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Effects of temperature and salinity on the metabolism and byssal formation of Brachidontes variabilis Krauss (Bivalvia)
Comp. Biochem. Physiol., 1978, Vol. 59A, pp. 101 to 105. Pergamon Press. Printed in Great Britain
EFFECTS OF TEMPERATURE A N D SALINITY ON THE METABOLISM A N D BYSSAL FORMATION OF BRACHIDONTES VARIABILIS KRAUSS (BIVALVIA) S. STERN and Y. ACHXTUV* Department of Zoology, The Hebrew University of Jerusalem, Jerusalem, Israel
(Received 22 March 1977) Al~traet--The effects of temperature and salinity on Brachidontes variabilis were studied. Increase in temperature from 27 to 33°C resulted in a net decrease in oxygen uptake. Salinity increments from 47 to 5 8 ~ resulted in a decrease in oxygen uptake with an apparent stabilization indicating adaptation. Combined increases in temperature and salinity resulted in initial fluctuations in oxygen uptake (either overshoot or undershoot), followed by a return to the pretest rate of oxygen uptake. 2. Nitrogen excretion increased in most of the experiments indicating enhanced utilization of proteins. Correlation was found between byssal formation (percentage of animals forming byssus) and the degree of stress imposed on the animals. 3. Mortality and survival were modified by the salinity regime imposed. Thermal tolerance significantly increased in high salinities. It is suggested that the osmoconforming ability of B. variabilis is responsible for such a relationship. 4. The metabolic plasticity of B. variabilis as expressed in this study is believed to have played a major role in its ability to migrate into the Mediterranean Sea.
INTRODUCTION Temperature and salinity are important environmental factors affecting the distribution of a wide range of marine organisms. The intertidal zone in particular is subjected to wide temperature and salinity fluctuations. The effects of temperature and salinity on intertidal organisms are reviewed by Kinne (1963, 1964a, b, 1971a, b). The mechanisms essential for life in the intertidal zone are summed up by Vernberg & Vernberg (1972~ Along the Sinai Peninsula there are a number of lagoons and other water bodies where temperature and salinity fluctuations are outstanding (Por, 1972). One of the most common animals there, the bivalve mollusc Brachidontes variabilis Krauss, is categorized as belonging to a marine assemblage of hyperhaline organisms (Por, 1972). With the opening of the Suez Canal, the Mediterranean and Red Sea came into direct c o n t a c t and this gave rise to faunal migrations. Brachidontes variabilis, a Red Sea species, has now reached the eastern Mediterranean (Barash & Danin, 1972). By evaluating some of the ecophysiological characteristics of Brachidontes variabilis, some insight may be gained as to the nature by which B. variabilis was successful in migrating into the Mediterranean Sea. The laboratory experiments involved studies on oxygen uptake, nitrogen excretion and byssal formation, with the view of determining the role of temperature and salinity in the ecology of Brachidontes variabilis.
Sea). All specimens selected were of size 23-26 mm. (maximum length of the shell)~ Experiments were carried out in Jerusalem in aquaria of 501. capacity with re-circulating seawater. Animals were not fed artificially, nor was the water in each aquarium passed through a selective filter. Prior to each experiment, all animals were acclimated to 21°C and 42%o for at least 2 weeks. Salinities were monitored by a Beckman Salinometer model RS-7B. Temperatures in the aquaria were maintained by an immersed heating element to a precision of +I°C. Eight experimental regimes were tested with eight animals in each experiment. Eight additional animals were transferred to each aquarium for reserve purposes. Oxygen uptake was determined by a Davies constant pressure respirometer (Davies, 1966). Animals were equilibrated for 1 hr prior to each reading of oxygen uptake. With the completion of the equilibration period, oxygen uptake was recorded in 15 rain intervals over 1 hr, after which the animals were returned to the test aquaria. The results are expressed as ml/g dry wt/hr. An analysis of variance is given in Table 1. The seawater used in each experimental chamber was collected for nitrogen analysis. With the completion of the series of experiments the animals were killed, the flesh excised and dried at 100°C to a constant weight. Nitrogen was determined by Kjeldahl digestion followed by colorometric determination as described by Solorzano (1969). The results are expressed as #g N/g dry wt/hr. An analysis of variance is given in Table 2. Byssal formation was observed daily recording the percentage of animals forming byssus (Van Winkle, 1970). Mortality was established when the adductor muscles were no longer functional and the valves remained open.
MATERIALS AND METHODS
RESULTS
Animals selectecl for this study were from a population located at the EI-Kura lagoon 160 km south of Elat (Red
The effects of temperature on oxygen uptake are shown in Fig. 1. Initial increases in oxygen uptake were observed at both 2 7 and 33°C. At 27°C, the increased rate of oxygen uptake persisted for several days longer than at 33°C, where oxygen uptake fell
*Present address: Department of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel. 101
S. STERN AND Y. ACHITUV
102
Table 1. Brachidontes variabilis, analysis of variance for oxygen consumption determinations
Source of variation
Sums of squares 1.55 1.83
Between individuals in: Fig. 1 Fig. 4
df
Mean square
S.D.
