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Salinity tolerance or marine organisms deduced from Red Sea Quaternary record
Marine Geology, 53 (1983) M17--M22
M17
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands L e t t e r Section S ALI NI TY T O L E R A N C E O R MARINE ORGANISMS DEDUCED FROM RED SEA Q U A T E R N A R Y R E C O R D
AMOS WINTERt *, AHUVA ALMOGI-LABIN1 , YONATHAN EREZ2 , ELVIRA HALICZ 1, BOAZ LUZ 1 and ZEEV REISS 1 1Department of Geology, Institute of Earth Sciences, The Hebrew University of Jerusalem (Israel) 2H. Steinitz Marine Biological Laboratory, The Hebrew University, Elat (Israel)
(Received March 15, 1983; revised and accepted June 13, 1983)
ABSTRACT
Winter, A., Almogi-Labin, A., Eraz, Y., Halicz, E., Luz, B. and Rei~, Z., 1983. Salinity tolerance of marine organisms deduced from Red Sea Quaternary record. Mar. Geol., 53: M17--M22. The oxygen-kotopic record and microfoMils from deep4ea cores raised in the hypersaline (41°/00 salinity) Gulf of Aqaba indicate that during Late Quaternary glacial time salinity rose considerably due to ~a-level fall and strait-dynamics, reaching values of more than 50%o during the last Glacial maximum about 18 Ka B.P. The salinity-dependent sequence of disappearance of various species of foraminifera, pteropods and coccolithophorids can be used to determine upper salinity tolerance limits of different taxa. Only the pteropod Creseb acicu~ and various benthonic foraminifera are able to withstand high ~linities like those during the last glacial maximum.
INTRODUCTION Knowledge o f ecological tolerances, like t e m p e r a t u r e or salinity, o f marine organisms is of i m por t ance t o paleoenvironmental interpretation, using the present as a key t o the past. Experimental data are rather meagre, and m a x i m u m salinity tolerance values k n o w n so far are m ost l y those in which a particular organism has been f o und in present-day seas. T he actual u p p er salinity limit o f an organism may, however, be deduced from its fossil record in ancient sediments deposited in a highly saline marine e n v i r o n m e n t for which n o m o d e m analogue exists, thus using t he past as a key t o t he present. The Gulf o f Aqaba (or Elat), Red Sea, is at present hypersaline ( a b o u t 41.0°/00 salinity; Klinker et al., 1976). Under such conditions m a n y orga*Present addreu: Dept. of Geology (Marine Geoacience), University of Cape Town, Rondebosch 7700, South Africa.
0025-3227/83/$03.00
© Elsevier Science Publishers B.V.
M18 nisms live at the edge of their ecological tolerance (Halicz and Reiss, 1981). Their upper salinity limit has recently been clarified from a study of fossil assemblages in four deep-sea cores raised in the Gulf (Halicz and Reiss, 1981; Almogi-Labin, 1982; Winter, 1983). We have been able to reconstruct the paleoceanographic setting of the Gulf during the last 150,000 years using distribution patterns of pteropods, planktonic and benthonic foraminifera, coccolithophorids and stable oxygen isotopes in the cores (Reiss et al., 1980). Deuser's (1976) method of comparing the 5180 range in planktonic foraminifera between the Gulf of Aden and the Red Sea has been used to infer the paleoceanography of the Gulf during the last glacial maximum (LGM). METHODS AND MATERIALS Core 74 used in this study was taken by the WHOI research vessel "Atlantic II" in 1977 from the relatively flat sea bottom of the southern part of the Gulf of Aqaba. This core is complete over the last glacial--post-glacial cycle and penetrated mostly grey-green, partly silty lutites. It is richly fossiliferous, consisting mostly of coccoliths, foraminifera and pteropods. Recovery of core 74 was satisfactory, except for the piston coretop which was lost. For this reason the records of the trigger-weight cores were combined with those of the piston cores. Considering the high rates of sedimentation recorded from the Red Sea (Ku et al., 1969) the cores were sampled at 10--20 cm intervals by extracting 10 cm s plugs. Samples were washed with water over standard sieves to obtain fractions <63, 63--149, and >149/~m, and oven-dried at 50°C. For coccolith studies the <63-pro fraction was centrifuged with water at 2500 rpm