J.K.A. U.: Mar. Sci., Vol. 3, pp. 81-90 (1412 A.H./I992 A.D.)
Effects of Temperature on the Oxygen Consumption and
Heart Rate in the Inter-Tidal Wedge Clam,
Donaxfaba (Gmelin)
A.A. ESHKY and M.A. BA~AKDHAH
Facultyof Marine Science,King Abdulaziz University
leddah, Saudi Arabia
ABSTRACT.The effect of temperature on the rate of oxygen consumption
and heart rate has beeninvestigated in the Red Sea, inter-tidal wedge clam
Donax faba. The 010values for both oxygen consumption and heart rate
were often < 2.5 and were relatively constant over a wide range of temperature. This suggeststhat wedge clam is well adapted for life in high temperature environment. It was noted, however, that behavioural mechanisms
were important in reducing the degree of temperature stress that could be
experienced in the field.
Introduction
Donax {aha Gmelin is the most conspicuous member of the sandy beach communities in the Red Seawhere it occupies the wash zone in large numbers (Ba-Akdhah 1989).There are numerous studies on the oxygen consumption in the intertidal
animals, often combined with studies in ventilatory and cardiac activities and
haemocyanin function (see reviews of Mangum 1983; McMahon and Wilkens 1983
and Newell 1979). The effect of body size in gastropodshas been extensively studied
by Berg and Ockelmann 1959; Davis 1966; Huebner 1973; Brown et al. 1978; Rao
and Rao 1984. In addition, the effect of body size on the oxygen consumption of
bivalves has also been studied (Nagabhushanam1957;Lomte and Nagabhushanam
19n; Rao et al. 1974;Mane 1975). Travallion (1965) noted, in particular, the ability
of Nuculasulcata and Nucula turgida to withstand considerable periods of hypoxia.
Taylor (1976) showed similar results for Artica islandica. Wilson and Davis (1984)
81
83
Effectsof Temperature
ments). In order to ensure that the rate of oxygen consumption was unaffected by
hypoxic stress,the oxygen content of the water was never allowed to fall below approximately 80% saturation during a recording.
Rate of oxygen consumption was measured at the following temperatures20, 25,
30, 35°C. As with heart rate, attempts were rpade to obtain data at 40°C but wedge
clams survival was poor and no reliable data were obtainable. Data analysiswassimilar to that described for heart rate.
Results
Heart Rate
The relationship between heart rate and body flesh weight at different temperatures is shown in Fig. 1. The equation for the regressionlines fitted to thesedata are
given in Table 1. Covariance analysisshowed that the slopesof the regressionlines
fitted to the 10°Cand 15°Cdata were significantly different from eachother and from
8
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Total weight (g)
FIG
Relation between heart rate and body total weight of Don~ faba at different temperatures,
10°C-x
25°C-.:
; 15°C-..;
30°C-.;
200C-0
35°C-0
85
Effects of Temperature.
TABLE2. 010values for heart rate of Donax laba
°'0 oyersoCintervals
Total
wt (g)
lO-15°C 15-20"C 1201.96
1.87
4.90
5.06
6.04
5.33
5.14
6.20
1.69
1.83
1.91
1.93
Qloover lOOCintervals
25°C I 25 -30°C
2.95
2.59
3.13
2.68
2.68
2.26
30-3S0C j lO-ZO"C IZO-3O"C !ZS-3SoC
1.41
1.52
1.44
1.38
1.31
1.27
1.63
1.76
1.54
1.53
1.64
1.75
2.90
2.92
3.42
3.50
2.27
3.20
2.19
2.30
2.23
2.03
2.09
1.99
1.51
1.47
1.52
1.46
1.46
1.44
Oxygen Consumption
The changesin aquatic VOz exhibited by wedgeclams acclimated to 25°C and then
exposedto different temperatures within the normal-environmental range (lO-35°C)
are shown in Fig: 3. The regressionequations of the line fitted to these data are presented in Table 3. Covariance analysis of these data showed that there was no sig-
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9
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0.1
02
0.3
0.4
0.5
06
Flesh weight (g)FIG.