Coefficient of variation (%)
6 6
0.26 0.304
0.04798 0.13138
10.240 26.052
Table 2. Brachidontes variabilis, analysis of variance for nitrogen excretion determinations
Source of variation
Sums of squares
Between individuals in: Fig. 2 Fig. 5
21951.10 57058.61
rapidly after the initial increase. A subsequent decrease in oxygen uptake was observed at both temperatures and the rate fell below the acclimatory level (represented as the regression line in Fig. 1), 0.27 ml O2/g dry wt/hr at 27°C and 0.15 ml O2/g dry wt/hr at 33°C. As a result of the high test temperatures, nitrogen excretion increased above the initial level (Fig. 2). The net increase in nitrogen excreted was considerably higher at 33 than at 27°C. All animals introduced to either 27 or 33°C ceased byssal formation for at least the initial 24 hr. At 27°C, byssal formation recovered partially 4 days after the start of the experiment. At a later stage, byssal formation was 65% (Fig, 3). Animals at 33°C did not exhibit any signs of recovery and byssal formation remained zero for the duration of the experiment. At 33°C, the first incidence of mortality was recorded 13 days after the start of the experiment (Table 1), At 27°C, the first mortality was found on the 26th day, and by the 96th day 50% of the animals were dead (Table 1).
df
Mean square
S.D.
Coefficient of variation (%)
3 3
7317.03 19019.54
22.81 17.03
32.360 14.402
The effects of salinity on oxygen uptake are shown in Fig. 1. At 47%o, the rate of oxygen uptake decreased and levelled off at 0.33 ml O2/g dry wt/hr. A decrease in oxygen uptake was also observed at 58%0 where the rate declined to 0.30 ml Oz/g dry wt/hr (Fig. 1). Excretion of nitrogen increased at both salinities (Fig. 2). The net amounts excreted did not differ significantly at 47 and 58%0. Partial recovery of byssa.l formation was observed at 47 and 58%o (Fig. 3). At 4 7 ~ 25% of byssal formation was attained within the initial 24 hr. Several days later the rate increased to 50%. Byssal formation was active at 58%0, where after 5 days 75% formed byssal attachments. For the period of 100 days no mortality was observed at either salinity (Table 1). The combined effects of temperature and salinity on oxygen uptake are shown in Fig. 4. Oxygen uptake of animals transferred to 27°C and 47%0 increased sharply during the initial phases. A few days later, the rate of oxygen uptake declined towards the pretest acclimatory level of 0.47 ml O2/g dry wt/hr, Animals at 27°C and 58%0 initially increased their consumption and at a later stage decreased their rate to 0.47 ml O2/g dry wt/hr. Oxygen uptake at 33°C and 47%o showed initial fluctuations followed by a decline in the rate towards the pretest acclimatory level. At 300
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Temperature and salinity effects on Brachiclontes
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33°C and 58%0, oxygen uptake decreased initially for was observed on the 54th day, with only 50% of the the first few days. The rate established itself at a larger animals dying by the 98th day. At 27°C and 47%0, stage at about 0.40 ml O2/g dry wt/hr. the first mortality was found on the 50th day, when, The effects of combined increases in temperature after the 64th day, 50% of the animals died. Two morand salinity on nitrogen excretion are shown in Fig. talities were observed at 33°C and 58%o, the first 5. Nitrogen excretion at 27°C and 47%0 was in the occurring on the 47th day, with the second following range of 100-150#g N/g dry wt/hr, representing an 8 days later. , overall increase in nitrogen excretion. At 27°C and 58%0, nitrogen excretion initially increased followed DISCUSSION by a decrease to 80 #g N/g dry wt/hr. A sharp decrease in nitrogen excretion was observed at 33°C and In our experiments, the increase in temperature 47%0, where 235 #g N/g dry wt/hr was recorded. produced marked initial increases or overshoots in Nitrogen excretion at 33°C and 58%0 increased to oxygen uptake. Newell & Pye (1971).and Somero & 214/zg N/g dry wt/hr. Hochachka (1971) explain such changes as modificaAt most of the temperature-salinity combinations, tions in enzymatic activity. The activation of certain byssal activity recovered partially (Fig. 6) as com- heat sensitive enzymes or isoenzymes as a result of pared to the acclimation conditions (41%o, 21°C) increasing the temperature probably produces a conwhere byssal formation was 100%. We found that at dition where energy is consumed in order to attain 27°C and 47%o formation reached a maximum of and re-establish a steady state. 62.5% after 12 days. At 27°C and 58%0, byssal formaThe decrease in the rate of oxygen uptake noted tion was 62.5% after 13 days, and at 33°C and 47%o several days later represented initial phases in accliafter 15 days• Byssal formation at 33°C and 58%o in- mation as suggested by Bayne (1975) and other creased to 87.5% after 12 days; however, 2 days later workers. However, the decrease in oxygen uptake it decreased to 62.5%. below the pretest acclimatory level reveals that a conOn the 34th day of the experiment, the first inci- dition of hypercompensation existed as outlined by dence of mortality was observed at 33°C at 47%0. All Precht (1973). the remaining animals in this group died by the 82nd The increase in nitrogen excretion found in these day (Table 1). The first mortality at 27°C and 58%o conditions reflects enhanced protein utilization, as was shown in Mytilus edulis (Bayne & Thompson, 1970). Furthermore, the effect of temperature was greater at 33°C than at 27°C. The continued expenditure of protein produced conditions where the normal activity of the animals was affected, as expressed in the cessation of byssal formation. Byssal threads are o
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,'.~':~.-z as a function of combined increases in temperature and salinity. ,• at pretest conditions 21°C; $ = 42?/o0,cali',, I I I I I i I i I I I I I I t i I 5 IO 15 20 culated regression line y = 0.0189x + 0.461. rq---U] aniDoys mals transferred to 27°C and 47~/~. • . . . . . • transferred to 27°C and 58~/~. A - - . - - A transferred to 33°C and 47%~ Fig• 6. Brachidontes variabilis, changes in byssal formation as a function of combined increases in temperature and • ..... • transferred to 33°C and 58?00. Each point is the mean of three readings of eight animals recorded together. salinity. For explanation of symbols see Fig. 4.