for 45 s. A portion of the deposit was agitated with water and allowed to settle for 5 minutes. A few drops were then placed on an SEM stub and dried before viewing. At least 300 specimens per sample were counted and studied for species identification and morphological observation. The > 149-pm fraction was randomly split and between 200 and 500 specimens of foraminifera and pteropods each were identified and counted. DISCUSSION The 61sO curves in the open ocean in the Gulf of Aden and the Red Sea are very similar, suggesting the isotopic composition of sea water as the major factor determining them. However, the global signal is amplified in the Red Sea because of strait dynamics at lowered sea level (Klinker et al., 1976; Reiss et al., 1980). The difference in ~110 in planktonic foraminifera and pteropod shells between the LGM and the present is about 1.5°/0o in the open ocean (Sarin and Hsueh-Wen, 1981), 20/00 in the Gulf of Aden (Deuser et al., 1976), and in excess of 5%0 in the Red Sea and the Gulf of Aqaba (Deuser et al., 1976; Reiss et al., 1980). It is unlikely that this latter great
M19
difference can be attributed to significant temperature changes, considering the low-latitude position of the Red Sea (CLIMAP Project Members, 1976). In addition, throughout the core sequences studied from the Gulf of Aqaba, evidence suggests that the minimum temperatures of all the fauna and flora present, especially the known winter isotherms of displaced shallow water, symbiont-bearing benthic foraminifera, did not drop below 17°C. Taking into account that the Gulf of Aqaba is well mixed throughout the year (no thermocline is present except for a short period of slight stratification) and that minimum Gulf temperature is 21°C, the greatest temperature difference between glacials and interglacials in the upper waters most likely did not exceed 4°C. Thus, of the 50/00 81sO glacial--interglacial difference, 1.5°/00 can be explained by global ice volume (Shackleton, 1977) and 1.0°/00 by the 4°C change in temperature (Dansgaard, 1964). This leaves 2.50/00 ~ 180 which is correlatable with an increase of about 10%0 salinity (Craig, 1966). Thus, the salinity of the Gulf probably rose to more than 500/00 during the LGM (Reiss et al., 1980). This extremely high salinity appears to be the cause for the total absence of planktonic foraminifera and coccolithophorids in strata corresponding to the LGM. Considering the abundance of aragonitic pteropods in the same strata, preservation cannot be invoked to explain the absence of low-Mg calcite shells. The large AS laO difference in the benthonic to planktonic foraminiferal ratio has been interpreted to represent increased stratification prior to the LGM (Winter, 1983). Nevertheless, the influence of stratification on the planktonic assemblages present should have been minimal as all planktonic species in the Gulf are epi- and shallow mesopelagic species (Reiss et al., 1980). Temperature seems also not to have been a critical factor since the temperature ranges of the species studies in the Gulf are wide, lying between 14 ° and 30°C (Halicz and Reiss, 1981; Almogi-Labin, 1982; Winter, 1983). Other factors such as food supply have been shown to influence the a~semblage composition of the groups mentioned here throughout the late Quaternary. However, there is no evidence that nutrients diminished to such an extent as to cause total disappearance of the planktonic groups studied. On the contrary, productivity seems to have increased during glacials (see the next section). The extremely rapid change in salinity prior to the LGM leads to the conclusion that salinity was the deciding factor dictating the extinction sequence of the various taxa shown in Fig. 1 and outlined below. Pteropods
Among the calcareous plankton this seems to be the most salinity tolerant group, the genus Creseis being particularly well adapted to high saiinities. C. acicula is the only species studied apparently able to withstand salinities of more than 500/00 (Almogi-Labin, 1982). This species lives today in hyper-saline lagoons with salinities above 450/00 (B~ and Gflmer, 1977). The number of specimens of C. acicula in sediments deposited during the LGM
M20
a~
.
