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Effect of body size, starvation, temperature and oxygen tension on the oxygen consumption of hatchery-reared ormers Haliotis tuberculata L.
Aquaculture, 56 (1986) 229-237 Elsevier Science Publishers B.V., Amsterdam
229 -
Printed
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Effect of Body Size, Starvation, Temperature and Oxygen Tension on the Oxygen Consumption of Hatchery-Reared Ormers Hdiotis tubercukzta L. G. GATY’,” and J.H. WILSON2.4 ‘U.E.R. des Sciences de la Vie, Laboratoire de Zoologie, Universitd de Caen (France) “Shellfish Research Laboratory, Department of Zoology, University College of Galway, Carna, Co. Galway (Ireland) “Present address: 45 Avenue Jeanne d’Arc, 5100 Chalons sur Marne (France) 4To whom reprint requests should be addressed (Accepted
13 June 1986)
ABSTRACT Gaty, G. and Wilson, J.H., 1986. Effect of body size, starvation, temperature and oxygen tension on the oxygen consumption of hatchery-reared ormers Haliotis tuberculata L. Aquaculture, 56: 229-237. The effects of body size, acclimation temperature, starvation and ambient oxygen tension on oxygen consumption rate and metabolic rate of the European abalone or ormer, Haliotis tuberculata L., were examined. An exponential relation was observed between dry tissue weight and oxygen consumption rate which varied with acclimation temperature and ration. The relation between standard oxygen consumption rate, tissue weight and acclimation temperature following a 14-day acclimation period for H. tuberculatu was VO2 .O. 06228.
W9.869.To.639
where VO, is oxygen consumption rate in ml 0, h-’ and W is dry tissue weight in g. Ormers exposed to declining oxygen tensions at 16” C showed little ability to regulate oxygen consumption rate. Oxygen dependence was highest in small starved ormers and lowest in large fed individuals.
INTRODUCTION
The ormer, Hal&s tuberculatu L., is the sole representative of the family Haliotidae or abalones in North Western Europe. It is indigenous to the Channel Islands and the Atlantic coast of France, and has been introduced recently into Ireland with a view to commercial farming. Juvenile ormers for ongrowing trials have now been produced on a regular basis in the Shellfish Research Laboratory (SRL) hatchery at Carna, Co. Galway, for several years. Ormers are known to prefer exposed rocky habitats, living from extreme low spring-
OO44-8486/86/$03.50
0 1986 Elsevier Science Publishers
B.V.
230
tide level down to 13 m where ambient oxygen tensions are high (Forster, 1962). Stephenson (1942) recorded high mortalities after 24 h in unaerated seawater. Successful intensive rearing of ormers in the SRL nursery and ongrowing systems has also been found to require vigorous water circulation and aeration (R. La Touche, personal communication, 1983). The objective of the present investigation was to measure oxygen consumption rates of hatchery-produced juvenile H. tuberculutu in relation to body weight, ration, holding temperature and ambient oxygen tension in order to establish oxygen requirements of ormers at the hatchery and nursery stages. The effects of body size and in some cases temperature have been studied in several of the Haliotidae. Sagara and Araki (1971) examined the acute response of oxygen consumption with ambient temperature for juvenile H, giguntea Gmelin and H. discus Reeve, while Uki and Kikuchi (1975) determined oxygen consumption in relation to size and acute temperature changes for juvenile and adult H. discus hunnui Ino. Apart from a brief mention by Montuori (1913) in a review of respiration in marine animals there is no similar information for H. tuberculutu. MATERIALS AND METHODS
Experiments were performed during June-September 1983 and 1984. Specimens of Huliotis tubercukztu weighed from 0.017 to 1.72 g dry tissue weight (approximately lo-50 mm shell length), a size range in excess of 1:50 as recommended by Kruger (1960) for accurate oxygen consumption estimates in relation to size. All animals were reared in hatcheries of the Shellfish Research Laboratory, Co. Galway. Oxygen consumption was measured using an E5046 Radiometer oxygen electrode connected to a Radiometer Analyser according to the method described by Crisp et al. (1978). The internal volume of the experimental chamber was 306 ml. Seawater (33-35 p.p.t.) used in experiments was filtered to remove particles > 2 pm in diameter The chamber was illuminated during experiments (450 lux) , which were carried out between 2.00 and 4.00 p.m to coincide with a 12-h illuminated period when the ormers were immobile. Oxygen consumption rates thus measured for starved ormers were assumed to represent standard rates, while oxygen consumption rates of fed ormers held at 16’ C represented fed rates. Ormers were removed after each experiment, blotted dry and weighed. Dry tissue weights were calculated from linear regressions of total wet weight on dry tissue weight to avoid sacrifice of experimental animals. Total wet weight (tot. wet wt. ) , total freeze-dried weight (tot. dry wt. ) , freeze-dried tissue weight (dry tiss. wt.) and freeze-dried shell weight (dry shell wt. ) were determined for 39 individuals from 0.X3-12.56 g total wet weight. Linear regressions relating these weights expressed as g gave the equations
231
Tot. dry wet. = 0.440. tot. wet wt.0.gg4 ( r = 0.999; P < 0.001) Dry tiss. wet. = 0.138. tot. wet wt.O.ggO( r = 0.999; P < 0.001) Dry shell wt. = 0.301. tot. wet wt.0.gg5 (r= 0.999; P < 0.001) where r = the correlation
coefficient.