104
S. STERNAND Y. ACHITUV Table 3. Brachidontes variabilis mortality, days required to reach stated percent mortality at given temperature and salinity. Eight animals in each test Conditions Temp. Salinity (°C) (%0) 22 27 33 22 22 27 27 33 33
41 41 41 47 58 47 58 47 58
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known to consist of conchiolin, a molecular complex regime. Comparison of survival for combinations of with a protein component (Brown, 1952). Therefore, 33°C and 41~oo; 33°C and 47%0; and 33°C and 58%0, the continuous energy drain probably limited the clearly reflect the strong beneficial aspect of salinity amount of substrate material required for the byssal in the temperature-salinity combinations (Table 1). Temperature-salinity relationships of a similar secretion. The extent of damage is illustrated by the fact that, at 33°C, all the animals died during the nature are reviewed by Kinne (t964a, b, 1971a, b). For example, Gammarus deubeni is able to tolerate higher experiment, while, at 27°C, only 50% died. A decline in the rate of oxygen uptake as a result temperatures at high salinities. Similarly, McLeese of an increase in salinity is not uncommon in marine (1956) reported that the upper lethal temperature is euryhaline organisms. In experiments on Mytilus lowered by a decrease in salinity in Homarus ameriedulis, for example, a decrease in oxygen uptake was c a n u s . observed after a change in the salinity regime (SchIt is suggested that the pattern of acclimation and lieper, 1955; Potts & Parry, 1963; Beliavev & Tsche- the range of survival is modified by salinity. High gonova, !952, quoted in Staaland, 1972). In this con- temperatures will increase the intensity of salt and text, Mytilus edulis is reported to have an optimal water exchanges beyond the range of active transport, respiratory rate in water of a salinity within the range thereby affecting steady-state exchanges. At higher normally found at their natural habitat (Staaland, salinities, the water content entering the organism is 1972). In our experiments, both-salinity increases lessened, reducing the effects of temperature. On the resulted in a decline in oxygen uptake with an appar- other hand, a lower salinity will cause greater ent stabilization of the lowered metabolic rate. amounts of water to enter, thereby decreasing heat Marine bivalves acting as osmoconformers are in- resistance. capable of anisosmotic regulation (Lange, 1968, 1972). The pattern of metabolic adaptation in BrachiTheir capacity for euryhalinity is believed to be made dontes variabilis is consistent with the demands of the possible in part by volume regulation on an intracel- environment. Water in the lagoons populated by B. lular level (Bayne, 1975). Volume regulation produces variabilis rarely increases in temperature without conchanges in the concentration of intracellular amino comitant increases in salinity. The ability of this acids and other organic molecules. In this respect, species to cross the Suez Canal and enter the Mediterthe increased degradation of amino acids during ranean reflects the extreme versatility of B. variabilis. osmotic adjustments may have led to the increase in Records of the various temperatures and salinities in nitrogen excreted. this area indicate that the environmental barriers A further assessment of the physiological cost of present were not of a magnitude which may have preosmotic stress and adjustment is vividly expressed in vented B. variabilis from entering the Mediterranean the rate of byssal formation and recovery. It was clear Sea (Ashbel, 1950; Por, 1972). In this respect, as in our results that byssal activity was not at a 100% expressed in the laboratory experiments, it seems that level. However, the rate of recovery was compara- B. variabilis is best equipped for bodies of water tively high. The long-range effect did not result in where the salinities are high with varying temperaany mortalities, suggesting that the animals were able tures, rather than high temperatures with low or to adapt to their new salinity regimes. steady salinities. Combinations of temperature and salinity increAcknowled#ements--It is a pleasure to thank Professor ments simultaneously affecting enzymatic activity and F. D. Por and Professor A. Borut