, but not higher; temperatures, the 910
increases with salinity.
Cynthia Lebsack
page 7
Acknowledgments
I would like to extend a sincere thanks to
Christopher Harrold for his instruction on use of the
Warburg, to Dr. Robin Burnett for his patience and help
with statistics, and to Charles Baxter for his advice.
aide, and encouragement on this project. To the staff
and students of Hopkins Marine Station thank you for
making this academic pursuit such an enjoyable one.
Temp & Salinity Effects on Respiration, Mopalia lignosa page8
Lesback
LITERATURE
CITED
Dehnel, Paul A.
1960. Effects of temperature and salinity on the oxygen
consumption of two intertidal crabs. Biol. Bull. 118(2): 215-49;
215-49; 10 figs.
Kincannon, Elizabeth A.
1975. The relations between body weight and habitat temperature
and the respiratory rate of Tonicella lineata (Wood, 1815)
(Mollusca-Polyplacophora)
Kinne, otto
1971. Salinity: animals—-invertebrates. Pages 821-995 in
Otto Kinne, ed. Marine Ecology. Vol. I, Part 2. New York,
N.Y. (Wiley-Interscience)
Prosser, Clifford Ladd, ed.
1973. Comparative animal physiology. xxii + 966 + xly
pp.; illus. Philadelphia, Penn. (W. B. Saunders Co.)
Van Winkle, Webster, Jr.
1968. The effects of season, temperature and salinity on the
oxygen consumption of bivalve gill tissue. Comp.
Biochem. Physiol. 26(1): 69-80; 5 figs.
(28 December 1967)
e
Lebsack
TABLE 1
values for the intervals 8°-13.5° C and for 13.5
C, for the four test salinities.
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o-19°
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Cynthia Lebsack
FIGURE CAPTIONS
Figure 1 - Mean oxygen consumption vs. temperature at salinities
of 90%, 100%, 110%, and 120% sea water.
Figure 2 - Mean oxygen consumption and standard errors vs.
salinity at 8° C, 13.5° C, and 19° C. Letters next to
individual data points indicate significant
differences, using student's C-test, from 100%
S.W. values obtained at the same temperature.
=)p K.025; Cp.05.
A2p.005;
c
Cynthia Lebsack
TABLE 1 - (
Values
TEMPERATURE INTERVAL
8°c - 13.5° c
Seawater
1.5
90%
2.7
100%
110%
3.0
3.4
120%
13.5° c - 19° c
2.1
2.0
2.0
3.0
S

8 3
8
8 8
—



8