.
~
,,,~,
=,,, .
uf'alxnqD / u p q / ~ •
..-~ o~
-r~
z~q/uoeoop¢doooHqd~cj
~e J~]/]nOOOS S~p OUl2c3~'~/O/~
~..
2~
0
0
~.£
k ~eqn~ sep/ou/~aZ~/qo/~
g,,
~e z~
~ ~,' ~.~.~ ~
Oln~.//~' ~'/~a.~0 • --
k
ao ~=r
0
.0
~
'-',
~.£
~g
o
~N
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.= "IV13V-19 - J.SOd
~ • ~_
4.a
~
~.~_
~ ~ 0
._
O~ ~ C ~ •
4.~
m ~ ~.~ ~ •
M21
in the Aqaba cores is extremely low, indicating that 50o/o0 salinityis approximately the upper tolerance limit for this species. L o w counts of C. acicula cannot be explained by increased terrigenous input or decreased productivity: in fact,relativelylower sedimentation rates during glacialswere determined in the Aqaba cores, while considerations of fossilassemblages (including large diatom floras in the northern Red Sea) indicate heightened productivity of the upper water (Reiss et al.,1980; Halicz and Reiss, 1981; AlmogiLabin, 1982). Creseis virgula and Limacina trochiformis are apparently unable to survive the extreme salinitiesof the L G M , but were abundant during the higher than present glacialsalinities,prior to the L G M . However, L. trochiformis disappears before C. virgula and thus has an apparently lower salinitythreshold. These lattertwo species have been interpreted earlier from Red Sea cores as reflectingtransitionalconditions between normal and highly saline waters (Almogi-Labin, 1982).
Foraminifera No planktonic foraminifera have been found in the Aqaba sediments of the LGM, although benthonic species, especially Miliolidae, are abundant. This latter group, although widely distributed, is known to be c o m m o n in high-salinity environments (such as Persian Gulf lagoons) and in hypersaline mangroves and sebkhas of the Gulf of Aqaba (HaUcz and Reiss, 1981). Among the groups studied, planktonic foraminifera seem to be the least tolerant of high salinities. Only one species, Globigerinoides ruber, is present during the high-salinity conditions prior to the LGM, but it disappears rather early, and immediately after G. saccultfer, with rising salinity. Laboratory experiments carried out on living Globigerinoides saccuUfer from the Gulf of Aqaba, point to an upper tolerance limit of less than 500/00 for this species (Erez, in prep.). This may be, in fact, the upper salinity limit for all planktonic foraminifera.
Coccolithophorids The coccolithophorids living at present in the Gulf of Aqaba and occurring in the cores seem to be well adapted to high salinities. However, no species is able to survive the extreme salinities of the LGM. EmiUania huxleyi was considered up to now to be the most euryhaline species. However, it disappears before Gephyrocapsa oceanica which appears to be more tolerant of high salinities than E. huxleyi. It is noteworthy that in laboratory cultures E. huxleyi was unable to grow in salinities above 450/00 (Mjaaland, 1956). The upper salinity limit of E. huxleyi may be assumed to lie between 41 and 45%0, while that of G. oceanica should lie between 45 and 50o/00. CONCLUSION
This report demonstrates h o w biogenic constituents of marine sediments from ancient highly saline environments, for which no modern analogue
M22 exists, can be used t o deduce uppe r salinity tolerance limits of three different biological groups. Amo n g the coccolithophorids, Gephyrocapsa oceanica seems t o be the only species able t o live in salinities o f a b o u t 50°/00, planktonic foraminifera are apparently unable t o survive salinities o f m ore than a b o u t 48%0, while benthonic foraminifera, especially Mfliolidae, are able t o withstand salinities o f m or e than 50°/oo. Creseis acicula is the only p t e r o p o d (and calcareous planktonic species) surviving salinities of m ore than 50O/oo. ACKNOWLEDGEMENTS S u p p o r ted in part by U.S.A./Israel BSF Grant No. 1 7 6 2 / 7 8 to Z. Reiss, by NSF Gr an t OCE 7 6 8 1 4 8 8 t o Woods Hole Oceanographic Institution, Grant 0 1 5 . 7 1 3 8 (to Z. Reiss) o f the Israel Ministry o f Energy and Intrastructure and by a L ady Davis Fellowship t o A. Winter.
