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Metabolic rates of marine bivalve molluscs determined by calorimetry
METABOLIC
RATES OF MARINE BIVALVE DETERMINED BY CALORIMETRY
MOLLUSCS
C. S. HAMMEN University
of Rhode
Island.
(Rewired
Kingston.
R102881.
U.S.A
19 June 1978)
Abstract-l. Rates of heat production (QH) of four species of marine bivalve molluscs. a gastropod. and a decapod crustacean were determined with a heat-retention. differential calorimeter. 2. Rates of oxygen consumption (Qo) of the same animals were determined by standard manometric methods. 3. QH varied with species from 1.6 to 6.2 J/hr per g tissue. and Q. from 1.8 to 4.1 pmol/hr per g. 4. The bivalve MW urmariu. the gastropod Littorinu litrorru, and the decapod Lihiu duhiu had ratios of QH/Qo equal to 0.462. 0.434. and 0.477. respectively. which agree closely with the ratios of AH/A0 for combustion of common food substances. 5. The ratios Q,,/Qo for Mytilus edulis. Mrrcwuric~ rwrcmuria. and Crmsostwtr kyinica were 0.635. 1.15. and 3.40. respectively. which indicate Q. was too low to represent accurately the total metabolism of these species.
INTRODUCTION
Direct calorimetry has been used very little as a measure of metabolism of marine invertebrates because of the greater convenience and sensitivity of oxygen-consumption methods. However, many animals not only tolerate but normally enter anaerobic states, during which rates of oxygen uptake are near zero (Hammen. 1976). The conversion of labelled substrates into other substances indicates that intermediary metabolism continues unabated in many species during early phases of anoxia (Ellington & Hammen. 1977). Aerobic and anaerobic metabolic rates of marine mussels of the genus Mjtilus have been compared by two methods. From tissue concentrations of ATP and related nucleotides, a high fraction (up to 61%) of aerobic ATP production was maintained during prolonged (70 hr) anoxia (Zs.-Nagy & Ermini, 1972). From rates of oxygen consumption and rates of accumulation of fermentation products, a calculation suggested only 5% of aerobic ATP production was maintained during anoxia (dezwaan & Wijsman. 1976). Apart from differences in species and methods, a fundamental cause of such disagreements is that chemical inventory of a new steady state cannot reveal the actual rates of ATP synthesis and hydrolysis involved in reaching that state. Clearly needed is a non-destructive method of measuring total metabolism, continuously and independently of oxygen consumption. Measuring heat production has been suggested as a way to study the shifting balance between aerobic and anaerobic metabolism of marine invertebrates (Hammen, 1976). Others have noted the potential contribution of direct calorimetry to “better insight into the quantitative relationships of invertebrate anoxibiosis” (Gnaiger, 1977). The first adult marine invertebrate to have its metabolic rate measured by calorimetry was the gastropod Nucella lapillus, which had heat production of 955
0.08 cal/hr per mg N (Grainger, 1968). This is approximately equivalent to 3 J/hr per g tissue. The purpose was to compare calorimetry with respirometry. and the ratio of heat production to oxygen consumption was within the range expected for combustion of common food substances. The shore crab Carcinus mamas. was placed in a calorimeter to determine salinity effects on metabolism, while avoiding the complex responses sometimes shown by oxygen consumption data (Spaargaren. 1975). This animal produced heat at the rate of approx 1 J/hr per g total. Such results suggested that the rate of warming of 50-100 ml sea water in a Dewar flask by accumulated heat from small animals might be measurable by a mercury thermometer with expanded scale. The first results of such experiments are reported here. The hypothesis is that metabolic rates of marine molluscs are constant at a fixed temperature, and are the same whether measured by heat production or oxygen consumption. It follows that the ratio between the rates is also constant, and agrees closely with the ratio determined from combustion of food substances.