Oxygen consumption in relation to size, temperature and nutrition Determinations were made at 8, 16 and 24’ C for three batches of temperature-acclimated ormers held without food for 2 weeks. A fourth batch held at 4 nC suffered a 100% mortality during the acclimation period. A fifth batch of ormers was held at 16°C for 2 weeks prior to determinations and fed Ulna lactuca L. to excess. All batches were subjected to 12-h periods of artificial light (6.00a.m.-6.00p.m.) anddark (6.00p.m.-6.00a.m.) duringtheholdingperiod. Four size ranges of ormers of lo-15 mm, 20-25 mm, 30-35 mm and 50-70 mm shell length comprised each batch. Oxygen consumption rates were measured for three different samples of each size range. Each sample consisted of 20, six, two or one individuals of the respective size ranges. Oxygen consumption in declining ambient oxygen tension Twelve experiments were carried out to examine the relation between oxygen consumption and oxygen tension. Ormers were allowed to exhaust the available oxygen in the respirometer chamber during experiments. This method simulated conditions which might prevail during holding in nursery tanks. Sassaman and Mangum (1972) concluded that accumulation of metabolites during such experiments is negligible. Two size ranges of ormers were used, namely, small specimens of 0.021? 0.003 g dry tissue weight and large specimens of 1.5120.13 g dry tissue weight. Oxygen consumption rates were measured for three different samples of 20 small ormers and two large ormers, respectively. Oxygen consumption rates during hypoxia for ormers fed on U. lactuca and after starvation for 2 weeks were measured for both size ranges. All experiments were conducted at 16” C. RESULTS
Oxygen consumption in relation to size, temperature and nutrition Oxygen consumption rates of Haliotis tuberculata of different sizes acclimated to temperatures of 8,16 and 24°C are shown in Table 1. The data have been fitted to the equation V02=aW”
232 TABLE 1 The relation between oxygen consumption rate ( VO,) and dry tissue weight ( W) ; linear regressions of log,, VO, (ml O2 h- ’ ) on log,, W (g) , where VO, = a- W*, n = number of determinations, r = correlation coefficient Experimental conditions
a
b
n
r
P
8°C 16°C 16°C 24°C
0.229 0.345 0.443 0.475
0.827 0.918 0.743 0.873
12 12 14 12
0.998 0.918 0.988 0.997
< 0.001
starved starved fed starved
where VO,=oxygen consumption rate in ml 0, h-l, W=dry tissue weight in g, and a and b are constants. It may be seen from Table 1 that mean oxygen consumption rate of individual ormers increased with tissue weight and temperature. The standard or starved oxygen consumption at 16” C increased from 0.042 ml 0, h-’ for a 0.10 g dry tissue weight ormer to 0.65 ml 0, h-’ for a 2.0 g dry tissue weight ormer. An ormer of 1.0 g dry tissue weight had standard oxygen consumption rates of 0.23,0.35 and 0.48 ml 0, h-’ at 8,16 and 24°C respectively. This is equivalent to QlO= 1.63 from 8 to 16” C and QID= 1.50 between 16 and 24’ C. Fed oxygen consumption rate was also higher than standard oxygen consumption rate in ormers of the same size at 16” C. The fed rate was 0.44 ml 0, h-’ as opposed to a standard rate of 0.33 ml O2 h- ’ for an ormer of 1.0 g dry tissue weight. Comparisons between regression coefficients (b) using Student’s t-test revealed significant differences between that at 8°C and 16°C ( t= 2.845; d.f. = 20; P< 0.01) . There was no significant difference, however, between b at 16°C and at 24°C (t=1.104; d.f. =20). The b values for standard and fed rates at 16 oC were significantly different ( t = 2.942; d.f. = 22; P < 0.01) . Multiple regression analysis of standard oxygen consumption rates for dry tissue weights and temperatures yields the equation VO, =0.06228.