for their assistance and inducing intracellular osmotic regulation, may poss- criticism of this paper. ibly modify certain adaptive patterns. The return of oxygen uptake to the acclimation rate at all temperaREFERENCES ture-salinity combinations (Fig. 6), suggests that the ASHBELD. (1950) Bioclimatic Atlas of Israel and the Near animals adapted to their environment, but increases East, Jerusalem. Meteorological Department, Hebrew in nitrogen excreted and incomplete recovery of bysUniversity of Jerusalem. sal formation as well as mortality may suggest incom- B~O~ASHA. & DANIN Z. (1972) The Indo-Pacific species plete adaptation. of Mollusca in the Mediterranean and notes on a A close evaluation of the rate of mortality reveals collection from the Suez Canal. Israel J. Zool. 21, 301-374. that survival was greatly modified by the salinity
Temperature and salinity effects on Brachidontes
105
BAY~ B. L. (1975) Aspects of physiological conditions in LANGE R. (1972) Some recent work on osmotic, ionic and Mytilus edulis L., with special reference to the effects volume regulation in marine animals. Oceanogr. mar. of oxygen tension and salinity. Proc. 9th Europ. mar. Biol. A. Rev. (Edited by BARNESH.), 10, 97-136. biol. Syrup. (Edited by BARNES H.), pp. 213-238. McLEEsE D. W. (1956) Effects of temperature and oxygen Aberdeen University Press, Aberdeen. on the survival of the American lobster. J. Fish. Res. BAY~,r~B. L. & T.OMPSON R. J. (1970) Some physiological Bd Can. 13(2), 227-272. consequences of keeping Mytilus edulis in the laboratory. NEWELL R. C. & P ~ V. I. (1971) The inttuence of thermal Helooliinder wiss. Meeresunters. 20, 526-552. acclimation on the relation between oxygen BROWN C. H. (1952) Some structural proteins of Mytilus consumption and temperature in Littorina littorea (L), edulis. J. miO'osc. Sci. 93, 487-502. and Mytilus edulis (L), Comp. Biochem. Physiol. 34, DAVIESP. (1966) A constant pressure respirometer for use 385-397. with medium sized animals. Oikos 17, 108-112. POR F. D. (1972) Hydrobiological notes on the GAnnOT P. A. & BAYlqE B. L. (1973) Biochemical effects high-salinity waters of the Sinai Peninsula. Mar. Biol. of temperature and nutritive stress on Mytilus edulis L. 14, 111-119. J. mar. biol. Ass. U.K. 53, 269-286. • POTTS W. T. W. & PARRY G. (1963) Osmotic and Ionic KIN~,~ O. (1963) Salinity, osmoregulation and distribution Regulation in Animals. Pergamon Press, Oxford. in macroscopic crustacea. In Marine Distributions P ~ c , T H. (1973) The normal temperature range. In (Edited by DUNnAR M. J.). Ray Soc. Canada Spec. 5, Temperature and Life (Edited by PREC'HT H., CHRISTOPHERSON J., HENSEL H. & LARCHER W.), pp. 30295-105. 353. Springer-Verlag, Berlin. KINNE O. (1964a) Physiologische und Okilogische Aspekte des Lebens in Estuarien. Helgol~nder wiss. Meeresunters. Sere.lEPER C. (1955) Uber die physiologischen Wirkungen 131, 11. des Brackwassers (nach Versuchen an der Miesmuschel KXNNE O. (1964b) The effects of temperature and salinity Mytilus edulis). Kieler Meeresforsch. 11, 23-33. on marine and brackish water animals. Ii. Salinity and SOLORZA~O L. (1969) Determination of ammonia in temperature-salinity combinations. Oceanogr. mar. Biol. natural waters by phenol-hypochlorite method. Limnol. A. Rev. (Edited by BARN~SH.), 2, 281-339. Oceanogr. 14, 799-801. KlN~rr O. (1971a) Temperature: invertebrates. In Marine SO,taRO G. N. & HOCHACHKAD. W. (1971) Biochemical Ecology (Edited by KINN1/ O.), Vol. 1, Part 1, pp. adaptation to the environment. Am. Zool. 11, 157-167. 407-514. Wiley-Interscience, New York. STAALAND H. (1972) Respiratory rate and salinity KINNE O. (1971b) Salinity: invertebrates In Marine preference to the ecology of three marine prosobranchs: Ecology (Edited by KIN~qE O.), Vol. 1, Part 2, pp. Buccinum undatum L., Neptuna antiqua L., and Neptunea 821-996. Wiley-Interscience, New York. despecta L. Norw. J. Zool. 20, 35-50. LANGE R. (1968) The relation between the oxygen VAN WINKLEW. JR (1970) Effect of environmental factors consumption of isolated gill tissue of the common on byssal thread formation. Mar. Biol. 7, 143-148. mussel, Mytilus edulis L. and salinity. J. exp. mar. Biol. VERNSERG W. B. & VERNBERGF. J. (1972) Environmental Ecol. 2, 37-45. Physiology of Marine Animals. Springer Verlag, New York.