MATERIALS The
animals
AND
METHODS
used in this study
were collected 17 January to 24 April 1978 from the intertidal zone of Narragansett Bay, RI. In most cases, heat production was determined within 24 hr of collection. and oxygen consumption was determined the following day. The sea water temperature was S-8°C during this time, and the animals were kept in sea water from their habitat in a cold box at 10°C between experiments. Salinity was 27.9-32.1 oIXmexcept for oysters at salinity of 11.4”,,,. The numbers of animals used in each experiment were: five Crassosfrea: 10 Mvtilus: one Mya: one Mercenaria: 10 Littorina: one Libhia. After
metabolism measurements were completed, a number of the molluscs were dissected, and parts were weighed on an analytical balance to obtain relative fractions of shell, tissue, and fluid. Living tissue made up 10.2&23.48”,b of the total weight
in the various
species (Table
1).
C. S. HAMMEN
956 Table
I. Body proportions
Shell Tissue Fluid Total
2.109 I.053 I.918 5.080
of molluscs
41.28 20.56 38.16 100.00
used in metabolism
14.205 12.192 25.523 5 1.920
Lifrorina (2)
0
g
27.36 23.48 49.16 100.00
experiments
57.970 9.313 23.972 91.254
63.53 10.20 26.27
IOO.00
Cru.wosrrea (2, I,
E
(1 II
Shell Tissue Fluid
3.319 0.965 0.402
70.82 20.60 8.58
12.044 2.846 4.265
62.8X 14.86 _&... ,716
Total
4.686
100.00
19.155
100.00
The calorimeter was a simple, heat-retention type, consisting of two 475-ml Dewar flasks (“Thermos” brand) set in closely fitting insulated containers (“Polyfoam”) 40 mm thick. and closed with rubber stoppers through which were inserted mercury thermometers (ASTM 116C) graduated to 0.01 C from 18.9-25.1 C. The total weight of animals plus sea water in one flask was 50-14Og. and the matching flask contained an equal weight of sea water plus empty shells. Readings of temperature were taken on closing. and at IO- or 20-minute intervals up to 3 hr. The product of net temperature rise and weight of flask contents gave calories. from which joules were calculated. The apparatus was essentially the same as the “differential micro-calorimeter” of Hill (1911) and Davies (1966). but without electronics. Oxygen uptake was determined by standard manometric methods (Umbreit er al., 1972) on the constant-pressure. variable-volume principle. Mytilus and Lirtorina respiration rates were determined collectively and C’rassostrea rates individually.
the temperature inside both flasks increased durmg experiments. indicating net movement of heat from , surroundings to interior. Equilibration required 3G40min; then the temperature rise in the vessel with animals always exceeded that in the blank or control vessel (Fig. 1). The spider crab Libinicl dubia had a lower weight-specific heat production than the molluscs, 1.24 J/‘hr per g. but this was based on total body weight, not tissue alone. Oxygen consumption rates varied from 1.83 to 4.11 pmol/hr per g tissue in the various species. These are the maximum rates observed. The best experiment with Mytilus is shown in Fig. 1. Much lower rates were also seen, sometimes approaching zero. Four of the five oysters respired at extremely low rates.
RESULTS
Heat was produced tissue by the various Table
at rates of 1.24-6.23 J/hr per g species (Table 2). In all cases.
2. Metabolic
DISCUSSION
These experiments demonstrate that heat production of marine bivalve molluscs is measurable with a simple. heat-retention, differential calorimeter. When a minimum weight of about log living tissue
rates of marine molluscs and a crustacean. metry and by manometry
determined
by calori-
mean wt (g)
temperature
( C)
QH
QO
5.32
23.8
1.59
2.50
0.635
18.60
24.1
6.23
1.83
3.40
QH,Qo
Mollusca Pelecypoda Myfilus edulis Crassostrea rirginica Mya arrnaria
51.9
24.5
I .90
4.11
0.462
Mercenaria rnercenaria Gastropoda
91.6
71.0
3.08
2.68
1.15
4.14
21.8
1.62
3.73
0.434
8.41
24.4
I .24
2.61
0.477
Littorina lirtorea Crustaced Libiuia dubia
QH in J/hr per g wet. Q. in pmol/hr
per g wet. Temperatures
at start of calorimetry.
