The Analysis ofLessepsian Migration-Methodology
127
The influence of the Nile flood was also feIt in its biological consequences.
Gorgy (1966) measured a very high value of P04. phosphate: 1.76 J.lg/l at 30 m
depth in October 1959 in the Gulf ofPelusium (Tina). This was accompanied by a
water bloom of planktonic algae reaching a maximum of 3,120,000 cells/l. In
March 1959 the phosphate levels were low (maximum 0.11 J.lg/l) and the maximum photoplankton counts were only 8100 cells/l.
Phytoplankton blooms accompanying the Nile waters were also observed by
Liebman (1935) off Haifa. Komarovsky (1953), Halim (1960), and Halim et al.
(1967) listed the diatom species responsible for the Nile blooms, and the ftrst
author indicated the c1adoceran Podon polyphemoides as typical of the September
plankton. The main pelagic commercial ftsh of the Levant Basin, Sardinella aurita concentrated preferentially in the offshore area of the Nile Delta during the
flood and bloom period.
There is no evidence of negative influence of the Nile flood on the Lessepsian
migration. After all, the species advancing northward through the canal had
already encountered low salinities of ± 38%0 in Lake Timsah, and the low values
to the east of Port Said were restricted to two months, September-October at
most, and concerned only the topmost 5 m of water column. West of Port Said,
where the Nile flood could dilute the inshore areas till February-March, the "low
salinity" barrier was most probably a more effective one.
The Nile was hermetically dammed behind the Aswan High Dam in 1965. All
the above-mentioned seasonal phenomena have ceased since, and since that date
hardly a drop of Nile water has reached the Mediterranean. For reasons explained above no short-term influence on the eastward migration of the Lessepsian migrants is expected. However, the westward migration along the African
shore may be facilitated, as shown previously (Por, 1971 b).
In the long run, the shoreline of the southern Levant coast is expected to be
gradually eroded, since the sediment supply has been cut off. The Sirbonic Lagoon may become an open gulf in the not too far future. However, even before
that, a slow increase in the salinity of the Levant Basin will presumably follow.
With an annual evaporation of 1300-1500 cm/year the loss of the Nile waters will
start to be feIt. A more saline Levant Basin will eventually be more favorable to
the Lessepsian migrants-provided temperatures do not decrease. Oren (1969)
expects a slight increase in the primary production due to the disappearing seasonal saline stratiftcation of the Levant inshore waters. However, these forecasts
will be discussed in further detail in the conc1uding Chapters 3.7 and 3.11.
3.4 Tbe Analysis of Lessepsian Migration-Methodology
The two lists of Lessepsian migrants contain a total of 204 species 1, of which
128 are considered as High Probability Lessepsian Migrants (HPLM) and 76 as
Low Probability Lessepsian Migrants (LPLM). The few cases of parasites reported till now as having migrated together with their hosts are not inc1uded in
these lists.
1 New additions while this manuscript was in preparation are the fishes Rhonciscus stridens
and Gobius ? lesueuri (Ben Tuvia personal communication).
127
The influence of the Nile flood was also feIt in its biological consequences.
Gorgy (1966) measured a very high value of P04. phosphate: 1.76 J.lg/l at 30 m
depth in October 1959 in the Gulf ofPelusium (Tina). This was accompanied by a
water bloom of planktonic algae reaching a maximum of 3,120,000 cells/l. In
March 1959 the phosphate levels were low (maximum 0.11 J.lg/l) and the maximum photoplankton counts were only 8100 cells/l.
Phytoplankton blooms accompanying the Nile waters were also observed by
Liebman (1935) off Haifa. Komarovsky (1953), Halim (1960), and Halim et al.
(1967) listed the diatom species responsible for the Nile blooms, and the ftrst
author indicated the c1adoceran Podon polyphemoides as typical of the September
plankton. The main pelagic commercial ftsh of the Levant Basin, Sardinella aurita concentrated preferentially in the offshore area of the Nile Delta during the
flood and bloom period.
There is no evidence of negative influence of the Nile flood on the Lessepsian
migration. After all, the species advancing northward through the canal had
already encountered low salinities of ± 38%0 in Lake Timsah, and the low values
to the east of Port Said were restricted to two months, September-October at
most, and concerned only the topmost 5 m of water column. West of Port Said,
where the Nile flood could dilute the inshore areas till February-March, the "low
salinity" barrier was most probably a more effective one.
The Nile was hermetically dammed behind the Aswan High Dam in 1965. All
the above-mentioned seasonal phenomena have ceased since, and since that date
hardly a drop of Nile water has reached the Mediterranean. For reasons explained above no short-term influence on the eastward migration of the Lessepsian migrants is expected. However, the westward migration along the African
shore may be facilitated, as shown previously (Por, 1971 b).
In the long run, the shoreline of the southern Levant coast is expected to be
gradually eroded, since the sediment supply has been cut off. The Sirbonic Lagoon may become an open gulf in the not too far future. However, even before
that, a slow increase in the salinity of the Levant Basin will presumably follow.
With an annual evaporation of 1300-1500 cm/year the loss of the Nile waters will
start to be feIt. A more saline Levant Basin will eventually be more favorable to
the Lessepsian migrants-provided temperatures do not decrease. Oren (1969)
expects a slight increase in the primary production due to the disappearing seasonal saline stratiftcation of the Levant inshore waters. However, these forecasts
will be discussed in further detail in the conc1uding Chapters 3.7 and 3.11.
3.4 Tbe Analysis of Lessepsian Migration-Methodology
The two lists of Lessepsian migrants contain a total of 204 species 1, of which
128 are considered as High Probability Lessepsian Migrants (HPLM) and 76 as
Low Probability Lessepsian Migrants (LPLM). The few cases of parasites reported till now as having migrated together with their hosts are not inc1uded in
these lists.
1 New additions while this manuscript was in preparation are the fishes Rhonciscus stridens
and Gobius ? lesueuri (Ben Tuvia personal communication).