Analysis of the Colonizing Success of Lessepsian Migrants
141
and P.polymorphus (paperna, 1972d). On the other hand Crenidens erenidens the
lagoon-dwelling fish has a different parasitofauna in the Mediterranean lagoons
compared with those of the Red Sea. In the lagoons it shares the monogenean
Lamellodiscus elegans with the Mediterranean fish Diplodus sargus and the same
trematode species with the Mediterranean Sparus aurata. The euryhaline Mediterranean fish Dicentrarchus punctatus recently reported from the EI Bilaiyim
lagoon in the Gulf of Suez has a rather different parasitic fauna (paperna, 1974).
One may surmise, on grounds of comparative parasitology, that the two euryhaline fishes may have migrated in their opposite ways in pre-Lessepsian times,
through estuarine, isthmian connections; they therefore had time to change their
original parasitofauna. Some Lessepsian migrants, e.g. H emiramphus Jar and
Sphyraena chrysotaenia do not carry a Red Sea parasito fauna in their new Mediterranean habitat.
Paperna and Overstreet (in press) consider that some parasites of Mugil in the
Mediterranean, such as the monogeneans Benedenia n. sp. and the copepod Nipergasilus bora may be regarded as Indo-Pacific irnmigrants. On the contrary, the
acanthocephalan N eoechinorh ynchus agilis and the copepod Pseudocaligus apodus may have migrated together with the mullets into the Red Sea.
It is c1ear that several species of parasites have to be added to the list of the
Lessepsian migrants and possibly also to the "Anti-Lessepsians" (i.e. migrants to
the Red Sea). These are evidently species which are at least as euryhaline as their
hosts.
There is no sense to complain again on the lack of further information in this
interesting field of study. Suffice it to quote from Paperna (1972d) a questioning
sentence which still needs an answer: "If immigrant species are like1y to be re1atively less infected with parasites and pathogens, will they eventually become
more competitive and eventually overtake the local species?"
3.7 Analysis of the Colonizing Success
of Lessepsian Migrants
Very litde has been done to understand the reason for the success of the
Lessepsian migrants. We have no adequate monitoring of the buildup of the
migrant populations, of their dependence on the environmental factors, and of
their interactions with the autochthonous biota.
In most cases we are confined to occasional collecting data, from scattered
localities. In very few cases have the findings been rechecked in the same locality.
This accidental character of our knowledge-evident at the qualitative level discussed above-becomes more painfully feIt if we try to reach quantitative, dynamic or ecological conc1usions.
One circumstance is neverthe1ess c1ear and beyond doubt: the Lessepsian
migrants are successful species, expansive r strategists (Pianka, 1970) and there are
no known examples of a reversal-i.e. of a disappearance or radical depletion of
the Lessepsian population in the Mediterranean. In the words of Gilat (1969):
"Wehave evidence that all the imrnigrants became members of the existing
141
and P.polymorphus (paperna, 1972d). On the other hand Crenidens erenidens the
lagoon-dwelling fish has a different parasitofauna in the Mediterranean lagoons
compared with those of the Red Sea. In the lagoons it shares the monogenean
Lamellodiscus elegans with the Mediterranean fish Diplodus sargus and the same
trematode species with the Mediterranean Sparus aurata. The euryhaline Mediterranean fish Dicentrarchus punctatus recently reported from the EI Bilaiyim
lagoon in the Gulf of Suez has a rather different parasitic fauna (paperna, 1974).
One may surmise, on grounds of comparative parasitology, that the two euryhaline fishes may have migrated in their opposite ways in pre-Lessepsian times,
through estuarine, isthmian connections; they therefore had time to change their
original parasitofauna. Some Lessepsian migrants, e.g. H emiramphus Jar and
Sphyraena chrysotaenia do not carry a Red Sea parasito fauna in their new Mediterranean habitat.
Paperna and Overstreet (in press) consider that some parasites of Mugil in the
Mediterranean, such as the monogeneans Benedenia n. sp. and the copepod Nipergasilus bora may be regarded as Indo-Pacific irnmigrants. On the contrary, the
acanthocephalan N eoechinorh ynchus agilis and the copepod Pseudocaligus apodus may have migrated together with the mullets into the Red Sea.
It is c1ear that several species of parasites have to be added to the list of the
Lessepsian migrants and possibly also to the "Anti-Lessepsians" (i.e. migrants to
the Red Sea). These are evidently species which are at least as euryhaline as their
hosts.
There is no sense to complain again on the lack of further information in this
interesting field of study. Suffice it to quote from Paperna (1972d) a questioning
sentence which still needs an answer: "If immigrant species are like1y to be re1atively less infected with parasites and pathogens, will they eventually become
more competitive and eventually overtake the local species?"
3.7 Analysis of the Colonizing Success
of Lessepsian Migrants
Very litde has been done to understand the reason for the success of the
Lessepsian migrants. We have no adequate monitoring of the buildup of the
migrant populations, of their dependence on the environmental factors, and of
their interactions with the autochthonous biota.
In most cases we are confined to occasional collecting data, from scattered
localities. In very few cases have the findings been rechecked in the same locality.
This accidental character of our knowledge-evident at the qualitative level discussed above-becomes more painfully feIt if we try to reach quantitative, dynamic or ecological conc1usions.
One circumstance is neverthe1ess c1ear and beyond doubt: the Lessepsian
migrants are successful species, expansive r strategists (Pianka, 1970) and there are
no known examples of a reversal-i.e. of a disappearance or radical depletion of
the Lessepsian population in the Mediterranean. In the words of Gilat (1969):
"Wehave evidence that all the imrnigrants became members of the existing