3. Relationship between aquatic weight specific rates of oxygen consumption and body flesh weight
of Donax {aba at different temperatures.
200C
-x. , 25°C
-D. , 30°C-O.
-.
, 35°C
Effects of Temperature.
87
speciesof decapodcrustacea(McFarland and Pickens1965;Vernberg 1969;Wallace
1972; Burton et al. 1980; Burggren and McMahon 1981; Morris and Taylor 1985;
Eshky 1985). There is little information, however, on Qrovalues for heart rate in intertidal bivalves. Widdows (1973) demonstrated higher values (2.36-4.21) lor
Mytilus edulis. Lowe and Truman (1972) showed a value of 2.0 for May arenaria.
Truman and Lowe (1971) have obtained a value of 2.16 for tropical Isognonius
alatus. The present study on Donax faba indicates that QIOvalues were lower than
those obtained by Widdows (1973), and similar to those obtained Truman and Lowe
(1971). Within the normal environmental temperature range QIOvalues for heart
rate were closer or less than 2 and in the caseof oxygen consumption QIOvalueswere
slightly higher than 2. Behavioural differencesand the tropical habitat of Donaxfaba
which influence the rate of body temperature may help to explain the differences in
QIOvalues of Widdows (1973)and the presentstudy. Further comparativeinvestigations on the QIOrelationships of the intertidal speciesare neededto clarify the situation and to help explain the discrepancies.
Donax faba rarely experience environmental temperatures below 20°C and avoid
potentially lethal extremes of temperature by behavioural means (Ba-Akdhah
1989). Thus they bury themselvesin the washzone when they face thermal stresses.
This provides a relatively constant thermal environment in which temperatures are
g~nerally between 23°C and 29°C. Outside air temperature near the sand surface
generally varies between 24°C and 37°C. Sand temperature in the wash zone at a
depth of 25 cmremains relatively cool during the day and relatively warm during the
night (Ba-Akdhah 1989). The relatively low and fairly constant QIOvalues indicate
that Donax faba is physiologically adapted to withstand the temperature fluctuations
which oCCurin the washzone environment. There is little comparative information
available for respiration in Donax spp. Some data exist for Donax incarnatus,but
there is wide variation reported of aquatic rates of oxygen consumption in quiescent
clam. McLusky and Stirling (1975)studied the growth consumptionof active Donax
incarnatus from the west coastof India. They showed that the effect of temperature
was considerably less marked than the effect of activity. Their data for the oxygen
consumption rate of an animal of 0.011 g dry flesh weight was0.98 ml °z/g/hr. Widdows (1973), who studied the oxygen consumption of Mytilus edulis from Norfolk,
England, reported the value of 0.60 mVgdryweight/h both setsof data were obtained
at 25°C for active animals. In the presentwork on Donax faba, the meanflesh weight
from our 25°Cdata is 0.,48g and a wedge clam of this weight has an oxygenconsumption of 5.11Lmol°z/g/h. Employing McLu5ky'sformula in its weight specific form a
specimenof Donax incarnatusof 0.011 dry flesh weight and his value of 0.98 ml Oz/g/
h gives an oxygen consumption rate of 43.7 ILmoVg/h,whereasthe equivalent calculation from the data of Davenport (1983) gives a higher value of 82.18 ILmoVg/h.
Widdows (1973) reported a value of 26.8 ILmoVgdry weight/h for Mytilus edulis at
25°C: There are wide variations in the values of the slope 'b' in the equation VOz =
awb-I where VOz is the weight specific rate of oxygen consumption. Davis (1966)
adapted a common regression coefficient oj -0.69 for the weight specific oxygen
consumption of Patellaspp. Brown etal. (1978)reported a value ofO.5621.forBuliia
spp. Ganapati and Rama (1975)reported a value of 0.54 for the speciesTurbo inter-
Effectsof Temperature.
89
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