W”.8”g - T0.“38
where VO, = standard oxygen consumption rate in ml 0, h- ‘, W= dry tissue weight in g, and T=temperature in “C. The multiple coefficient of determination, r*, is 0.9835 for 36 observations, signifying a high correlation of respiration rate with tissue weight and temperature [F (2,33) = 985.27; P < 0.0011, As V02 was recorded at only three temperatures, W contributed more significantly than T in the relation of VO, with T and W [F (1,33) = 74.951. Oxygen consumption in declining ambient oxygen tension Fig. 1 shows QO,, the mean weight specific oxygen consumption rates of fed and starved ormers of 0.021 g dry tissue weight and 1.51 g dry tissue weight at
233
1.1.
l.0.
09.
08. 07. Q02
06.
05
04.
03.
OQ-
0.1.
0’ 0
20
40
80
80
100
120
140
160
po2
Fig. 1. The effect of declining PO, (mm Hg) on 80, (ml 0, h- ’ g- ’ dry tissue weight) for fed and starved small ( 0.021 f 0.003 g dry tissue weight ) and large (1.51 k 0.13 g dry tissue weight ) ormers. Vertical bars represent k 1 standard deviation of the mean ( n = 3 ) .
16”C, respectively, in decreasing ambient oxygen tension. In all cases mean weight-specific oxygen consumption rates declined as oxygen tension fell, but slopes of the resultant curves varied for each experiment. Small ormers showed the steepest slope of the four curves, indicating a high degree of dependence of oxygen consumption rate on ambient oxygen tension. The lowest slope, that for large starved ormers, indicated greater oxygen independence. The ability to regulate oxygen consumption can be expressed quantitatively using the hyperbolic relation developed by Tang (1933 ) and Bayne (1973 ) to describe the relation between oxygen consumption rate and ambient oxygen tension
PO&O,
= K, + K2 -PO,
where PO,is the ambient oxygen tension (mm Hg) , QO, is the weight specific oxygen consumption (ml h-’ gg’ dry tissue weight) and K, and K2 are constants. The ratio of K1/K2 is an index of dependence of oxygen consumption rate on ambient oxygen tension (Bayne, 1971) . The larger the ratio the more oxygen consumption rate is dependent on ambient oxygen tension. The regression lines relating PO,/QO,and PO, and the values of ICI/K2 for the four
234 TABLE 2 Regressions of PO&O, on PO, giving the values of K1/KZ for starved and fed ormers of different sizes; r = correlation coefficient and n = number of determinations Dry tissue weight (g)
Nutritional state
n
K/K
r
0.021 0.021 1.51 1.51
Fed Starved Fed Starved
8 8 8 8
162.48 258.72 65.33 195.25
0.923 0.980 0.995 0.942
experiments are given in Table 2. Dependency decreased with size, but was much higher in starved ormers than in those that had been fed. DISCUSSION
Huliotis tuberuluta does not have an excessively
high oxygen consumption rate when compared with other gastropods. A fed ormer of 1.0 g dry tissue weight consumes 0.443 ml 0, h-l. Shumway (1981) cites values of a, the respiration rate per unit tissue weight, for live species grazing prosobranchs of similar tissue weight of 0.128-0.166 ml 0, h-l, while Bayne and Newell (1983) quote a mean value of a for 15 species grazing gastropods of 2.052 ? 1.25 ml 0, h-l. The latter authors suggest that this is a high value compared with sessile molluscs as it includes the high energetic costs of crawling. Newell and Pye (1971) found a high rate of oxygen consumption was related to crawling activity in Littorinu littoreu L. while low rates corresponded to phases of quiescence. Newell and Roy (1973) noted an increase of approximately 58% in oxygen consumption when L. littoreu became active. Uki and Kikuchi (1975 ) described relatively low amplitude circadian cycles in oxygen consumption of H. discus hunnui. Consumption increased slightly from dusk to midnight and decreased from midnight to midday as feeding activity decreased. The greatest increase in oxygen consumption recorded by Uki and Kikuchi was approximately 60% of the quiescent level. The restriction to movement imposed by the respiratory chamber prevents a true measure of oxygen consumption for active ormers, but even allowing for an energetic cost of activity of 60%, consumption would not exceed 0.8 ml 0, h-’ at most for an individual of 1.0 g dry tissue weight. Uki and Kikuchi (1975) formulated the respiratory response of H. discus hunnui to body weight and acute changes in temperature as VOZ*0.021* W0.8025.1.0963T where V02 = oxygen consumption rate in ml 0, h-l, and W= the total wet weight in g.
T the temperature
in ‘C,
In the present investigation the relationship between standard oxygen consumption rate, tissue weight and ambient temperature for H. tuberculata after acclimation was V02-0.06228.
