Time-Distance Analysis
131
Red Sea to counterbalance the number of species which had migrated into the
Mediterranean. A simpler explanation is that there is a limited stock of Suez
Canal species from which the migrants are recruited; the biota of the Canal has
reached a climax-like stability and, therefore, the migration as far as species
diversity is concerned, is approaching an end. This is a thesis already expressed by
me in previous papers (por, 1971 b, 1973c) and still upheld here.
2. The chronological difference between 3.0.0 and 0.3.0 is much shorter than
between the chronologica1ly earlier combinations. Eventually, only the 3.0.0 species managed to emerge from the Canal during the last decades.
There is no evidence for a presently increased rate of migration into the
Mediterranean as presumed by many authors. In the two fIrst periods (0.1.0 and
0.2.0) the increase is evident: 23 species as compared to 81, respectively. Between
the second the third period (0.2.0 and 0.3.0) the increase is much less dramatic, Le.
from 81 to 89 species. Combining this with the circumstance of considerably less
"new entries" into the Canal (i.e. 25 3.0.0 species) the impression of a general
slowing down of the process of Lessepsian migration becomes more apparent.
Nevertheless, it must be noted that the difference between 0.2.0 and 0.3.0 is
mainly due to the large number of 4.3.0 species, i.e. not reported from the Canal. If
one takes into account that the species which could cross the Canal quickly, in
"one jump", are among the 4.0.0 species, a tentative conclusion can be presented
that in the last years the "one jump" migration might have become somewhat
more important compared to the "step by step" process of migration. In this
connection it is of interest that among the latest additions to the Lessepsian
migrant fishes are Rastrelliger kanagurta and Scomberomorus commerson (two 4.3.2
species)-the fIrst cases of outright pelagic fIshes (sensu Ben-Tuvia, 1972) which
have crossed the Canal. Also the two pelagic diatoms, reported quite recently by
Kimor (personal communication), Chaetoceros coarctatus and Rhizosolenia indica, are the fIrst instances of Lessepsian migrants among phytoplanktonic organisms.
With regard to the localization of the Lessepsian migrants in the Mediterranean, several other facts become evident (Fig. 36). There are only 41 species out
of 193 (21.24%) which are 0.0.1 species, i. e. confIned to the vicinity of the Canal
outlet. It is clear that ifthe Egyptian coast is to be considered a "take-off area" for
the migrants, they obviously do not spend too much time there before moving
farther. One also has to take into account that this area is not too favorable as far
as substrate conditions are concerned. Some of the 0.0.1 species are euryhaline, for
which the Sirbonic lagoon or Lake Manzala are favorable environments. Another
group among these is that of the 10 epiphytic species of algae reported by Aleem
from the Egyptian and Sinai coasts. Some of the 0.0.1 species have been found
during the extensive benthic research by Steuer (1935) on the fishery grounds of
Alexandria.
The great majority of the Lessepsian migrants are found along the Levant
shores (0.0.2}-106 species have reached the Levant shore (54.92%). Among the
0.0.3 species are 31 other species which can be found on the Levant shore. The
0.0.4 area of North African shores has four species in common with 0.0.2. This
brings the number of Lessepsian migrants living along the shores of Israel-Lebanon-Syria to 141, or 71.21 % ofthe total.
131
Red Sea to counterbalance the number of species which had migrated into the
Mediterranean. A simpler explanation is that there is a limited stock of Suez
Canal species from which the migrants are recruited; the biota of the Canal has
reached a climax-like stability and, therefore, the migration as far as species
diversity is concerned, is approaching an end. This is a thesis already expressed by
me in previous papers (por, 1971 b, 1973c) and still upheld here.
2. The chronological difference between 3.0.0 and 0.3.0 is much shorter than
between the chronologica1ly earlier combinations. Eventually, only the 3.0.0 species managed to emerge from the Canal during the last decades.
There is no evidence for a presently increased rate of migration into the
Mediterranean as presumed by many authors. In the two fIrst periods (0.1.0 and
0.2.0) the increase is evident: 23 species as compared to 81, respectively. Between
the second the third period (0.2.0 and 0.3.0) the increase is much less dramatic, Le.
from 81 to 89 species. Combining this with the circumstance of considerably less
"new entries" into the Canal (i.e. 25 3.0.0 species) the impression of a general
slowing down of the process of Lessepsian migration becomes more apparent.
Nevertheless, it must be noted that the difference between 0.2.0 and 0.3.0 is
mainly due to the large number of 4.3.0 species, i.e. not reported from the Canal. If
one takes into account that the species which could cross the Canal quickly, in
"one jump", are among the 4.0.0 species, a tentative conclusion can be presented
that in the last years the "one jump" migration might have become somewhat
more important compared to the "step by step" process of migration. In this
connection it is of interest that among the latest additions to the Lessepsian
migrant fishes are Rastrelliger kanagurta and Scomberomorus commerson (two 4.3.2
species)-the fIrst cases of outright pelagic fIshes (sensu Ben-Tuvia, 1972) which
have crossed the Canal. Also the two pelagic diatoms, reported quite recently by
Kimor (personal communication), Chaetoceros coarctatus and Rhizosolenia indica, are the fIrst instances of Lessepsian migrants among phytoplanktonic organisms.
With regard to the localization of the Lessepsian migrants in the Mediterranean, several other facts become evident (Fig. 36). There are only 41 species out
of 193 (21.24%) which are 0.0.1 species, i. e. confIned to the vicinity of the Canal
outlet. It is clear that ifthe Egyptian coast is to be considered a "take-off area" for
the migrants, they obviously do not spend too much time there before moving
farther. One also has to take into account that this area is not too favorable as far
as substrate conditions are concerned. Some of the 0.0.1 species are euryhaline, for
which the Sirbonic lagoon or Lake Manzala are favorable environments. Another
group among these is that of the 10 epiphytic species of algae reported by Aleem
from the Egyptian and Sinai coasts. Some of the 0.0.1 species have been found
during the extensive benthic research by Steuer (1935) on the fishery grounds of
Alexandria.
The great majority of the Lessepsian migrants are found along the Levant
shores (0.0.2}-106 species have reached the Levant shore (54.92%). Among the
0.0.3 species are 31 other species which can be found on the Levant shore. The
0.0.4 area of North African shores has four species in common with 0.0.2. This
brings the number of Lessepsian migrants living along the shores of Israel-Lebanon-Syria to 141, or 71.21 % ofthe total.