The Model of Lessepsian Migration and Other Inter-Oceanic Contacts
169
that "the free mixing of tropical American biotas would enact irreversible
changes, not only locally, but, eventually throughout the Indo-Pacific and the
tropical Atlantic ... some of these interactions are likely to be quite undesirable
and the potential threat as regards a sea-Ievel canal cannot be ignored" (Newman, 1972). Recognizing the priority of economic and other needs in building a
big sea-Ievel canal, CERIC asked that "it should be designed in such a way as to
minimalize ecological effects". The recommendation asked for establishment of
an "antibiotic barrier" through a combination of low salinity and high temperature, on the trajectory of the canal. The Canal Commission appointed by the
President of the United States did not take into consideration the fears and
recommendations of CERIC among others on the fundamentally wrong affirmation that "significant and rather extensive movement of marine life" had already
taken place through the present Canal! The Canal Commission went on and
decided that "the risk of adverse ecological consequences ... appears to be acceptable" and that no antibiotic barrier should be planned for, since "the need for
anything in addition to tidal gates has not been established".
Meanwhile, the construction of the Panama sea-Ievel canal has been shelved
for economic and also political reasons. However, sooner or later, the project will
come up again, and with it the basic discussion will be reopened.
The whole problem of the effects of a Central American sea-Ievel canal is a
matter of prevision, and the truth should be somewhere midway between the
pessimists and the "fearless" engineers. It is evident that a faunal interchange will
occur and it is inconceivable that anything should be left to chance if prophylaxis
is so simple.
What can be learned from the Lessepsian migration concerning any future
sea-Ievel canal?
1. The faunal movements will not follow invasional patterns with isolated
species playing the main role. The rule is the advance or readjustment of whole
biota or faunas.
2. The selection of the migratory biota will be the result of several factors:
(a) the hydrographic-edaphic conditions of the canal; (b) the hydrological and
edaphic conditions in the vicinity and around the canal outlets; (c) the Pleistocene-historical phase through which the newly connected seas go, i.e. the relation
between advancing and retreating biota in the two seas under the present climatic-oceanographical circumstances.
3. Despite the above statement, several taxa will be apriori excluded from
migration because of the environment typical to any type of canal. There will be
no migration of deep sea forms, of very stenohaline species (since the canal will be
either less or more saline than the sea, according to its climatological setting), of
holoplanktonic species, of species necessitating clean and wave-swept rocky bottoms.
4. There will be no extermination of the local concurrent species. These will
retreat either to the deep or more central parts of their areal, where indirect
competition through the abiotic environmental factor will hinder further advance
of the newcomers. With respect to commercial fisheries this readjustment may
'change yields and replace well-priced species with low-commercial-value species.
169
that "the free mixing of tropical American biotas would enact irreversible
changes, not only locally, but, eventually throughout the Indo-Pacific and the
tropical Atlantic ... some of these interactions are likely to be quite undesirable
and the potential threat as regards a sea-Ievel canal cannot be ignored" (Newman, 1972). Recognizing the priority of economic and other needs in building a
big sea-Ievel canal, CERIC asked that "it should be designed in such a way as to
minimalize ecological effects". The recommendation asked for establishment of
an "antibiotic barrier" through a combination of low salinity and high temperature, on the trajectory of the canal. The Canal Commission appointed by the
President of the United States did not take into consideration the fears and
recommendations of CERIC among others on the fundamentally wrong affirmation that "significant and rather extensive movement of marine life" had already
taken place through the present Canal! The Canal Commission went on and
decided that "the risk of adverse ecological consequences ... appears to be acceptable" and that no antibiotic barrier should be planned for, since "the need for
anything in addition to tidal gates has not been established".
Meanwhile, the construction of the Panama sea-Ievel canal has been shelved
for economic and also political reasons. However, sooner or later, the project will
come up again, and with it the basic discussion will be reopened.
The whole problem of the effects of a Central American sea-Ievel canal is a
matter of prevision, and the truth should be somewhere midway between the
pessimists and the "fearless" engineers. It is evident that a faunal interchange will
occur and it is inconceivable that anything should be left to chance if prophylaxis
is so simple.
What can be learned from the Lessepsian migration concerning any future
sea-Ievel canal?
1. The faunal movements will not follow invasional patterns with isolated
species playing the main role. The rule is the advance or readjustment of whole
biota or faunas.
2. The selection of the migratory biota will be the result of several factors:
(a) the hydrographic-edaphic conditions of the canal; (b) the hydrological and
edaphic conditions in the vicinity and around the canal outlets; (c) the Pleistocene-historical phase through which the newly connected seas go, i.e. the relation
between advancing and retreating biota in the two seas under the present climatic-oceanographical circumstances.
3. Despite the above statement, several taxa will be apriori excluded from
migration because of the environment typical to any type of canal. There will be
no migration of deep sea forms, of very stenohaline species (since the canal will be
either less or more saline than the sea, according to its climatological setting), of
holoplanktonic species, of species necessitating clean and wave-swept rocky bottoms.
4. There will be no extermination of the local concurrent species. These will
retreat either to the deep or more central parts of their areal, where indirect
competition through the abiotic environmental factor will hinder further advance
of the newcomers. With respect to commercial fisheries this readjustment may
'change yields and replace well-priced species with low-commercial-value species.