W0.86g-T0.638
where VO, = oxygen consumption rate in ml 0, h- ‘, and W= dry tissue weight in g. The ormers used in the present study experienced exposure to air only occasionally during cleaning of the rearing units. Respiratory dependence tends to decrease in molluscs living in areas where there are higher risks of increased exposure to air and hypoxia. Murdoch and Shumway (1980) have shown that high-shore chitons have in general a high degree of oxygen independence compared to low-shore species which have little or no regulatory capacity. The high K1/& values recorded in the present study support the conclusion that the high level of respiratory dependence of this species may be associated with its sublittoral occurrence in exposed habitats in nature and continuous immersion in rearing tanks. In many species of mulluscs the primary route of oxygen uptake into superficial tissues has been shown to be direct, while oxygen supply to deeper tissues may be regulated by changes in cardiac activity or tissue utilisation. Booth and Mangum (1978) have demonstrated that cutting circulation in Modiolus demissus depressed oxygen consumption by only 14%. The blood of abalones has a low carrying capacity for oxygen of about 0.56-0.62% by volume ( Ainslie, 1980). Nakanishi (1978) has found that during hypoxia the heart rate of H. discus hannai was only 1.1 times faster at 45% saturation compared with the rate at 95lOO%, and declined at saturations below 30%. Constant cardiac output during hypoxia would not maintain a maximum oxygen diffusion gradient across the gills and therefore reduce the oxygen regulatory ability. Furthermore, the greater degree of respiratory independence of large ormers would suggest that larger individuals may be more resistant to short-term periods of hypoxia than smaller more oxygen dependent individuals as is found in chitons (Boyle, 1970). Several respiratory studies on molluscs have shown that increasing independence is correlated with increasing size (Bayne, 1971; Taylor and Brand, 1975; Shumway and Youngson, 1979; Mackay and Shumway, 1980; Murdoch and Shumway, 1980). Stephenson (1942) noted that small ormers of 9 mm shell length or less are only encountered below extreme low spring-tide level. Young H. discus hannai and H. siboldii live sublittorally in comparatively shallow water, and move into deeper water as they mature, only returning to shallows to spawn (Uno, 1967). It is doubtful, therefore, that oxygen consumption per se determines zonation of abalones. Physiological state also has a direct effect on respiratory regulation. The limited capacity of ormers to regulate oxygen consumption during environmental hypoxia has been shown to be reduced even further during starvation. Bayne (1971) found that
236
mussels lose to a large degree their oxygen independence changing from oxygen regulators to oxygen conformers.
during starvation,
ACKNOWLEDGEMENTS
We thank Mr. R. La Touche for the use of ormers in this study. Thanks are also due to Mr. I. Simons and Mr. D. Brown for technical assistance. This work was partly funded by the National Board for Science and Technology, Ireland. We also wish to thank Guinness Group Sales (Dublin) Ltd. for a kind donation of seawater cooling equipment.
REFERENCES Ainslie, B.L., 1980. The quantitative role of haemocyanin in the respiration of abalone (genus H&&is). J. Exp. Zool., 211: 87-99. Bayne, B.L., 1971. Oxygen consumption by three species of lamellibranch molluscs in declining ambient oxygen tension. Comp. Biochem. Physiol. A, 40: 955-970. Bayne, B.L., 1973. The responses of three species of bivalve molluscs to declining oxygen tension at reduced salinity. Comp. Biochem. Physiol. A, 45: 793806. Bayne, B.L. and Newell, R.C., 1983. Physiological energetics of marine molluscs. In: A.S.M. Saleuddin and K.L. Wilbur (Editors) The Mollusca. Academic Press, New York, Vol. 4 (1) : 407-515. Booth, C.E. and Mangum, C.P., 1978. Oxygen uptake and transport in the lamellibranch mollusc Modiolus demissus. Physiol. Zool., 51: 17-32. Boyle, P.R., 1970. Aspects of the ecology of a littoral chiton, S’ypharochitonpelliserpentis (Mollusca: Polyplacophora) . N.Z. J. Mar. Freshwater Res., 4: 364-384. Crisp, M., Davenport J. and Shumway, S.E., 1978. Effects of feeding and of chemical stimulation on the oxygen uptake of Nussarius reticulate (Gastropoda; Prosobranchia) . J. Mar. Biol. Assoc. U.K., 58: 387-399. Forster, G.R., 1962. Observations on the ormer population of Guernsey. J. Mar. Biol. Assoc. U.K., 42: 493-498. Kruger, F., 1960. Zur Frage der Grossenabhiingigkeit des Sauerstoffverbrauchs von Mytilus edulis L. Helgol. Wiss. Meeresunters., 7: 125-148. Mackay, J.E. and Shumway, S.E., 1980. Factors affecting oxygen consumption in the scallop Chlumys delicatula (Hutton). Ophelia, 19: 19-26. Montuori, A., 1913. Les processus oxydatifs chez les animaux marins en rapport avec la loi de superficie. Arch. Ital. Biol., 59: 213-234. Murdoch, R.C. and Shumway, S.E., 1980. Oxygen consumption in six species of chitons in relation to their position on the shore. Ophelia, 19: 127-144. Nakanishi, T., 1978. Studies on the effects of the environment on the heart rate of shellfishes. 2. The effects of temperature, low salinity and hypoxia on the heart rate of an abalone Haliotis (Nordotis) discus hannia Ino. Bull. Hokkaido Reg. Fish. Res. Lab., 43: 59-68. Newell, R.C. and Pye, V.I., 1971. Quantitative aspecte of the relationship between metabolism and temperature in the winkle, Littorina littorea (L.) . Comp. B&hem. Physiol. B, 38: 635-650. Newell, R.C. and Roy, A., 1973. A statistical model relating the oxygen consumption of a mollusk (Littorina littorea) to activity, body size and environmental conditions. Physiol. Zool., 46: 252-275.