REFERENCES
Almogi-Labin, A., 1982. Stra~ffaph/c and p ~ p h i c si~ficance of Late Quaterrmry pteropods from ~ eor~ in the Gulf of Aqsba (Elat)and northernme6t Red Sea. Mar. Micropsieontol., 7: 53--72. B~, A.W.H. and Gilmer, R.W., 1977. A ~ a p h i e and taxonomic review of euthecosomatous ptaropmis. In: A.T.S. Ramsay (ldRor), Ocean Mkn~pal~ntology. Academic Press, London, Vol. 1, pp. 733--808. Broeckar, W.S. and Van Donk, J., 1970. Insolation c ~ , ice volumm, and the 1'O record in dcep~Na corm. Rev. (;k~hys. 8pace Phys., 8: 169-198. CLIMAP Project Members, 1976. The surface of the ice age Earth. Science, 191 : 1131--1144. Craig, H., 1966. I4otopic composition and origin of the Red Sea and Saiton Sea Goa. Geothermal brinm. Science, 154: 1544--1548. Dansgaard, W., 1964. Stablm kotop~ in precipitation. Tellus, 16: 436--468. Halicz, E. and ReiM, Z., 1981. Paieoecological relations of foraminifera in a desertenclosed sea -- the Gulf of Aqalm (Flat), Red Sea. Mar. Ecol., 2: 15--35. Klinker, J., Rei~, Z., Kropach, C., Levanon, I., Harpaz, H., Halicz, E. and Ammf, G., 1976. Obxrvatim~ on the cireuietion pattern in the Gulf of Aqaba (Elat), Red Sea. I~rael J. Earth-sci., 25: 85--103. Mjaaland, G., 1956. Some laboratory experiments on the coccolithophorid Corcolithus huxleyi. Oikos, 7(2): 251--255. Rei~, Z., Luz, B., Almo~Labin, A., Halicz, E., Winter, A., Wolf, M. and Rom, D.A., 1980. Late Qttatammry paieoceanography of the Gulf of Aqaba (Elat), Red Sea. Quat. R~., 14: 294--308. Sbeeldeton, N.J., 1977. ~he oxylgen kotope stratigraphic record of the Late Pleistocene. Philos. Trine. R. Soc. London, ~mr. B, $[80: 169--182. Sheckloton, N.J. and + ~ e , N.D., 1973. ~ motope and p ~ i c stratigraphy of Kluatorial ~ ~ V28-~ ;oz~ kotolm tmmperatttre and ice volum~ on a 10 s and 10+ year acale. Quat. R~., 3(1): 39--55. Winter, A., 1968. Paieoenvironmmatsl Intmrp~tation of Quaterma7 Coccolith Am~nbiegm from the Gulf of Aqaba (Elat), Red Sea. Rev. Fsp. Micropal., 14: 291--314.