EFFECTS OF TEMPERATURE A N D SALINITY ON THE METABOLISM A N D BYSSAL FORMATION OF BRACHIDONTES VARIABILIS KRAUSS (BIVALVIA) S. STERN and Y. ACHXTUV* Department of Zoology, The Hebrew University of Jerusalem, Jerusalem, Israel
(Received 22 March 1977) Al~traet--The effects of temperature and salinity on Brachidontes variabilis were studied. Increase in temperature from 27 to 33°C resulted in a net decrease in oxygen uptake. Salinity increments from 47 to 5 8 ~ resulted in a decrease in oxygen uptake with an apparent stabilization indicating adaptation. Combined increases in temperature and salinity resulted in initial fluctuations in oxygen uptake (either overshoot or undershoot), followed by a return to the pretest rate of oxygen uptake. 2. Nitrogen excretion increased in most of the experiments indicating enhanced utilization of proteins. Correlation was found between byssal formation (percentage of animals forming byssus) and the degree of stress imposed on the animals. 3. Mortality and survival were modified by the salinity regime imposed. Thermal tolerance significantly increased in high salinities. It is suggested that the osmoconforming ability of B. variabilis is responsible for such a relationship. 4. The metabolic plasticity of B. variabilis as expressed in this study is believed to have played a major role in its ability to migrate into the Mediterranean Sea.
INTRODUCTION Temperature and salinity are important environmental factors affecting the distribution of a wide range of marine organisms. The intertidal zone in particular is subjected to wide temperature and salinity fluctuations. The effects of temperature and salinity on intertidal organisms are reviewed by Kinne (1963, 1964a, b, 1971a, b). The mechanisms essential for life in the intertidal zone are summed up by Vernberg & Vernberg (1972~ Along the Sinai Peninsula there are a number of lagoons and other water bodies where temperature and salinity fluctuations are outstanding (Por, 1972). One of the most common animals there, the bivalve mollusc Brachidontes variabilis Krauss, is categorized as belonging to a marine assemblage of hyperhaline organisms (Por, 1972). With the opening of the Suez Canal, the Mediterranean and Red Sea came into direct c o n t a c t and this gave rise to faunal migrations. Brachidontes variabilis, a Red Sea species, has now reached the eastern Mediterranean (Barash & Danin, 1972). By evaluating some of the ecophysiological characteristics of Brachidontes variabilis, some insight may be gained as to the nature by which B. variabilis was successful in migrating into the Mediterranean Sea. The laboratory experiments involved studies on oxygen uptake, nitrogen excretion and byssal formation, with the view of determining the role of temperature and salinity in the ecology of Brachidontes variabilis.
Sea). All specimens selected were of size 23-26 mm. (maximum length of the shell)~ Experiments were carried out in Jerusalem in aquaria of 501. capacity with re-circulating seawater. Animals were not fed artificially, nor was the water in each aquarium passed through a selective filter. Prior to each experiment, all animals were acclimated to 21°C and 42%o for at least 2 weeks. Salinities were monitored by a Beckman Salinometer model RS-7B. Temperatures in the aquaria were maintained by an immersed heating element to a precision of +I°C. Eight experimental regimes were tested with eight animals in each experiment. Eight additional animals were transferred to each aquarium for reserve purposes. Oxygen uptake was determined by a Davies constant pressure respirometer (Davies, 1966). Animals were equilibrated for 1 hr prior to each reading of oxygen uptake. With the completion of the equilibration period, oxygen uptake was recorded in 15 rain intervals over 1 hr, after which the animals were returned to the test aquaria. The results are expressed as ml/g dry wt/hr. An analysis of variance is given in Table 1. The seawater used in each experimental chamber was collected for nitrogen analysis. With the completion of the series of experiments the animals were killed, the flesh excised and dried at 100°C to a constant weight. Nitrogen was determined by Kjeldahl digestion followed by colorometric determination as described by Solorzano (1969). The results are expressed as #g N/g dry wt/hr. An analysis of variance is given in Table 2. Byssal formation was observed daily recording the percentage of animals forming byssus (Van Winkle, 1970). Mortality was established when the adductor muscles were no longer functional and the valves remained open.
MATERIALS AND METHODS
RESULTS
Animals selectecl for this study were from a population located at the EI-Kura lagoon 160 km south of Elat (Red
The effects of temperature on oxygen uptake are shown in Fig. 1. Initial increases in oxygen uptake were observed at both 2 7 and 33°C. At 27°C, the increased rate of oxygen uptake persisted for several days longer than at 33°C, where oxygen uptake fell
*Present address: Department of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel. 101
S. STERN AND Y. ACHITUV
102
Table 1. Brachidontes variabilis, analysis of variance for oxygen consumption determinations
Source of variation
Sums of squares 1.55 1.83
Between individuals in: Fig. 1 Fig. 4
df
Mean square
S.D.