237 Sagara, J. and Araki, K., 1971. Oxygen consumption of abalone in early developmental stage and juvenile. Bull. Tokai Reg. Fish. Lab., 65: 11-16. Sassaman, C. and Mangum, C.P., 1972. Adaptations to environmental oxygen levels in infaunal and epifaunal sea anemones. Biol. Bull. Mar. Biol. Lab., Woods Hole, 143: 657-678. Shumway, S.E., 1981. Factors affecting the oxygen consumption of the marine pulmonate Amphibola crenata. Biol. Bull. Mar. Biol. Lab., Woods Hole, 160: 332-347. Shumway, S.E. and Youngson, A., 1979. The effects of fluctuating salinity on the physiology of Modiolus demissw (Dillwyn). J. Exp. Mar. Biol. Ecol., 40: 167-181. Stephenson, T.A., 1942. Notes on Zfaliotis tubercuba. J. Mar. Biol. Assoc. U.K., 13: 480-495. Tang, P.S., 1933. On the rate of oxygen consumption by tissues and lower organisms as a function of oxygen tension. &. Rev. Biol., 8: 260-274. Taylor, A.C. and Brand, A.R., 1975. Effects of hypoxia and body size on the oxygen consumption of the bivalve Arctica islandica (L.). J. Exp. Mar. Biol. Ecol., 19: 187-196. Uki, N. and Kikuchi, S., 1975. Oxygen consumption of the abalone, Haliotis discus hannai, in relation to body size and temperature. Bull. Tokai Reg. Fish. Lab., 35: 73-84. Uno, Y., 1967. Discussion of fisheries culture of abalones. Koseisha Koseikaku, pp. 643-677.
229 -
Printed
in The Netherlands
Effect of Body Size, Starvation, Temperature and Oxygen Tension on the Oxygen Consumption of Hatchery-Reared Ormers Hdiotis tubercukzta L. G. GATY’,” and J.H. WILSON2.4 ‘U.E.R. des Sciences de la Vie, Laboratoire de Zoologie, Universitd de Caen (France) “Shellfish Research Laboratory, Department of Zoology, University College of Galway, Carna, Co. Galway (Ireland) “Present address: 45 Avenue Jeanne d’Arc, 5100 Chalons sur Marne (France) 4To whom reprint requests should be addressed (Accepted
13 June 1986)
ABSTRACT Gaty, G. and Wilson, J.H., 1986. Effect of body size, starvation, temperature and oxygen tension on the oxygen consumption of hatchery-reared ormers Haliotis tuberculata L. Aquaculture, 56: 229-237. The effects of body size, acclimation temperature, starvation and ambient oxygen tension on oxygen consumption rate and metabolic rate of the European abalone or ormer, Haliotis tuberculata L., were examined. An exponential relation was observed between dry tissue weight and oxygen consumption rate which varied with acclimation temperature and ration. The relation between standard oxygen consumption rate, tissue weight and acclimation temperature following a 14-day acclimation period for H. tuberculatu was VO2 .O. 06228.
W9.869.To.639
where VO, is oxygen consumption rate in ml 0, h-’ and W is dry tissue weight in g. Ormers exposed to declining oxygen tensions at 16” C showed little ability to regulate oxygen consumption rate. Oxygen dependence was highest in small starved ormers and lowest in large fed individuals.
INTRODUCTION
The ormer, Hal&s tuberculatu L., is the sole representative of the family Haliotidae or abalones in North Western Europe. It is indigenous to the Channel Islands and the Atlantic coast of France, and has been introduced recently into Ireland with a view to commercial farming. Juvenile ormers for ongrowing trials have now been produced on a regular basis in the Shellfish Research Laboratory (SRL) hatchery at Carna, Co. Galway, for several years. Ormers are known to prefer exposed rocky habitats, living from extreme low spring-
OO44-8486/86/$03.50
0 1986 Elsevier Science Publishers
B.V.
