156
The Migrant Biota
Assuming that drastic climatic fluctuations are bound to continue, the Lessepsian newcomers must be seen as additional actors on the Pleistocene Mediterranean scene. They will expand further west if the climate warms up further, or
retreat east and south and eventually disappear if the cold climate returns. Some
species ofLessepsian migrant molluscs, especially Cerithium kochi, Cerithium scabridum, Murex tribulus, Thais carinifera, Pinctada radiata, Brachidontes variabilis,
M alleus regula, and Paphia textile, will remain the indicator fossils of the "Lessepsian" facies in the Eastern Mediterranean palaeontology of the future.
In the present human-scale historical per iod one has to consider that the
Lessepsian influence will remain confined to the Eastern Mediterranean with the
above-mentioned exceptions of the Aegean and the Adriatic. However, there are
changes bound to occur within the coming years. Much has been written concerning the infl uence of the Aswan High Dam on the process of Lessepsian migration.
Some authors have gone as far as to ass urne that the further depletion of nutrients
in the already nutrient-poor Levant Sea (as a result of the cessation of the Nile
influx) will in some undefined way add further advantages to the invading Lessepsian migrant species. As noted above, there are indications that after the influx of
Lessepsian migrants, better use, or rather additional use is being made of some
trophic niches of the Levant coast. However, this is occurring without changing
the general trophic framework ofthe sea.
A considerable contingent of Red Sea organisms are provided with endosymbiotic algae, especially dinoflagellates, and blue-green algae. The coral reefs with
their endosymbiontic zooxanthellae are the product of a successful adaptation to
a nutrient-poor environment. The zooplankton of the Indian Ocean and the Red
Sea-particularly Radiolaria, Foraminifera and even Dinoflagellata-provide
their own intracellular nutrient-photosynthetic system through symbiotic zooxanthellae or cyanellae. Taylor (1973) considers that: "the blue-green partners of
dynophisoid dinoflagellates are nitrogen ftxers as well as carbon ftxers" and that:
"Such an attribute would be of great value in the Indian Ocean where nitrogendepleted conditions seem to be much more frequent than phosphorus depletion ... " Reiss (personal communication) studying the globigerinid foraminiferans
of the Gulf of Elat also dwells at length on the endosymbiotic nutrition of these
planktonic forms. Khmeleva (1967) even thinks that in the Red Sea the roIe of the
radiolaria-zooxanthellae system is more important in terms of primary production than the role of the free-living phytoplankton.
Besides reef and plankton organisms, several other inshore invertebrates, such
as the giant c1am Tridacna, the benthic medusa Cassiopea, and perhaps also
ascidians and sponges supplement their food by endosymbiontic zooxanthellae. lt
is important to point out that none of the endosymbiont-harboring Red Sea
species appears in the list of Lessepsian migrants. One can only speculate on the
reason for this absence; it may be ftrst of all connected with the stenohalinity of
these organisms, or with the requirement for high temperatures. It is also possible
that the relation between host and al ga is secondarily disturbed by a physiological
effect of salinity and temperature variations. It is interesting that Cassiopea andromeda-a very hardy and euryhaline species, which long aga succeeded in
colonizing the Canal-did not advance into the Mediterranean. It will be worth-
The Migrant Biota
Assuming that drastic climatic fluctuations are bound to continue, the Lessepsian newcomers must be seen as additional actors on the Pleistocene Mediterranean scene. They will expand further west if the climate warms up further, or
retreat east and south and eventually disappear if the cold climate returns. Some
species ofLessepsian migrant molluscs, especially Cerithium kochi, Cerithium scabridum, Murex tribulus, Thais carinifera, Pinctada radiata, Brachidontes variabilis,
M alleus regula, and Paphia textile, will remain the indicator fossils of the "Lessepsian" facies in the Eastern Mediterranean palaeontology of the future.
In the present human-scale historical per iod one has to consider that the
Lessepsian influence will remain confined to the Eastern Mediterranean with the
above-mentioned exceptions of the Aegean and the Adriatic. However, there are
changes bound to occur within the coming years. Much has been written concerning the infl uence of the Aswan High Dam on the process of Lessepsian migration.
Some authors have gone as far as to ass urne that the further depletion of nutrients
in the already nutrient-poor Levant Sea (as a result of the cessation of the Nile
influx) will in some undefined way add further advantages to the invading Lessepsian migrant species. As noted above, there are indications that after the influx of
Lessepsian migrants, better use, or rather additional use is being made of some
trophic niches of the Levant coast. However, this is occurring without changing
the general trophic framework ofthe sea.
A considerable contingent of Red Sea organisms are provided with endosymbiotic algae, especially dinoflagellates, and blue-green algae. The coral reefs with
their endosymbiontic zooxanthellae are the product of a successful adaptation to
a nutrient-poor environment. The zooplankton of the Indian Ocean and the Red
Sea-particularly Radiolaria, Foraminifera and even Dinoflagellata-provide
their own intracellular nutrient-photosynthetic system through symbiotic zooxanthellae or cyanellae. Taylor (1973) considers that: "the blue-green partners of
dynophisoid dinoflagellates are nitrogen ftxers as well as carbon ftxers" and that:
"Such an attribute would be of great value in the Indian Ocean where nitrogendepleted conditions seem to be much more frequent than phosphorus depletion ... " Reiss (personal communication) studying the globigerinid foraminiferans
of the Gulf of Elat also dwells at length on the endosymbiotic nutrition of these
planktonic forms. Khmeleva (1967) even thinks that in the Red Sea the roIe of the
radiolaria-zooxanthellae system is more important in terms of primary production than the role of the free-living phytoplankton.
Besides reef and plankton organisms, several other inshore invertebrates, such
as the giant c1am Tridacna, the benthic medusa Cassiopea, and perhaps also
ascidians and sponges supplement their food by endosymbiontic zooxanthellae. lt
is important to point out that none of the endosymbiont-harboring Red Sea
species appears in the list of Lessepsian migrants. One can only speculate on the
reason for this absence; it may be ftrst of all connected with the stenohalinity of
these organisms, or with the requirement for high temperatures. It is also possible
that the relation between host and al ga is secondarily disturbed by a physiological
effect of salinity and temperature variations. It is interesting that Cassiopea andromeda-a very hardy and euryhaline species, which long aga succeeded in
colonizing the Canal-did not advance into the Mediterranean. It will be worth-