What is a Lessepsian Migrant?
89
Canal. The same may be true for some bryozoans. The wood-boring amphipod
Chelura terebrans has to be considered among the passively transported fouling
organisms which do not need the special opportunity provided by the Suez Canal
in order to spread to the limits of their environmental tolerance.
Accidental Expatriates. The two species reported by Babic (1911) from the
port of Fiume (Rijeka) and collected there in 1896 (the swimming crab N eptunus
sanguinolentus and the rock lobster 7henus orientalis) evidently reached the port
through accidental transport. The finding of one specimen of the Red Sea fish
Abudefduf saxatilis in the Gulf of Naples (Tardent, 1959) may be included in the
same category. In molluscs the possibility of the transportation of shells by man
for cultural purposes has to be kept in mind. Haas (1948) found an empty shell of
the cowrie Monetaria mon eta near Acre and admits to the possibility that it served
to decorate the harness of a horse or a camel.
Errors and Incomplete Identifications. The pencil urchin H eterocentrotus mammillatus has been reported by Gauthier (1874) and Carus (1893) as "being in the
process of invading the Mediterranean". No tangible proof for this finding was
ever produced and it has to be considered as due to erroneous locality indication.
Pesta (1918) reports the finding of a specimen of the deepsea Platymaia wywillethompsoni from the Dalmatian port of Kotor in the Museum of Vienna. W. Steinitz
(1929) suggests that there was amistake in the museum label. According to
Holthuis (1956) the report of Porcellana boscii in the Mediterranean is based on a
misidentification. Peres (1967) lists the cirripede Tetraclita sp. among the Lessepsian migrants, however, I could not find the reference for this finding, nor a final
identification.
A last example is Haas (1942) who reported a benthic comb jelly Coeloplana
sp. from the Mediterranean coast of Israel. The genus is still considered an exclusively Indo-Pacific genus. However this unidentified ctenophore of the Mediterranean should not be considered as a Lessepsian migrant only on this ground.
In all the above-mentioned categories, true Lessepsian migrants might eventually be found. This is especially the case for the circumtropical and circumafrican
species. Some of these might actually be absent from the Eastern Mediterranean
or the Northern Red Sea and might have used the Suez Canal for their present
distribution. In other cases, a circumtropical species might be found to have
subspecifically segregated populations at both ends of the Canal; a more detailed
study of such a species may prove in the future that one of the subspecies has
actually invaded the area of another.
The restricted number of evident and demonstrable Lessepsian migrants is
therefore the result of a very careful selection (see Table 2). It is reasonable to
assurne that some of the more dubious cases-listed separately (Table 3)-are
also true Lessepsian migrants. Finally one has to take into account that a thorough investigation of areas and taxa insufficiently studied will probably treble the
number of actually known cases.
In the following list of evident migrants three categories have been included
representing different degrees of a high probability of migration.
1. Species known from the Red Sea, and from the Suez Canal, and known to
have spread along the Mediterranean coasts.
89
Canal. The same may be true for some bryozoans. The wood-boring amphipod
Chelura terebrans has to be considered among the passively transported fouling
organisms which do not need the special opportunity provided by the Suez Canal
in order to spread to the limits of their environmental tolerance.
Accidental Expatriates. The two species reported by Babic (1911) from the
port of Fiume (Rijeka) and collected there in 1896 (the swimming crab N eptunus
sanguinolentus and the rock lobster 7henus orientalis) evidently reached the port
through accidental transport. The finding of one specimen of the Red Sea fish
Abudefduf saxatilis in the Gulf of Naples (Tardent, 1959) may be included in the
same category. In molluscs the possibility of the transportation of shells by man
for cultural purposes has to be kept in mind. Haas (1948) found an empty shell of
the cowrie Monetaria mon eta near Acre and admits to the possibility that it served
to decorate the harness of a horse or a camel.
Errors and Incomplete Identifications. The pencil urchin H eterocentrotus mammillatus has been reported by Gauthier (1874) and Carus (1893) as "being in the
process of invading the Mediterranean". No tangible proof for this finding was
ever produced and it has to be considered as due to erroneous locality indication.
Pesta (1918) reports the finding of a specimen of the deepsea Platymaia wywillethompsoni from the Dalmatian port of Kotor in the Museum of Vienna. W. Steinitz
(1929) suggests that there was amistake in the museum label. According to
Holthuis (1956) the report of Porcellana boscii in the Mediterranean is based on a
misidentification. Peres (1967) lists the cirripede Tetraclita sp. among the Lessepsian migrants, however, I could not find the reference for this finding, nor a final
identification.
A last example is Haas (1942) who reported a benthic comb jelly Coeloplana
sp. from the Mediterranean coast of Israel. The genus is still considered an exclusively Indo-Pacific genus. However this unidentified ctenophore of the Mediterranean should not be considered as a Lessepsian migrant only on this ground.
In all the above-mentioned categories, true Lessepsian migrants might eventually be found. This is especially the case for the circumtropical and circumafrican
species. Some of these might actually be absent from the Eastern Mediterranean
or the Northern Red Sea and might have used the Suez Canal for their present
distribution. In other cases, a circumtropical species might be found to have
subspecifically segregated populations at both ends of the Canal; a more detailed
study of such a species may prove in the future that one of the subspecies has
actually invaded the area of another.
The restricted number of evident and demonstrable Lessepsian migrants is
therefore the result of a very careful selection (see Table 2). It is reasonable to
assurne that some of the more dubious cases-listed separately (Table 3)-are
also true Lessepsian migrants. Finally one has to take into account that a thorough investigation of areas and taxa insufficiently studied will probably treble the
number of actually known cases.
In the following list of evident migrants three categories have been included
representing different degrees of a high probability of migration.
1. Species known from the Red Sea, and from the Suez Canal, and known to
have spread along the Mediterranean coasts.