M17
Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands L e t t e r Section S ALI NI TY T O L E R A N C E O R MARINE ORGANISMS DEDUCED FROM RED SEA Q U A T E R N A R Y R E C O R D
AMOS WINTERt *, AHUVA ALMOGI-LABIN1 , YONATHAN EREZ2 , ELVIRA HALICZ 1, BOAZ LUZ 1 and ZEEV REISS 1 1Department of Geology, Institute of Earth Sciences, The Hebrew University of Jerusalem (Israel) 2H. Steinitz Marine Biological Laboratory, The Hebrew University, Elat (Israel)
(Received March 15, 1983; revised and accepted June 13, 1983)
ABSTRACT
Winter, A., Almogi-Labin, A., Eraz, Y., Halicz, E., Luz, B. and Rei~, Z., 1983. Salinity tolerance of marine organisms deduced from Red Sea Quaternary record. Mar. Geol., 53: M17--M22. The oxygen-kotopic record and microfoMils from deep4ea cores raised in the hypersaline (41°/00 salinity) Gulf of Aqaba indicate that during Late Quaternary glacial time salinity rose considerably due to ~a-level fall and strait-dynamics, reaching values of more than 50%o during the last Glacial maximum about 18 Ka B.P. The salinity-dependent sequence of disappearance of various species of foraminifera, pteropods and coccolithophorids can be used to determine upper salinity tolerance limits of different taxa. Only the pteropod Creseb acicu~ and various benthonic foraminifera are able to withstand high ~linities like those during the last glacial maximum.
INTRODUCTION Knowledge o f ecological tolerances, like t e m p e r a t u r e or salinity, o f marine organisms is of i m por t ance t o paleoenvironmental interpretation, using the present as a key t o the past. Experimental data are rather meagre, and m a x i m u m salinity tolerance values k n o w n so far are m ost l y those in which a particular organism has been f o und in present-day seas. T he actual u p p er salinity limit o f an organism may, however, be deduced from its fossil record in ancient sediments deposited in a highly saline marine e n v i r o n m e n t for which n o m o d e m analogue exists, thus using t he past as a key t o t he present. The Gulf o f Aqaba (or Elat), Red Sea, is at present hypersaline ( a b o u t 41.0°/00 salinity; Klinker et al., 1976). Under such conditions m a n y orga*Present addreu: Dept. of Geology (Marine Geoacience), University of Cape Town, Rondebosch 7700, South Africa.
0025-3227/83/$03.00
© Elsevier Science Publishers B.V.
M18 nisms live at the edge of their ecological tolerance (Halicz and Reiss, 1981). Their upper salinity limit has recently been clarified from a study of fossil assemblages in four deep-sea cores raised in the Gulf (Halicz and Reiss, 1981; Almogi-Labin, 1982; Winter, 1983). We have been able to reconstruct the paleoceanographic setting of the Gulf during the last 150,000 years using distribution patterns of pteropods, planktonic and benthonic foraminifera, coccolithophorids and stable oxygen isotopes in the cores (Reiss et al., 1980). Deuser's (1976) method of comparing the 5180 range in planktonic foraminifera between the Gulf of Aden and the Red Sea has been used to infer the paleoceanography of the Gulf during the last glacial maximum (LGM). METHODS AND MATERIALS Core 74 used in this study was taken by the WHOI research vessel "Atlantic II" in 1977 from the relatively flat sea bottom of the southern part of the Gulf of Aqaba. This core is complete over the last glacial--post-glacial cycle and penetrated mostly grey-green, partly silty lutites. It is richly fossiliferous, consisting mostly of coccoliths, foraminifera and pteropods. Recovery of core 74 was satisfactory, except for the piston coretop which was lost. For this reason the records of the trigger-weight cores were combined with those of the piston cores. Considering the high rates of sedimentation recorded from the Red Sea (Ku et al., 1969) the cores were sampled at 10--20 cm intervals by extracting 10 cm s plugs. Samples were washed with water over standard sieves to obtain fractions <63, 63--149, and >149/~m, and oven-dried at 50°C. For coccolith studies the <63-pro fraction was centrifuged with water at 2500 rpm for 45 s. A portion of the deposit was agitated with water and allowed to settle for 5 minutes. A few drops were then placed on an SEM stub