Metabolic
rates of marine
bivalve
molluscs
957
23.5--
1.0 --
ml
Fig. I. Upper curves: Heat production by 10 M~filus edulis, total 53.23 g. tissue 10.94 g. temperature at start 23.80 C. Circles: temperature in animal flask. Squares: temperature in blank flask. Experimental vessel contained animals plus 46.77 ml sea water: blank contained 55.7Og shells plus 44.30 ml sea water. salinity 3 I .4”‘& Result corresponds to a net heat production of I.59 J/hr per g tissue. Lower curve: Oxygen consumption by same 10 animals in 22 ml SW, salinity 30.5”<,. bath temperature 21.0 C. Maximum rate during last 40min corresponds to 0.66ml/hr or 2.50ltmol Ozhr per g tissue.
made up part of total flask contents of 100 g, the rate of temperature increase was 0.02-0.20”Chr greater than blank. corresponding to metabolic rates of 1.66.2 Jhr per g tissue. Rates in the same range were found for a gastropod and a crustacean, indicating that the method is applicable to other groups as well. Calorimetry has been carried out previously on four species of gastropods and three crustaceans (Table 3). No data on bivalves has been found. Total metabolic rates of the gastropods, calculated as 1.72-2.74 J/hr per g tissue, were all greater than our rate for Littorina, 1.62. However, our animals were collected and measured in mid-March, just before the end of winter, when their metabolism might be expected to be depressed. The Libinia rate, 1.24, agrees well with a published rate for the somewhat larger Carcinus, 1.05, while the two smaller crustaceans had greater rates. 2.23 and 8.64. Smaller animals are well known to have higher weight-specific metabolic rates. The parallel experiments on oxygen consumption of the same animals gave rates of 1.83-4.11 ~01 Or/hr per g tissue. Some very low rates, approaching
zero, were also observed. This is common in bivalves that close their valves tightly and cease to consume oxygen, even while it remains abundant in the medium. In the best experiment with 10 Myths. the majority of the animals apparently began aerobic respiration after 2 hr in the respirometer (Fig. 1). The rate found in this experiment, 2.50pmol/hr per g. is identical to the average rate in recent literature (de Zwaan & Wijsman, 1976). On the other hand. the maximum rate observed for Crassosrrra. I .83 pmol/hr per g tissue, is only about one-eighth of a calculated average of 13.83 pmol/hr per g tissue, determined by Galtsoff (1964, p. 207) for six fully-open oysters in a chamber with continuous flow of aerated sea water. a condition much closer to their natural environment. Oxygen consumption rates of Mercenaria vary with pumping rates, which were probably sub-maximal in our animal, confined to a small volume of sea water. The ratio of heat production to oxygen consumption QH/Qo is analogous and numerically equivalent to AH/A0 for combustion of food substances, when the same units are used. Extreme values are 0.432 J//*mol for complete oxidation of alanine and
c’. 8. HAMMES Table
3. Metabolic Mean wt lg)
rates of molluscs
and crustaceans
previously
reported
Temperature
( C)
Qo
QH~Q~
Reference
Mollusca Gastropoda Litiiriuetr p~‘rrycr
20.4
1.72*
7.43
0.244
.b Uct’llu /upllhc.\ (marine)
7.47
20.4
3.74*
6.15
0.440
Biotttphalari~ qlahrara
0.75
27.0
2.66
7.01
0.380
4
1.79
7.37
0.243
5
20.4
2.23
5.44
0.420
1
25.0
20.0
1.05
2
_~
25.0
8.64t
3
He/i\- pomurio (isolated hearts) Crustacea .Asrllu.~ uyuaticus (FW isopod) Curcini4.c maella.\ (marine crab) C~~clop.\ abjxsorum
0.107
(FW copepod) QE, in J/hr per g wet. Qri in pmol/hr per g wet. * Based on 1 mg N = 122 mg tissue. t Based on I mg dry = 5 mg tissue (80°0 water). References: (1) Grainger (1968). (2) Spaargaren (1975). (31 Lamprecht (1977). (5) Herold (19775.