Coefficient of variation (%)
6 6
0.26 0.304
0.04798 0.13138
10.240 26.052
Table 2. Brachidontes variabilis, analysis of variance for nitrogen excretion determinations
Source of variation
Sums of squares
Between individuals in: Fig. 2 Fig. 5
21951.10 57058.61
rapidly after the initial increase. A subsequent decrease in oxygen uptake was observed at both temperatures and the rate fell below the acclimatory level (represented as the regression line in Fig. 1), 0.27 ml O2/g dry wt/hr at 27°C and 0.15 ml O2/g dry wt/hr at 33°C. As a result of the high test temperatures, nitrogen excretion increased above the initial level (Fig. 2). The net increase in nitrogen excreted was considerably higher at 33 than at 27°C. All animals introduced to either 27 or 33°C ceased byssal formation for at least the initial 24 hr. At 27°C, byssal formation recovered partially 4 days after the start of the experiment. At a later stage, byssal formation was 65% (Fig, 3). Animals at 33°C did not exhibit any signs of recovery and byssal formation remained zero for the duration of the experiment. At 33°C, the first incidence of mortality was recorded 13 days after the start of the experiment (Table 1), At 27°C, the first mortality was found on the 26th day, and by the 96th day 50% of the animals were dead (Table 1).
df
Mean square
S.D.
Coefficient of variation (%)
3 3
7317.03 19019.54
22.81 17.03
32.360 14.402
The effects of salinity on oxygen uptake are shown in Fig. 1. At 47%o, the rate of oxygen uptake decreased and levelled off at 0.33 ml O2/g dry wt/hr. A decrease in oxygen uptake was also observed at 58%0 where the rate declined to 0.30 ml Oz/g dry wt/hr (Fig. 1). Excretion of nitrogen increased at both salinities (Fig. 2). The net amounts excreted did not differ significantly at 47 and 58%0. Partial recovery of byssa.l formation was observed at 47 and 58%o (Fig. 3). At 4 7 ~ 25% of byssal formation was attained within the initial 24 hr. Several days later the rate increased to 50%. Byssal formation was active at 58%0, where after 5 days 75% formed byssal attachments. For the period of 100 days no mortality was observed at either salinity (Table 1). The combined effects of temperature and salinity on oxygen uptake are shown in Fig. 4. Oxygen uptake of animals transferred to 27°C and 47%0 increased sharply during the initial phases. A few days later, the rate of oxygen uptake declined towards the pretest acclimatory level of 0.47 ml O2/g dry wt/hr, Animals at 27°C and 58%0 initially increased their consumption and at a later stage decreased their rate to 0.47 ml O2/g dry wt/hr. Oxygen uptake at 33°C and 47%o showed initial fluctuations followed by a decline in the rate towards the pretest acclimatory level. At 300
05
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Fig. 2. Brachidontes variabilis, changes in nitrogen e x c r e t i o n a s a f u n c t i o n o f increases in temperature and salinity; for explanation of symbols see Fig. 1.
Temperature and salinity effects on Brachiclontes
103
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Fig. 5. Brachidontes variabilis, changes in nitrogen excretion as a function of combined increases in temperature and salinity. For explanation of symbols see Fig. 4.
33°C and 58%0, oxygen uptake decreased initially for was observed on the 54th day, with only 50% of the the first few days. The rate established itself at a larger animals dying by the 98th day. At 27°C and 47%0, stage at about 0.40 ml O2/g dry wt/hr. the first mortality was found on the 50th day, when, The effects of combined increases in temperature after the 64th day, 50% of the animals died. Two morand salinity on nitrogen excretion are shown in Fig. talities were observed at 33°C and 58%o, the first 5. Nitrogen excretion at 27°C and 47%0 was in the occurring on the 47th day, with the second following range of 100-150#g N/g dry wt/hr, representing an 8 days later. , overall increase in nitrogen excretion. At 27°C and 58%0, nitrogen excretion initially increased followed DISCUSSION by a decrease to 80 #g N/g dry wt/hr. A sharp decrease in nitrogen excretion was observed at 33°C and In our experiments, the increase in temperature 47%0, where 235 #g N/g dry wt/hr was recorded. produced marked initial increases or overshoots in Nitrogen excretion at 33°C and 58%0 increased to oxygen uptake. Newell & Pye (1971).and Somero & 214/zg N/g dry wt/hr. Hochachka (1971) explain such changes as modificaAt most of the temperature-salinity combinations, tions in enzymatic activity. The activation of certain byssal activity recovered partially (Fig. 6) as com- heat sensitive enzymes or isoenzymes as a result of pared to the acclimation conditions (41%o, 21°C) increasing the temperature probably produces a conwhere byssal formation was 100%. We found that at dition where energy is consumed in order to attain 27°C and 47%o formation reached a maximum of and re-establish a steady state. 62.5% after 12 days. At 27°C and 58%0, byssal formaThe decrease in the rate of oxygen uptake noted tion was 62.5% after 13 days, and at 33°C and 47%o several days later represented initial phases in accliafter 15 days• Byssal formation at 33°C and 58%o in- mation as suggested by Bayne (1975) and other creased to 87.5% after 12 days; however, 2 days later workers. However, the decrease in oxygen uptake it decreased to 62.5%. below the pretest acclimatory level reveals that a conOn the 34th day of the experiment, the first inci- dition of hypercompensation existed as outlined by dence of mortality was observed at 33°C at 47%0. All Precht (1973). the remaining animals in this group died by the 82nd The increase in nitrogen excretion found in these day (Table 1). The first mortality at 27°C and 58%o conditions reflects enhanced protein utilization, as was shown in Mytilus edulis (Bayne & Thompson, 1970). Furthermore, the effect of temperature was greater at 33°C than at 27°C. The continued expenditure of protein produced conditions where the normal activity of the animals was affected, as expressed in the cessation of byssal formation. Byssal threads are o
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,'.~':~.-z as a function of combined increases in temperature and salinity. ,• at pretest conditions 21°C; $ = 42?/o0,cali',, I I I I I i I i I I I I I I t i I 5 IO 15 20 culated regression line y = 0.0189x + 0.461. rq---U] aniDoys mals transferred to 27°C and 47~/~. • . . . . . • transferred to 27°C and 58~/~. A - - . - - A transferred to 33°C and 47%~ Fig• 6. Brachidontes variabilis, changes in byssal formation as a function of combined increases in temperature and • ..... • transferred to 33°C and 58?00. Each point is the mean of three readings of eight animals recorded together. salinity. For explanation of symbols see Fig. 4.
