140
The Migrant Biota
explain, for instance, why Cassiopea andromeda, the medusa which was so successful in colonizing the Canal, did not succeed in expanding into the Mediterranean.
The broad ecological valency of the Lessepsian migrants makes them very
successful in the intraspecific competition in their new environment. Therefore,
the biotic relationships established in the Mediterranean between the invaders
and the autochthones probably-within certain environmental limits-lead to
the success ofthe Lessepsian migrants.
Unlike some ofthe well-known invasional episodes ofterrestrial zoology, the
Lessepsian migration is a success story. The Lessepsian migrants are gradually
building up their populations and expanding within their new marine province. I
know of no case in which a Lessepsian migrant recorded at an early date disappeared afterwards. There are no reported cases of area restriction following the
primary expansion. There were no population explosions and population crashes.
Unfortunately, the process of colonization, of niche conquest, or of species
displacement has not been followed and studied even in one single Lessepsian
species. The few scattered and circumstantial data available in order to describe
the fate ofthe Lessepsian migrants within their new environments are compiled in
Chapter 3.7.
A highly significant subject for investigation reiated to Lessepsian migration
has only recently been approached: the study of the parasite fauna of the migrants
can be of importance in three very important respects: (1) comparative parasitology may give additional c1ues, confrrm or disprove zoogeographical conc1usions;
(2) it may explain the success of the migrant in its new environment; and (3) it
may indicate newly established interactions between local and newcomer species
and reveal a potential threat of epidemics.
Unfortunately, the only data available are those concerning ichthyoparasites,
and these data are provided exc1usively by the work done by Paperna and some of
his collaborators. In Paperna's words (1972d): "Parasites may be introduced by
migrant fish and consequently infect the autochthonous fish. The change in the
environment may increase the pathogenic effect of the parasites on their original
migrant host. The original parasitofauna of the migrant host may be lost altogether in the new environment."
Paperna (1972d) conc1udes that endoparasites cannot migrate unless their
intermediary hosts, i.e. invertebrate species, actually migrate together with the fish
species. Only the snail Pirenella cailliaudi which is known to harbor metacercariae of several species of helminths, might be a source for endoparasites alien to
the Mediterranean.
Ectoparasites migrate together with their hosts if they are euryhaline and
eurythermal enough. A "c1eaning" of the fish through migration into a more
saline environment has been documented by Paperna and Lahav (1975) for the
Mugil species ofthe Sirbonic lagoon (Bardawil).
The ectoparasitic monogenean Ancyrocephalus salinus has followed its host
Aphanius dispar everywhere: it is known from the Red Sea, the Mediterranean,
and also from the landlocked springs arol!lld the Dead Sea (paperna, 1964).
The c1earest results have been obtained from Mediterranean populations of
Siganus rivulatus and S.luridus. The two fishes have carried into the Mediterranean some of their Red Sea monogeneans : Pseudohalitrematoides oramini
The Migrant Biota
explain, for instance, why Cassiopea andromeda, the medusa which was so successful in colonizing the Canal, did not succeed in expanding into the Mediterranean.
The broad ecological valency of the Lessepsian migrants makes them very
successful in the intraspecific competition in their new environment. Therefore,
the biotic relationships established in the Mediterranean between the invaders
and the autochthones probably-within certain environmental limits-lead to
the success ofthe Lessepsian migrants.
Unlike some ofthe well-known invasional episodes ofterrestrial zoology, the
Lessepsian migration is a success story. The Lessepsian migrants are gradually
building up their populations and expanding within their new marine province. I
know of no case in which a Lessepsian migrant recorded at an early date disappeared afterwards. There are no reported cases of area restriction following the
primary expansion. There were no population explosions and population crashes.
Unfortunately, the process of colonization, of niche conquest, or of species
displacement has not been followed and studied even in one single Lessepsian
species. The few scattered and circumstantial data available in order to describe
the fate ofthe Lessepsian migrants within their new environments are compiled in
Chapter 3.7.
A highly significant subject for investigation reiated to Lessepsian migration
has only recently been approached: the study of the parasite fauna of the migrants
can be of importance in three very important respects: (1) comparative parasitology may give additional c1ues, confrrm or disprove zoogeographical conc1usions;
(2) it may explain the success of the migrant in its new environment; and (3) it
may indicate newly established interactions between local and newcomer species
and reveal a potential threat of epidemics.
Unfortunately, the only data available are those concerning ichthyoparasites,
and these data are provided exc1usively by the work done by Paperna and some of
his collaborators. In Paperna's words (1972d): "Parasites may be introduced by
migrant fish and consequently infect the autochthonous fish. The change in the
environment may increase the pathogenic effect of the parasites on their original
migrant host. The original parasitofauna of the migrant host may be lost altogether in the new environment."
Paperna (1972d) conc1udes that endoparasites cannot migrate unless their
intermediary hosts, i.e. invertebrate species, actually migrate together with the fish
species. Only the snail Pirenella cailliaudi which is known to harbor metacercariae of several species of helminths, might be a source for endoparasites alien to
the Mediterranean.
Ectoparasites migrate together with their hosts if they are euryhaline and
eurythermal enough. A "c1eaning" of the fish through migration into a more
saline environment has been documented by Paperna and Lahav (1975) for the
Mugil species ofthe Sirbonic lagoon (Bardawil).
The ectoparasitic monogenean Ancyrocephalus salinus has followed its host
Aphanius dispar everywhere: it is known from the Red Sea, the Mediterranean,
and also from the landlocked springs arol!lld the Dead Sea (paperna, 1964).
The c1earest results have been obtained from Mediterranean populations of
Siganus rivulatus and S.luridus. The two fishes have carried into the Mediterranean some of their Red Sea monogeneans : Pseudohalitrematoides oramini