and dried before viewing. At least 300 specimens per sample were counted and studied for species identification and morphological observation. The > 149-pm fraction was randomly split and between 200 and 500 specimens of foraminifera and pteropods each were identified and counted. DISCUSSION The 61sO curves in the open ocean in the Gulf of Aden and the Red Sea are very similar, suggesting the isotopic composition of sea water as the major factor determining them. However, the global signal is amplified in the Red Sea because of strait dynamics at lowered sea level (Klinker et al., 1976; Reiss et al., 1980). The difference in ~110 in planktonic foraminifera and pteropod shells between the LGM and the present is about 1.5°/0o in the open ocean (Sarin and Hsueh-Wen, 1981), 20/00 in the Gulf of Aden (Deuser et al., 1976), and in excess of 5%0 in the Red Sea and the Gulf of Aqaba (Deuser et al., 1976; Reiss et al., 1980). It is unlikely that this latter great
M19
difference can be attributed to significant temperature changes, considering the low-latitude position of the Red Sea (CLIMAP Project Members, 1976). In addition, throughout the core sequences studied from the Gulf of Aqaba, evidence suggests that the minimum temperatures of all the fauna and flora present, especially the known winter isotherms of displaced shallow water, symbiont-bearing benthic foraminifera, did not drop below 17°C. Taking into account that the Gulf of Aqaba is well mixed throughout the year (no thermocline is present except for a short period of slight stratification) and that minimum Gulf temperature is 21°C, the greatest temperature difference between glacials and interglacials in the upper waters most likely did not exceed 4°C. Thus, of the 50/00 81sO glacial--interglacial difference, 1.5°/00 can be explained by global ice volume (Shackleton, 1977) and 1.0°/00 by the 4°C change in temperature (Dansgaard, 1964). This leaves 2.50/00 ~ 180 which is correlatable with an increase of about 10%0 salinity (Craig, 1966). Thus, the salinity of the Gulf probably rose to more than 500/00 during the LGM (Reiss et al., 1980). This extremely high salinity appears to be the cause for the total absence of planktonic foraminifera and coccolithophorids in strata corresponding to the LGM. Considering the abundance of aragonitic pteropods in the same strata, preservation cannot be invoked to explain the absence of low-Mg calcite shells. The large AS laO difference in the benthonic to planktonic foraminiferal ratio has been interpreted to represent increased stratification prior to the LGM (Winter, 1983). Nevertheless, the influence of stratification on the planktonic assemblages present should have been minimal as all planktonic species in the Gulf are epi- and shallow mesopelagic species (Reiss et al., 1980). Temperature seems also not to have been a critical factor since the temperature ranges of the species studies in the Gulf are wide, lying between 14 ° and 30°C (Halicz and Reiss, 1981; Almogi-Labin, 1982; Winter, 1983). Other factors such as food supply have been shown to influence the a~semblage composition of the groups mentioned here throughout the late Quaternary. However, there is no evidence that nutrients diminished to such an extent as to cause total disappearance of the planktonic groups studied. On the contrary, productivity seems to have increased during glacials (see the next section). The extremely rapid change in salinity prior to the LGM leads to the conclusion that salinity was the deciding factor dictating the extinction sequence of the various taxa shown in Fig. 1 and outlined below. Pteropods
Among the calcareous plankton this seems to be the most salinity tolerant group, the genus Creseis being particularly well adapted to high saiinities. C. acicula is the only species studied apparently able to withstand salinities of more than 500/00 (Almogi-Labin, 1982). This species lives today in hyper-saline lagoons with salinities above 450/00 (B~ and Gflmer, 1977). The number of specimens of C. acicula in sediments deposited during the LGM
M20
a~
.
.
~
,,,~,
=,,, .
uf'alxnqD / u p q / ~ •
..-~ o~
-r~
z~q/uoeoop¢doooHqd~cj
~e J~]/]nOOOS S~p OUl2c3~'~/O/~
~..