104
S. STERNAND Y. ACHITUV Table 3. Brachidontes variabilis mortality, days required to reach stated percent mortality at given temperature and salinity. Eight animals in each test Conditions Temp. Salinity (°C) (%0) 22 27 33 22 22 27 27 33 33
41 41 41 47 58 47 58 47 58
12.5 . 26 14 . . 50 55 34 47
25 .
Mortality 50 62.5
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. 22 20 .
. . 64 98 52 .
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. 96
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.
known to consist of conchiolin, a molecular complex regime. Comparison of survival for combinations of with a protein component (Brown, 1952). Therefore, 33°C and 41~oo; 33°C and 47%0; and 33°C and 58%0, the continuous energy drain probably limited the clearly reflect the strong beneficial aspect of salinity amount of substrate material required for the byssal in the temperature-salinity combinations (Table 1). Temperature-salinity relationships of a similar secretion. The extent of damage is illustrated by the fact that, at 33°C, all the animals died during the nature are reviewed by Kinne (t964a, b, 1971a, b). For example, Gammarus deubeni is able to tolerate higher experiment, while, at 27°C, only 50% died. A decline in the rate of oxygen uptake as a result temperatures at high salinities. Similarly, McLeese of an increase in salinity is not uncommon in marine (1956) reported that the upper lethal temperature is euryhaline organisms. In experiments on Mytilus lowered by a decrease in salinity in Homarus ameriedulis, for example, a decrease in oxygen uptake was c a n u s . observed after a change in the salinity regime (SchIt is suggested that the pattern of acclimation and lieper, 1955; Potts & Parry, 1963; Beliavev & Tsche- the range of survival is modified by salinity. High gonova, !952, quoted in Staaland, 1972). In this con- temperatures will increase the intensity of salt and text, Mytilus edulis is reported to have an optimal water exchanges beyond the range of active transport, respiratory rate in water of a salinity within the range thereby affecting steady-state exchanges. At higher normally found at their natural habitat (Staaland, salinities, the water content entering the organism is 1972). In our experiments, both-salinity increases lessened, reducing the effects of temperature. On the resulted in a decline in oxygen uptake with an appar- other hand, a lower salinity will cause greater ent stabilization of the lowered metabolic rate. amounts of water to enter, thereby decreasing heat Marine bivalves acting as osmoconformers are in- resistance. capable of anisosmotic regulation (Lange, 1968, 1972). The pattern of metabolic adaptation in BrachiTheir capacity for euryhalinity is believed to be made dontes variabilis is consistent with the demands of the possible in part by volume regulation on an intracel- environment. Water in the lagoons populated by B. lular level (Bayne, 1975). Volume regulation produces variabilis rarely increases in temperature without conchanges in the concentration of intracellular amino comitant increases in salinity. The ability of this acids and other organic molecules. In this respect, species to cross the Suez Canal and enter the Mediterthe increased degradation of amino acids during ranean reflects the extreme versatility of B. variabilis. osmotic adjustments may have led to the increase in Records of the various temperatures and salinities in nitrogen excreted. this area indicate that the environmental barriers A further assessment of the physiological cost of present were not of a magnitude which may have preosmotic stress and adjustment is vividly expressed in vented B. variabilis from entering the Mediterranean the rate of byssal formation and recovery. It was clear Sea (Ashbel, 1950; Por, 1972). In this respect, as in our results that byssal activity was not at a 100% expressed in the laboratory experiments, it seems that level. However, the rate of recovery was compara- B. variabilis is best equipped for bodies of water tively high. The long-range effect did not result in where the salinities are high with varying temperaany mortalities, suggesting that the animals were able tures, rather than high temperatures with low or to adapt to their new salinity regimes. steady salinities. Combinations of temperature and salinity increAcknowled#ements--It is a pleasure to thank