230
tide level down to 13 m where ambient oxygen tensions are high (Forster, 1962). Stephenson (1942) recorded high mortalities after 24 h in unaerated seawater. Successful intensive rearing of ormers in the SRL nursery and ongrowing systems has also been found to require vigorous water circulation and aeration (R. La Touche, personal communication, 1983). The objective of the present investigation was to measure oxygen consumption rates of hatchery-produced juvenile H. tuberculutu in relation to body weight, ration, holding temperature and ambient oxygen tension in order to establish oxygen requirements of ormers at the hatchery and nursery stages. The effects of body size and in some cases temperature have been studied in several of the Haliotidae. Sagara and Araki (1971) examined the acute response of oxygen consumption with ambient temperature for juvenile H, giguntea Gmelin and H. discus Reeve, while Uki and Kikuchi (1975) determined oxygen consumption in relation to size and acute temperature changes for juvenile and adult H. discus hunnui Ino. Apart from a brief mention by Montuori (1913) in a review of respiration in marine animals there is no similar information for H. tuberculutu. MATERIALS AND METHODS
Experiments were performed during June-September 1983 and 1984. Specimens of Huliotis tubercukztu weighed from 0.017 to 1.72 g dry tissue weight (approximately lo-50 mm shell length), a size range in excess of 1:50 as recommended by Kruger (1960) for accurate oxygen consumption estimates in relation to size. All animals were reared in hatcheries of the Shellfish Research Laboratory, Co. Galway. Oxygen consumption was measured using an E5046 Radiometer oxygen electrode connected to a Radiometer Analyser according to the method described by Crisp et al. (1978). The internal volume of the experimental chamber was 306 ml. Seawater (33-35 p.p.t.) used in experiments was filtered to remove particles > 2 pm in diameter The chamber was illuminated during experiments (450 lux) , which were carried out between 2.00 and 4.00 p.m to coincide with a 12-h illuminated period when the ormers were immobile. Oxygen consumption rates thus measured for starved ormers were assumed to represent standard rates, while oxygen consumption rates of fed ormers held at 16’ C represented fed rates. Ormers were removed after each experiment, blotted dry and weighed. Dry tissue weights were calculated from linear regressions of total wet weight on dry tissue weight to avoid sacrifice of experimental animals. Total wet weight (tot. wet wt. ) , total freeze-dried weight (tot. dry wt. ) , freeze-dried tissue weight (dry tiss. wt.) and freeze-dried shell weight (dry shell wt. ) were determined for 39 individuals from 0.X3-12.56 g total wet weight. Linear regressions relating these weights expressed as g gave the equations
231
Tot. dry wet. = 0.440. tot. wet wt.0.gg4 ( r = 0.999; P < 0.001) Dry tiss. wet. = 0.138. tot. wet wt.O.ggO( r = 0.999; P < 0.001) Dry shell wt. = 0.301. tot. wet wt.0.gg5 (r= 0.999; P < 0.001) where r = the correlation
coefficient.
Oxygen consumption in relation to size, temperature and nutrition Determinations were made at 8, 16 and 24’ C for three batches of temperature-acclimated ormers held without food for 2 weeks. A fourth batch held at 4 nC suffered a 100% mortality during the acclimation period. A fifth batch of ormers was held at 16°C for 2 weeks prior to determinations and fed Ulna lactuca L. to excess. All batches were subjected to 12-h periods of artificial light (6.00a.m.-6.00p.m.) anddark (6.00p.m.-6.00a.m.) duringtheholdingperiod. Four size ranges of ormers of lo-15 mm, 20-25 mm, 30-35 mm and 50-70 mm shell length comprised each batch. Oxygen consumption rates were measured for three different samples of each size range. Each sample consisted of 20, six, two or one individuals of the respective size ranges. Oxygen consumption in declining ambient oxygen tension Twelve experiments were carried out to examine the relation between oxygen consumption and oxygen tension. Ormers were allowed to exhaust the available oxygen in the respirometer chamber during experiments. This method simulated conditions which might prevail during holding in nursery tanks. Sassaman and Mangum (1972) concluded that accumulation of metabolites during such experiments is negligible. Two size ranges of ormers were used, namely, small specimens of 0.021? 0.003 g dry tissue weight and large specimens of 1.5120.13 g dry tissue weight. Oxygen consumption rates were measured for three different samples of 20 small ormers and two large ormers, respectively. Oxygen consumption rates during hypoxia for ormers fed on U. lactuca and after starvation for 2 weeks were measured for both size ranges. All experiments were conducted at 16” C. RESULTS
Oxygen consumption in relation to size, temperature and nutrition Oxygen consumption rates of Haliotis tuberculata of different sizes acclimated to temperatures of 8,16 and 24°C are shown in Table 1. The data have been fitted to the equation V02=aW”