2~
0
0
~.£
k ~eqn~ sep/ou/~aZ~/qo/~
g,,
~e z~
~ ~,' ~.~.~ ~
Oln~.//~' ~'/~a.~0 • --
k
ao ~=r
0
.0
~
'-',
~.£
~g
o
~N
#. O
.= "IV13V-19 - J.SOd
~ • ~_
4.a
~
~.~_
~ ~ 0
._
O~ ~ C ~ •
4.~
m ~ ~.~ ~ •
M21
in the Aqaba cores is extremely low, indicating that 50o/o0 salinityis approximately the upper tolerance limit for this species. L o w counts of C. acicula cannot be explained by increased terrigenous input or decreased productivity: in fact,relativelylower sedimentation rates during glacialswere determined in the Aqaba cores, while considerations of fossilassemblages (including large diatom floras in the northern Red Sea) indicate heightened productivity of the upper water (Reiss et al.,1980; Halicz and Reiss, 1981; AlmogiLabin, 1982). Creseis virgula and Limacina trochiformis are apparently unable to survive the extreme salinitiesof the L G M , but were abundant during the higher than present glacialsalinities,prior to the L G M . However, L. trochiformis disappears before C. virgula and thus has an apparently lower salinitythreshold. These lattertwo species have been interpreted earlier from Red Sea cores as reflectingtransitionalconditions between normal and highly saline waters (Almogi-Labin, 1982).
Foraminifera No planktonic foraminifera have been found in the Aqaba sediments of the LGM, although benthonic species, especially Miliolidae, are abundant. This latter group, although widely distributed, is known to be c o m m o n in high-salinity environments (such as Persian Gulf lagoons) and in hypersaline mangroves and sebkhas of the Gulf of Aqaba (HaUcz and Reiss, 1981). Among the groups studied, planktonic foraminifera seem to be the least tolerant of high salinities. Only one species, Globigerinoides ruber, is present during the high-salinity conditions prior to the LGM, but it disappears rather early, and immediately after G. saccultfer, with rising salinity. Laboratory experiments carried out on living Globigerinoides saccuUfer from the Gulf of Aqaba, point to an upper tolerance limit of less than 500/00 for this species (Erez, in prep.). This may be, in fact, the upper salinity limit for all planktonic foraminifera.
Coccolithophorids The coccolithophorids living at present in the Gulf of Aqaba and occurring in the cores seem to be well adapted to high salinities. However, no species is able to survive the extreme salinities of the LGM. EmiUania huxleyi was considered up to now to be the most euryhaline species. However, it disappears before Gephyrocapsa oceanica which appears to be more tolerant of high salinities than E. huxleyi. It is noteworthy that in laboratory cultures E. huxleyi was unable to grow in salinities above 450/00 (Mjaaland, 1956). The upper salinity limit of E. huxleyi may be assumed to lie between 41 and 45%0, while that of G. oceanica should lie between 45 and 50o/00. CONCLUSION
This report demonstrates h o w biogenic constituents of marine sediments from ancient highly saline environments, for which no modern analogue
M22 exists, can be used t o deduce uppe r salinity tolerance limits of three different biological groups. Amo n g the coccolithophorids, Gephyrocapsa oceanica seems t o be the only species able t o live in salinities o f a b o u t 50°/00, planktonic foraminifera are apparently unable t o survive salinities o f m ore than a b o u t 48%0, while benthonic foraminifera, especially Mfliolidae, are able t o withstand salinities o f m or e than 50°/oo. Creseis acicula is the only p t e r o p o d (and calcareous planktonic species) surviving salinities of m ore than 50O/oo. ACKNOWLEDGEMENTS S u p p o r ted in part by U.S.A./Israel BSF Grant No. 1 7 6 2 / 7 8 to Z. Reiss, by NSF Gr an t OCE 7 6 8 1 4 8 8 t o Woods Hole Oceanographic Institution, Grant 0 1 5 . 7 1 3 8 (to Z. Reiss) o f the Israel Ministry o f Energy and Intrastructure and by a L ady Davis Fellowship t o A. Winter.
REFERENCES
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