for glutamic acid. with 0.470 for glucose (Cramer, 1968). In these experiments, one species of bivalve mollusc. Mru Llrenariu, the gastropod Litrorinu, and the decapod crustacian Libinia yielded ratios in this range. The other three bivalves gave larger values. indicating that total metabolism measured as heat production was greater than total metabolism as oxygen consumption. Especially noteworthy was the large discrepancy between measurements on Crassosfrea, in which oxygen consumption greatly underestimated total metabolic rate. When the Q. cited above for Crassosrrca is used, the ratio becomes 0.450J/~mol. suggesting that our QH, exceeding that of the other five species, is correct. In no case was oxygen uptake greater than the equivalent heat production in these six species. In the literature (Table 3), the isopod Asellus and the marine gastropod Nucella had ratios, 0.420 and 0.440. in the correct range, while three other snails had oxygen consumption exceeding heat production. Such results may be due to temporarily high Q. after a period of oxygen debt, or possibly some loss of heat due to evaporation. Animal calorimetry has been employed sporadically since Lavoisier & Laplace (I 780) showed that the respiration of a guinea pig is, in several respects, very similar to combustion of carbon. The development of a highly sensitive instrument, the Tian-Calvet microcalorimeter, based on the heat-flux principle, has permitted measurements of metabolic rate on animals as small as a single Drosophila (Prat. 1969). This type of instrument was used to verify a constant relation between heat output and oxygen consumption in Tenebrio pupae (Peakin, 1973). A similar instrument was used to show that anaerobic metabolism, 0.3Xx
(1976). (4) Becker & Lamprecht
presumably of micro-organisms. in organically-rich sediments may greatly exceed aerobic metabolism (Pamatmat & Bhagwat, 1973). Until now, however, the potential of calorimetry for studies of total metabolism of invertebrates other than insects has not been exploited. The problem of energy production and utilization in species that com.monly enter anaerobic states is an especially attractive field for research. Heat production depends primarily on rates of ATP hydrolysis, which in turn depend on basic cellular work, such as maintenance of concentration differences across membranes, ciliary activity. heart beat, etc. Rates of ATP synthesis must equal rates of hydrolysis when a steady state is maintained. However, the dependence on oxygen consumption is not close: because capture of the bond energy of glucose in ATP may be just as efficient in anaerobic succinate formation as in aerobic electron transport (Gnaiger. 1977). Thus, while supplies of glycogen are abundant, as they are in bivalve mollusts, there is no need for cellular work or heat production to diminish in anoxia. Future work should be devoted to measuring heat production and oxygen consumption concomitantly. and to following total metabolism from aerobic through transition to the totally anoxic state.
REFERENCES
BECKER W. & LAMPRECHT 1. (1977) Mikrokalorimetrische Untersuchungen zum Wirt-Parasit-Verhlltnis zwischen Biomphalaria glabrata asitenk. 53, 297-305.
und
Schistosoma
mansoni.
2. Par-
DAVIES P. M. C. (1966) The energy relations of Carassius auratus L. II. The effect of food, crowding and darkness
Metabolic
rates of marine
on heat production. Camp. Biochem. Physiol. 17, 983-995. ELLINGTON W. R. & HAMMEN C. S. (1977) Metabolic compensation to reduced oxygen tensions in the sea cucumber, Sclerodacryla briareus. J. camp. Ph.rsiof. 122, 347-358. GALTSOFF P. S. (1964) The American oyster Crassosrrea airginica Gmehn. Fish. Bull. 64. GNAIGER E. (1977) Thermodynamic considerations of invertebrate anoxibiosis. Applications of Calorimetry in L&J Sciences (Edited by LAMPRECHT I. & SCHAARSCHMIDT B.). pp. 281-303. Walter de Gruyter. Berlin. GRAINGER J. N. R. (1968) The relation between heat production. oxygen consumption and temperature in some poikilotherms. In Quantitatioe Biology of Merabolisnt (Edited by LOCKER A.). pp. 86-89. Springer-Verlag. New York. HAMMEN C. S. (1976) Respiratory adaptations: invertebrates. In Estuarine Processes (Edited by WILEY M. L.), Vol. I. pp. 347-355. Academic Press, New York. HEROLD J. P. (1977) Advantage of microcalorimetric investigations in cardiac energetic physiology: determination of oxidative efficiency in the isolated snail heart. Comp. Biochem. PhJsiol. 58A, 251-254. HILL A. V. (1911) The total energy exchanges of intact cold-blooded animals at rest. 1. Physiol., Land. 43, 379-394. LAMPRECHT 1. (1976) Application of calorimetry to the evaluation of metabolic data for whole organisms. Biothem. Sot. Trans. 4, 565-569.