Professor ments simultaneously affecting enzymatic activity and F. D. Por and Professor A. Borut for their assistance and inducing intracellular osmotic regulation, may poss- criticism of this paper. ibly modify certain adaptive patterns. The return of oxygen uptake to the acclimation rate at all temperaREFERENCES ture-salinity combinations (Fig. 6), suggests that the ASHBELD. (1950) Bioclimatic Atlas of Israel and the Near animals adapted to their environment, but increases East, Jerusalem. Meteorological Department, Hebrew in nitrogen excreted and incomplete recovery of bysUniversity of Jerusalem. sal formation as well as mortality may suggest incom- B~O~ASHA. & DANIN Z. (1972) The Indo-Pacific species plete adaptation. of Mollusca in the Mediterranean and notes on a A close evaluation of the rate of mortality reveals collection from the Suez Canal. Israel J. Zool. 21, 301-374. that survival was greatly modified by the salinity
Temperature and salinity effects on Brachidontes
105
BAY~ B. L. (1975) Aspects of physiological conditions in LANGE R. (1972) Some recent work on osmotic, ionic and Mytilus edulis L., with special reference to the effects volume regulation in marine animals. Oceanogr. mar. of oxygen tension and salinity. Proc. 9th Europ. mar. Biol. A. Rev. (Edited by BARNESH.), 10, 97-136. biol. Syrup. (Edited by BARNES H.), pp. 213-238. McLEEsE D. W. (1956) Effects of temperature and oxygen Aberdeen University Press, Aberdeen. on the survival of the American lobster. J. Fish. Res. BAY~,r~B. L. & T.OMPSON R. J. (1970) Some physiological Bd Can. 13(2), 227-272. consequences of keeping Mytilus edulis in the laboratory. NEWELL R. C. & P ~ V. I. (1971) The inttuence of thermal Helooliinder wiss. Meeresunters. 20, 526-552. acclimation on the relation between oxygen BROWN C. H. (1952) Some structural proteins of Mytilus consumption and temperature in Littorina littorea (L), edulis. J. miO'osc. Sci. 93, 487-502. and Mytilus edulis (L), Comp. Biochem. Physiol. 34, DAVIESP. (1966) A constant pressure respirometer for use 385-397. with medium sized animals. Oikos 17, 108-112. POR F. D. (1972) Hydrobiological notes on the GAnnOT P. A. & BAYlqE B. L. (1973) Biochemical effects high-salinity waters of the Sinai Peninsula. Mar. Biol. of temperature and nutritive stress on Mytilus edulis L. 14, 111-119. J. mar. biol. Ass. U.K. 53, 269-286. • POTTS W. T. W. & PARRY G. (1963) Osmotic and Ionic KIN~,~ O. (1963) Salinity, osmoregulation and distribution Regulation in Animals. Pergamon Press, Oxford. in macroscopic crustacea. In Marine Distributions P ~ c , T H. (1973) The normal temperature range. In (Edited by DUNnAR M. J.). Ray Soc. Canada Spec. 5, Temperature and Life (Edited by PREC'HT H., CHRISTOPHERSON J., HENSEL H. & LARCHER W.), pp. 30295-105. 353. Springer-Verlag, Berlin. KINNE O. (1964a) Physiologische und Okilogische Aspekte des Lebens in Estuarien. Helgol~nder wiss. Meeresunters. Sere.lEPER C. (1955) Uber die physiologischen Wirkungen 131, 11. des Brackwassers (nach Versuchen an der Miesmuschel KXNNE O. (1964b) The effects of temperature and salinity Mytilus edulis). Kieler Meeresforsch. 11, 23-33. on marine and brackish water animals. Ii. Salinity and SOLORZA~O L. (1969) Determination of ammonia in temperature-salinity combinations. Oceanogr. mar. Biol. natural waters by phenol-hypochlorite method. Limnol. A. Rev. (Edited by BARN~SH.), 2, 281-339. Oceanogr. 14, 799-801. KlN~rr O. (1971a) Temperature: invertebrates. In Marine SO,taRO G. N. & HOCHACHKAD. W. (1971) Biochemical Ecology (Edited by KINN1/ O.), Vol. 1, Part 1, pp. adaptation to the environment. Am. Zool. 11, 157-167. 407-514. Wiley-Interscience, New York. STAALAND H. (1972) Respiratory rate and salinity KINNE O. (1971b) Salinity: invertebrates In Marine preference to the ecology of three marine prosobranchs: Ecology (Edited by KIN~qE O.), Vol. 1, Part 2, pp. Buccinum undatum L., Neptuna antiqua L., and Neptunea 821-996. Wiley-Interscience, New York. despecta L. Norw. J. Zool. 20, 35-50. LANGE R. (1968) The relation between the oxygen VAN WINKLEW. JR (1970) Effect of environmental factors consumption of isolated gill tissue of the common on byssal thread formation. Mar. Biol. 7, 143-148. mussel, Mytilus edulis L. and salinity. J. exp. mar. Biol. VERNSERG W. B. & VERNBERGF. J. (1972) Environmental Ecol. 2, 37-45. Physiology of Marine Animals. Springer Verlag, New York.