2
Conspectus
3. A Preamble to the Conclusions
The structure of the book as exposed above takes a somewhat meandering
course and might therefore impose some difficulty on the less patient reader who
is interested chiefly in grasping the conclusions of the work. We therefore give
here a brief summary of the conclusions.
1. The separation ofthe Atlantic biota from the Indo-Pacific biota is as old as
the late Miocene, and the significance of Lessepsian migration as a contact established after some ten millions of years is accordingly great.
2. The key to an understanding of Lessepsian migration lies in the analysis of
the Pleistocene adaptations ofthe Red Sea and Mediterranean biota, the environmental conditions of the Suez Canal, primarily those of the Bitter Lakes and Lake
Timsah, and also the diversity ofthe Eastern Mediterranean biota as a function of
the present environmental conditions ofthis sea.
3. The Suez Canal is, generaHy speaking, a metahaline-marine environment.
Its biota has reached, during its hundred years' existence, a certain successional
maturity with a high level of diversity. The Lessepsian migrants are, as a rule,
recruited from among the Suez Canal biota.
4. The Lessepsian migrants, assumed to number around 500 species, ofwhich
over 200 are listed, are presently concentrated along the Levant Coasts. Fishes
~lDd decapod crustaceans, as weH as a few moHuscs, have advanced beyond the
limits of the Levant Basin.
5. There are no signs of invasional population patterns (i.e. rapid build-up
and then population crash), but rather of a gradual increase and advance as
against an accommodation or withdrawal of local competing species. No evolutionary changes of discernible dimensions are to be found as yet among the new
settlers.
6. There is no indication that Lessepsian migration is speeding up. It seems,
rather, that the process tends to an asymptotic equilibrium. The effects of the
cessation of the Nile flow are as yet uncertain. In the present geoclimatic episode
the Lessepsian migrants are limited to the Levant Basin and the North African
gulfs.
7. Lessepsian migration is more similar to the postglacial faunal interchanges
between the mediterranean sill-limited, seas than to the faunal movements (or lack
ofmovements) through other existing interoceanic shipping canals.
The reader who expects to find an analysis of Lessepsian migration along the
lines of modem quantitative ecology will be disappointed. The dimensions of the
phenomenon and the lack of uniformity of the available data are such as to make
attempts of this kind impossible. Applying new research methods to Les~epsian
migration will no doubt result in new insights in the future. But years will pass
before sufficient specific cases from different taxa have been investigated; meanwhile, the existing data should be fuHy exploited to provide some working hypotheses for a process which commencedjust over one century ago.
Conspectus
3. A Preamble to the Conclusions
The structure of the book as exposed above takes a somewhat meandering
course and might therefore impose some difficulty on the less patient reader who
is interested chiefly in grasping the conclusions of the work. We therefore give
here a brief summary of the conclusions.
1. The separation ofthe Atlantic biota from the Indo-Pacific biota is as old as
the late Miocene, and the significance of Lessepsian migration as a contact established after some ten millions of years is accordingly great.
2. The key to an understanding of Lessepsian migration lies in the analysis of
the Pleistocene adaptations ofthe Red Sea and Mediterranean biota, the environmental conditions of the Suez Canal, primarily those of the Bitter Lakes and Lake
Timsah, and also the diversity ofthe Eastern Mediterranean biota as a function of
the present environmental conditions ofthis sea.
3. The Suez Canal is, generaHy speaking, a metahaline-marine environment.
Its biota has reached, during its hundred years' existence, a certain successional
maturity with a high level of diversity. The Lessepsian migrants are, as a rule,
recruited from among the Suez Canal biota.
4. The Lessepsian migrants, assumed to number around 500 species, ofwhich
over 200 are listed, are presently concentrated along the Levant Coasts. Fishes
~lDd decapod crustaceans, as weH as a few moHuscs, have advanced beyond the
limits of the Levant Basin.
5. There are no signs of invasional population patterns (i.e. rapid build-up
and then population crash), but rather of a gradual increase and advance as
against an accommodation or withdrawal of local competing species. No evolutionary changes of discernible dimensions are to be found as yet among the new
settlers.
6. There is no indication that Lessepsian migration is speeding up. It seems,
rather, that the process tends to an asymptotic equilibrium. The effects of the
cessation of the Nile flow are as yet uncertain. In the present geoclimatic episode
the Lessepsian migrants are limited to the Levant Basin and the North African
gulfs.
7. Lessepsian migration is more similar to the postglacial faunal interchanges
between the mediterranean sill-limited, seas than to the faunal movements (or lack
ofmovements) through other existing interoceanic shipping canals.
The reader who expects to find an analysis of Lessepsian migration along the
lines of modem quantitative ecology will be disappointed. The dimensions of the
phenomenon and the lack of uniformity of the available data are such as to make
attempts of this kind impossible. Applying new research methods to Les~epsian
migration will no doubt result in new insights in the future. But years will pass
before sufficient specific cases from different taxa have been investigated; meanwhile, the existing data should be fuHy exploited to provide some working hypotheses for a process which commencedjust over one century ago.