bivalve
molluscs
959
LAVOISIERA. & LAPLACE P. (I 780) Memoire sur la chaleur. Mhm. Acad. Sci.. Paris. In Great Experiments in Biolog) (1955). (Edited by GABRIEL M. L. and FOCEL S.). Prentice-Hall. Englewood Cliffs. PAMATMAT M. M. & BHAGWAT A. M. (1973) Anaerobic metabolism ,in Lake Washington sediments. Limnol. Oceanogr.
18, 611-627.
PEAKIN G. J. (1973) The measurement of the costs of maintenance in terrestrial poikilotherms: a comparison between respirometry and calorimetry. Esperienria 29, 801-802.
PRAT H. (1969) Calorimetry of higher organisms. In Biochemical Microcalorimetry (Edited by BROWN H. D.). pp. 181-198. Academic Press, New York. SPAARGAREN D. H. (1975) Heat production of the shorecrab Carcinus maenas L. and its relation to osmotic stress. Proc. 9rh Europ. Mar. Biol. Symp. Aberdeen. (Edited by BARNES H.), pp. 4755482. University Press, Scotland. UMBREIT W. W., BURRIS R. H. & STAUFFER J. F. (1972) Manometric and Biochemical Techniques. 5th Edition, Burgess. Minneapolis. ZS-NAGY I. & ERMINI M. (1972) ATP production in the tissues of the bivalve Myrilus galloprocincialis (Pelecypoda) under normal and anoxic conditions. Comp. Biothem. Physiol. 43B, 593-600. DEZWAAN A. & WIJSMAN T. C. M. (1976) Anaerobic metabolism in Bivalvia (Mollusca). Comp. Biochem. Physiol. 54B, 3 13-324.
RATES OF MARINE BIVALVE DETERMINED BY CALORIMETRY
MOLLUSCS
C. S. HAMMEN University
of Rhode
Island.
(Rewired
Kingston.
R102881.
U.S.A
19 June 1978)
Abstract-l. Rates of heat production (QH) of four species of marine bivalve molluscs. a gastropod. and a decapod crustacean were determined with a heat-retention. differential calorimeter. 2. Rates of oxygen consumption (Qo) of the same animals were determined by standard manometric methods. 3. QH varied with species from 1.6 to 6.2 J/hr per g tissue. and Q. from 1.8 to 4.1 pmol/hr per g. 4. The bivalve MW urmariu. the gastropod Littorinu litrorru, and the decapod Lihiu duhiu had ratios of QH/Qo equal to 0.462. 0.434. and 0.477. respectively. which agree closely with the ratios of AH/A0 for combustion of common food substances. 5. The ratios Q,,/Qo for Mytilus edulis. Mrrcwuric~ rwrcmuria. and Crmsostwtr kyinica were 0.635. 1.15. and 3.40. respectively. which indicate Q. was too low to represent accurately the total metabolism of these species.