232 TABLE 1 The relation between oxygen consumption rate ( VO,) and dry tissue weight ( W) ; linear regressions of log,, VO, (ml O2 h- ’ ) on log,, W (g) , where VO, = a- W*, n = number of determinations, r = correlation coefficient Experimental conditions
a
b
n
r
P
8°C 16°C 16°C 24°C
0.229 0.345 0.443 0.475
0.827 0.918 0.743 0.873
12 12 14 12
0.998 0.918 0.988 0.997
< 0.001
starved starved fed starved
where VO,=oxygen consumption rate in ml 0, h-l, W=dry tissue weight in g, and a and b are constants. It may be seen from Table 1 that mean oxygen consumption rate of individual ormers increased with tissue weight and temperature. The standard or starved oxygen consumption at 16” C increased from 0.042 ml 0, h-’ for a 0.10 g dry tissue weight ormer to 0.65 ml 0, h-’ for a 2.0 g dry tissue weight ormer. An ormer of 1.0 g dry tissue weight had standard oxygen consumption rates of 0.23,0.35 and 0.48 ml 0, h-’ at 8,16 and 24°C respectively. This is equivalent to QlO= 1.63 from 8 to 16” C and QID= 1.50 between 16 and 24’ C. Fed oxygen consumption rate was also higher than standard oxygen consumption rate in ormers of the same size at 16” C. The fed rate was 0.44 ml 0, h-’ as opposed to a standard rate of 0.33 ml O2 h- ’ for an ormer of 1.0 g dry tissue weight. Comparisons between regression coefficients (b) using Student’s t-test revealed significant differences between that at 8°C and 16°C ( t= 2.845; d.f. = 20; P< 0.01) . There was no significant difference, however, between b at 16°C and at 24°C (t=1.104; d.f. =20). The b values for standard and fed rates at 16 oC were significantly different ( t = 2.942; d.f. = 22; P < 0.01) . Multiple regression analysis of standard oxygen consumption rates for dry tissue weights and temperatures yields the equation VO, =0.06228.
W”.8”g - T0.“38
where VO, = standard oxygen consumption rate in ml 0, h- ‘, W= dry tissue weight in g, and T=temperature in “C. The multiple coefficient of determination, r*, is 0.9835 for 36 observations, signifying a high correlation of respiration rate with tissue weight and temperature [F (2,33) = 985.27; P < 0.0011, As V02 was recorded at only three temperatures, W contributed more significantly than T in the relation of VO, with T and W [F (1,33) = 74.951. Oxygen consumption in declining ambient oxygen tension Fig. 1 shows QO,, the mean weight specific oxygen consumption rates of fed and starved ormers of 0.021 g dry tissue weight and 1.51 g dry tissue weight at
233
1.1.
l.0.
09.
08. 07. Q02
06.
05
04.
03.
OQ-
0.1.
0’ 0
20
40
80
80
100
120
140
160
po2
Fig. 1. The effect of declining PO, (mm Hg) on 80, (ml 0, h- ’ g- ’ dry tissue weight) for fed and starved small ( 0.021 f 0.003 g dry tissue weight ) and large (1.51 k 0.13 g dry tissue weight ) ormers. Vertical bars represent k 1 standard deviation of the mean ( n = 3 ) .
16”C, respectively, in decreasing ambient oxygen tension. In all cases mean weight-specific oxygen consumption rates declined as oxygen tension fell, but slopes of the resultant curves varied for each experiment. Small ormers showed the steepest slope of the four curves, indicating a high degree of dependence of oxygen consumption rate on ambient oxygen tension. The lowest slope, that for large starved ormers, indicated greater oxygen independence. The ability to regulate oxygen consumption can be expressed quantitatively using the hyperbolic relation developed by Tang (1933 ) and Bayne (1973 ) to describe the relation between oxygen consumption rate and ambient oxygen tension
PO&O,
= K, + K2 -PO,
where PO,is the ambient oxygen tension (mm Hg) , QO, is the weight specific oxygen consumption (ml h-’ gg’ dry tissue weight) and K, and K2 are constants. The ratio of K1/K2 is an index of dependence of oxygen consumption rate on ambient oxygen tension (Bayne, 1971) . The larger the ratio the more oxygen consumption rate is dependent on ambient oxygen tension. The regression lines relating PO,/QO,and PO, and the values of ICI/K2 for the four
234 TABLE 2 Regressions of PO&O, on PO, giving the values of K1/KZ for starved and fed ormers of different sizes; r = correlation coefficient and n = number of determinations Dry tissue weight (g)
Nutritional state
n
K/K
r
0.021 0.021 1.51 1.51
Fed Starved Fed Starved
8 8 8 8
162.48 258.72 65.33 195.25
0.923 0.980 0.995 0.942
experiments are given in Table 2. Dependency decreased with size, but was much higher in starved ormers than in those that had been fed. DISCUSSION
Huliotis tuberuluta does not have an excessively