INTRODUCTION
Direct calorimetry has been used very little as a measure of metabolism of marine invertebrates because of the greater convenience and sensitivity of oxygen-consumption methods. However, many animals not only tolerate but normally enter anaerobic states, during which rates of oxygen uptake are near zero (Hammen. 1976). The conversion of labelled substrates into other substances indicates that intermediary metabolism continues unabated in many species during early phases of anoxia (Ellington & Hammen. 1977). Aerobic and anaerobic metabolic rates of marine mussels of the genus Mjtilus have been compared by two methods. From tissue concentrations of ATP and related nucleotides, a high fraction (up to 61%) of aerobic ATP production was maintained during prolonged (70 hr) anoxia (Zs.-Nagy & Ermini, 1972). From rates of oxygen consumption and rates of accumulation of fermentation products, a calculation suggested only 5% of aerobic ATP production was maintained during anoxia (dezwaan & Wijsman. 1976). Apart from differences in species and methods, a fundamental cause of such disagreements is that chemical inventory of a new steady state cannot reveal the actual rates of ATP synthesis and hydrolysis involved in reaching that state. Clearly needed is a non-destructive method of measuring total metabolism, continuously and independently of oxygen consumption. Measuring heat production has been suggested as a way to study the shifting balance between aerobic and anaerobic metabolism of marine invertebrates (Hammen, 1976). Others have noted the potential contribution of direct calorimetry to “better insight into the quantitative relationships of invertebrate anoxibiosis” (Gnaiger, 1977). The first adult marine invertebrate to have its metabolic rate measured by calorimetry was the gastropod Nucella lapillus, which had heat production of 955
0.08 cal/hr per mg N (Grainger, 1968). This is approximately equivalent to 3 J/hr per g tissue. The purpose was to compare calorimetry with respirometry. and the ratio of heat production to oxygen consumption was within the range expected for combustion of common food substances. The shore crab Carcinus mamas. was placed in a calorimeter to determine salinity effects on metabolism, while avoiding the complex responses sometimes shown by oxygen consumption data (Spaargaren. 1975). This animal produced heat at the rate of approx 1 J/hr per g total. Such results suggested that the rate of warming of 50-100 ml sea water in a Dewar flask by accumulated heat from small animals might be measurable by a mercury thermometer with expanded scale. The first results of such experiments are reported here. The hypothesis is that metabolic rates of marine molluscs are constant at a fixed temperature, and are the same whether measured by heat production or oxygen consumption. It follows that the ratio between the rates is also constant, and agrees closely with the ratio determined from combustion of food substances.
MATERIALS The
animals
AND
METHODS
used in this study
were collected 17 January to 24 April 1978 from the intertidal zone of Narragansett Bay, RI. In most cases, heat production was determined within 24 hr of collection. and oxygen consumption was determined the following day. The sea water temperature was S-8°C during this time, and the animals were kept in sea water from their habitat in a cold box at 10°C between experiments. Salinity was 27.9-32.1 oIXmexcept for oysters at salinity of 11.4”,,,. The numbers of animals used in each experiment were: five Crassosfrea: 10 Mvtilus: one Mya: one Mercenaria: 10 Littorina: one Libhia. After
metabolism measurements were completed, a number of the molluscs were dissected, and parts were weighed on an analytical balance to obtain relative fractions of shell, tissue, and fluid. Living tissue made up 10.2&23.48”,b of the total weight
in the various
species (Table
1).
C. S. HAMMEN
956 Table
I. Body proportions
Shell Tissue Fluid Total
2.109 I.053 I.918 5.080
of molluscs
41.28 20.56 38.16 100.00
used in metabolism
14.205 12.192 25.523 5 1.920
Lifrorina (2)
0
g
27.36 23.48 49.16 100.00
experiments
57.970 9.313 23.972 91.254
63.53 10.20 26.27
IOO.00
Cru.wosrrea (2, I,
E
(1 II
Shell Tissue Fluid
3.319 0.965 0.402
70.82 20.60 8.58
12.044 2.846 4.265
62.8X 14.86 _&... ,716
Total
4.686
100.00
19.155
100.00
The calorimeter was a simple, heat-retention type, consisting of two 475-ml Dewar flasks (“Thermos” brand) set in closely fitting insulated containers (“Polyfoam”) 40 mm thick. and closed with rubber stoppers through which were inserted mercury thermometers (ASTM 116C) graduated to 0.01 C from 18.9-25.1 C. The total weight of animals plus sea water in one flask was 50-14Og. and the matching flask contained an equal weight of sea water plus empty shells. Readings of temperature were taken on closing. and at IO- or 20-minute intervals up to 3 hr. The product of net temperature rise and weight of flask contents gave calories. from which joules were calculated. The apparatus was essentially the same as the “differential micro-calorimeter” of Hill (1911) and Davies (1966). but without electronics. Oxygen uptake was determined by standard manometric methods (Umbreit er al., 1972) on the constant-pressure. variable-volume principle. Mytilus and Lirtorina respiration rates were determined collectively and C’rassostrea rates individually.
the temperature inside both flasks increased durmg experiments. indicating net movement of heat from , surroundings to interior. Equilibration required 3G40min; then the temperature rise in the vessel with animals always exceeded that in the blank or control vessel (Fig. 1). The spider crab Libinicl dubia had a lower weight-specific heat production than the molluscs, 1.24 J/‘hr per g. but this was based on total body weight, not tissue alone. Oxygen consumption rates varied from 1.83 to 4.11 pmol/hr per g tissue in the various species. These are the maximum rates observed. The best experiment with Mytilus is shown in Fig. 1. Much lower rates were also seen, sometimes approaching zero. Four of the five oysters respired at extremely low rates.
RESULTS
Heat was produced tissue by the various Table
at rates of 1.24-6.23 J/hr per g species (Table 2). In all cases.
2. Metabolic
DISCUSSION
These experiments demonstrate that heat production of marine bivalve molluscs is measurable with a simple. heat-retention, differential calorimeter. When a minimum weight of about log living tissue
rates of marine molluscs and a crustacean. metry and by manometry
determined
by calori-
mean wt (g)
temperature
( C)
QH
QO
5.32
23.8
1.59
2.50
0.635
18.60
24.1
6.23
1.83
3.40
QH,Qo
Mollusca Pelecypoda Myfilus edulis Crassostrea rirginica Mya arrnaria
51.9
24.5
I .90
4.11
0.462
Mercenaria rnercenaria Gastropoda
91.6
71.0
3.08
2.68
1.15
4.14
21.8
1.62
3.73
0.434
8.41
24.4
I .24
2.61
0.477
Littorina lirtorea Crustaced Libiuia dubia
QH in J/hr per g wet. Q. in pmol/hr
per g wet. Temperatures
at start of calorimetry.
Metabolic
rates of marine
bivalve
molluscs
957
23.5--
1.0 --
ml
Fig. I. Upper curves: Heat production by 10 M~filus edulis, total 53.23 g. tissue 10.94 g. temperature at start 23.80 C. Circles: temperature in animal flask. Squares: temperature in blank flask. Experimental vessel contained animals plus 46.77 ml sea water: blank contained 55.7Og shells plus 44.30 ml sea water. salinity 3 I .4”‘& Result corresponds to a net heat production of I.59 J/hr per g tissue. Lower curve: Oxygen consumption by same 10 animals in 22 ml SW, salinity 30.5”<,. bath temperature 21.0 C. Maximum rate during last 40min corresponds to 0.66ml/hr or 2.50ltmol Ozhr per g tissue.
made up part of total flask contents of 100 g, the rate of temperature increase was 0.02-0.20”Chr greater than blank. corresponding to metabolic rates of 1.66.2 Jhr per g tissue. Rates in the same range were found for a gastropod and a crustacean, indicating that the method is applicable to other groups as well. Calorimetry has been carried out previously on four species of gastropods and three crustaceans (Table 3). No data on bivalves has been found. Total metabolic rates of the gastropods, calculated as 1.72-2.74 J/hr per g tissue, were all greater than our rate for Littorina, 1.62. However, our animals were collected and measured in mid-March, just before the end of winter, when their metabolism might be expected to be depressed. The Libinia rate, 1.24, agrees well with a published rate for the somewhat larger Carcinus, 1.05, while the two smaller crustaceans had greater rates. 2.23 and 8.64. Smaller animals are well known to have higher weight-specific metabolic rates. The parallel experiments on oxygen consumption of the same animals gave rates of 1.83-4.11 ~01 Or/hr per g tissue. Some very low rates, approaching
zero, were also observed. This is common in bivalves that close their valves tightly and cease to consume oxygen, even while it remains abundant in the medium. In the best experiment with 10 Myths. the majority of the animals apparently began aerobic respiration after 2 hr in the respirometer (Fig. 1). The rate found in this experiment, 2.50pmol/hr per g. is identical to the average rate in recent literature (de Zwaan & Wijsman, 1976). On the other hand. the maximum rate observed for Crassosrrra. I .83 pmol/hr per g tissue, is only about one-eighth of a calculated average of 13.83 pmol/hr per g tissue, determined by Galtsoff (1964, p. 207) for six fully-open oysters in a chamber with continuous flow of aerated sea water. a condition much closer to their natural environment. Oxygen consumption rates of Mercenaria vary with pumping rates, which were probably sub-maximal in our animal, confined to a small volume of sea water. The ratio of heat production to oxygen consumption QH/Qo is analogous and numerically equivalent to AH/A0 for combustion of food substances, when the same units are used. Extreme values are 0.432 J//*mol for complete oxidation of alanine and
c’. 8. HAMMES Table
3. Metabolic Mean wt lg)
rates of molluscs
and crustaceans
previously
reported
Temperature
( C)
Qo
QH~Q~
Reference