high oxygen consumption rate when compared with other gastropods. A fed ormer of 1.0 g dry tissue weight consumes 0.443 ml 0, h-l. Shumway (1981) cites values of a, the respiration rate per unit tissue weight, for live species grazing prosobranchs of similar tissue weight of 0.128-0.166 ml 0, h-l, while Bayne and Newell (1983) quote a mean value of a for 15 species grazing gastropods of 2.052 ? 1.25 ml 0, h-l. The latter authors suggest that this is a high value compared with sessile molluscs as it includes the high energetic costs of crawling. Newell and Pye (1971) found a high rate of oxygen consumption was related to crawling activity in Littorinu littoreu L. while low rates corresponded to phases of quiescence. Newell and Roy (1973) noted an increase of approximately 58% in oxygen consumption when L. littoreu became active. Uki and Kikuchi (1975 ) described relatively low amplitude circadian cycles in oxygen consumption of H. discus hunnui. Consumption increased slightly from dusk to midnight and decreased from midnight to midday as feeding activity decreased. The greatest increase in oxygen consumption recorded by Uki and Kikuchi was approximately 60% of the quiescent level. The restriction to movement imposed by the respiratory chamber prevents a true measure of oxygen consumption for active ormers, but even allowing for an energetic cost of activity of 60%, consumption would not exceed 0.8 ml 0, h-’ at most for an individual of 1.0 g dry tissue weight. Uki and Kikuchi (1975) formulated the respiratory response of H. discus hunnui to body weight and acute changes in temperature as VOZ*0.021* W0.8025.1.0963T where V02 = oxygen consumption rate in ml 0, h-l, and W= the total wet weight in g.
T the temperature
in ‘C,
In the present investigation the relationship between standard oxygen consumption rate, tissue weight and ambient temperature for H. tuberculata after acclimation was V02-0.06228.
W0.86g-T0.638
where VO, = oxygen consumption rate in ml 0, h- ‘, and W= dry tissue weight in g. The ormers used in the present study experienced exposure to air only occasionally during cleaning of the rearing units. Respiratory dependence tends to decrease in molluscs living in areas where there are higher risks of increased exposure to air and hypoxia. Murdoch and Shumway (1980) have shown that high-shore chitons have in general a high degree of oxygen independence compared to low-shore species which have little or no regulatory capacity. The high K1/& values recorded in the present study support the conclusion that the high level of respiratory dependence of this species may be associated with its sublittoral occurrence in exposed habitats in nature and continuous immersion in rearing tanks. In many species of mulluscs the primary route of oxygen uptake into superficial tissues has been shown to be direct, while oxygen supply to deeper tissues may be regulated by changes in cardiac activity or tissue utilisation. Booth and Mangum (1978) have demonstrated that cutting circulation in Modiolus demissus depressed oxygen consumption by only 14%. The blood of abalones has a low carrying capacity for oxygen of about 0.56-0.62% by volume ( Ainslie, 1980). Nakanishi (1978) has found that during hypoxia the heart rate of H. discus hannai was only 1.1 times faster at 45% saturation compared with the rate at 95lOO%, and declined at saturations below 30%. Constant cardiac output during hypoxia would not maintain a maximum oxygen diffusion gradient across the gills and therefore reduce the oxygen regulatory ability. Furthermore, the greater degree of respiratory independence of large ormers would suggest that larger individuals may be more resistant to short-term periods of hypoxia than smaller more oxygen dependent individuals as is found in chitons (Boyle, 1970). Several respiratory studies on molluscs have shown that increasing independence is correlated with increasing size (Bayne, 1971; Taylor and Brand, 1975; Shumway and Youngson, 1979; Mackay and Shumway, 1980; Murdoch and Shumway, 1980). Stephenson (1942) noted that small ormers of 9 mm shell length or less are only encountered below extreme low spring-tide level. Young H. discus hannai and H. siboldii live sublittorally in comparatively shallow water, and move into deeper water as they mature, only returning to shallows to spawn (Uno, 1967). It is doubtful, therefore, that oxygen consumption per se determines zonation of abalones. Physiological state also has a direct effect on respiratory regulation. The limited capacity of ormers to regulate oxygen consumption during environmental hypoxia has been shown to be reduced even further during starvation. Bayne (1971) found that
236
mussels lose to a large degree their oxygen independence changing from oxygen regulators to oxygen conformers.
during starvation,
ACKNOWLEDGEMENTS
We thank Mr. R. La Touche for the use of ormers in this study. Thanks are also due to Mr. I. Simons and Mr. D. Brown for technical assistance. This work was partly funded by the National Board for Science and Technology, Ireland. We also wish to thank Guinness Group Sales (Dublin) Ltd. for a kind donation of seawater cooling equipment.
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