Mollusca Gastropoda Litiiriuetr p~‘rrycr
20.4
1.72*
7.43
0.244
.b Uct’llu /upllhc.\ (marine)
7.47
20.4
3.74*
6.15
0.440
Biotttphalari~ qlahrara
0.75
27.0
2.66
7.01
0.380
4
1.79
7.37
0.243
5
20.4
2.23
5.44
0.420
1
25.0
20.0
1.05
2
_~
25.0
8.64t
3
He/i\- pomurio (isolated hearts) Crustacea .Asrllu.~ uyuaticus (FW isopod) Curcini4.c maella.\ (marine crab) C~~clop.\ abjxsorum
0.107
(FW copepod) QE, in J/hr per g wet. Qri in pmol/hr per g wet. * Based on 1 mg N = 122 mg tissue. t Based on I mg dry = 5 mg tissue (80°0 water). References: (1) Grainger (1968). (2) Spaargaren (1975). (31 Lamprecht (1977). (5) Herold (19775.
for glutamic acid. with 0.470 for glucose (Cramer, 1968). In these experiments, one species of bivalve mollusc. Mru Llrenariu, the gastropod Litrorinu, and the decapod crustacian Libinia yielded ratios in this range. The other three bivalves gave larger values. indicating that total metabolism measured as heat production was greater than total metabolism as oxygen consumption. Especially noteworthy was the large discrepancy between measurements on Crassosfrea, in which oxygen consumption greatly underestimated total metabolic rate. When the Q. cited above for Crassosrrca is used, the ratio becomes 0.450J/~mol. suggesting that our QH, exceeding that of the other five species, is correct. In no case was oxygen uptake greater than the equivalent heat production in these six species. In the literature (Table 3), the isopod Asellus and the marine gastropod Nucella had ratios, 0.420 and 0.440. in the correct range, while three other snails had oxygen consumption exceeding heat production. Such results may be due to temporarily high Q. after a period of oxygen debt, or possibly some loss of heat due to evaporation. Animal calorimetry has been employed sporadically since Lavoisier & Laplace (I 780) showed that the respiration of a guinea pig is, in several respects, very similar to combustion of carbon. The development of a highly sensitive instrument, the Tian-Calvet microcalorimeter, based on the heat-flux principle, has permitted measurements of metabolic rate on animals as small as a single Drosophila (Prat. 1969). This type of instrument was used to verify a constant relation between heat output and oxygen consumption in Tenebrio pupae (Peakin, 1973). A similar instrument was used to show that anaerobic metabolism, 0.3Xx
(1976). (4) Becker & Lamprecht
presumably of micro-organisms. in organically-rich sediments may greatly exceed aerobic metabolism (Pamatmat & Bhagwat, 1973). Until now, however, the potential of calorimetry for studies of total metabolism of invertebrates other than insects has not been exploited. The problem of energy production and utilization in species that com.monly enter anaerobic states is an especially attractive field for research. Heat production depends primarily on rates of ATP hydrolysis, which in turn depend on basic cellular work, such as maintenance of concentration differences across membranes, ciliary activity. heart beat, etc. Rates of ATP synthesis must equal rates of hydrolysis when a steady state is maintained. However, the dependence on oxygen consumption is not close: because capture of the bond energy of glucose in ATP may be just as efficient in anaerobic succinate formation as in aerobic electron transport (Gnaiger. 1977). Thus, while supplies of glycogen are abundant, as they are in bivalve mollusts, there is no need for cellular work or heat production to diminish in anoxia. Future work should be devoted to measuring heat production and oxygen consumption concomitantly. and to following total metabolism from aerobic through transition to the totally anoxic state.
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und
Schistosoma
mansoni.
2. Par-
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rates of marine
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bivalve
molluscs
959
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