Analysis of the Colonizing Success of Lessepsian Migrants
147
Turning now to the littoral rock dwellers, information becomes increasingly
scarce. Safriel and Lipkin (1975) compared the repartition of222 species along the
Intertidal zonation pattern ofthe Mediterranean coast at Mikhmoret-201 native
species and 21 Lessepsian species. They found no immigrants in the Supralittoral,
fewer in the Upper Midlittoral than proportionally expected, normal proportions
in the Mid Midlittoral and Lower Midlittoral and a relatively higher proportion
than expected in the Infralittoral. Several of Safriel's students are at present
studying the interspecific relationship between native and colonizing species in
the rocky littoral : Felsenburg (1974) could not find any clearcut difference between the present vertical distribution of the autochthonous M ytilus minimus and
the migrant Brachidontes variabilis. These two species appear interspersed, and B.
variabilis did not change its vertical distribution in the intertidal belt after entering the Mediterranean. Ayal (unpublished) is studying the competition assumed
to exist between the colonizing species Cerithium scabridum and the non-colonizing autochthonous Cerithium rupestre. The two species occur together along the
shores of Israel, north of Caesarea. Ayal has found C. scabridum to be dominant at
present, sometimes with thousands of specimens per square meter, in a site in the
Bay of 'Akko (Acre) where in 1964, according to Safriel, C. rupestre was dominant. According to Ayal there is an explosive settling of young specimens of C.
scabridum in September-October but during the winter the cold frequently destroys the whole population of settlers. It is important to mention that Cerithium
scabridum lives in the shallowest tens of centimeters of water where the cooling in
the winter is most drastically feIt.
The Bay of Acre is an especially favorable site for the Red Sea immigrants.
The bay is sheltered from the open sea by the additional structures of the old
Crusader and Turkish port; pollution is minimal since the harbor is used only by
small fishing craft. The waters are quiet, undisturbed and warm. This environment shows at present the most abundant populations of the pearl oyster Pinctada radiata on the Israel coasts: the pearl oyster forms wh oIe reef-like structures.
It is here that huge concentrations of the red-colored immigrant crab Atergatis
roseus are found, a species first reported in the Mediterranean in 1961.
The little sea star Asterina wega is very frequent at 'Akko (Acre). Achituv
(1969, 1973) has studied the appearance of this Lessepsian migrant in the Mediterranean and the parallel disappearance of the autochthonous Asterina gibbosa.
A. wega was first collected in small numbers in Haifa Bay, in 1955. Since then it
underwent a regular population explosion and is found by the thousands. Achituv
(1973) collected 530 specimens of tbis little sea star at Akhziv on one single
occasion in June 1970.
It seems that in some relation with the appearance of A. wega, the other
species A. gibbosa disappeared. Out of the 37 specimens of A. gibbosa found by
Achituv in the collections of the Hebrew University, 34 were sampled at 'Atlit
between 1934 and 1944. In 1970 Achituv was unable to find any A. gibbosa on the
collecting sites of 'Atlit whence most of the known specimens came. The locality,
however, yielded specimens of A. wega. It seems tliat A. gibbosa was last collected
at Shiqmona in 1963. On the island of Cyprus, according to Achituv, A. gibbosa
alone is found, and frequently.
147
Turning now to the littoral rock dwellers, information becomes increasingly
scarce. Safriel and Lipkin (1975) compared the repartition of222 species along the
Intertidal zonation pattern ofthe Mediterranean coast at Mikhmoret-201 native
species and 21 Lessepsian species. They found no immigrants in the Supralittoral,
fewer in the Upper Midlittoral than proportionally expected, normal proportions
in the Mid Midlittoral and Lower Midlittoral and a relatively higher proportion
than expected in the Infralittoral. Several of Safriel's students are at present
studying the interspecific relationship between native and colonizing species in
the rocky littoral : Felsenburg (1974) could not find any clearcut difference between the present vertical distribution of the autochthonous M ytilus minimus and
the migrant Brachidontes variabilis. These two species appear interspersed, and B.
variabilis did not change its vertical distribution in the intertidal belt after entering the Mediterranean. Ayal (unpublished) is studying the competition assumed
to exist between the colonizing species Cerithium scabridum and the non-colonizing autochthonous Cerithium rupestre. The two species occur together along the
shores of Israel, north of Caesarea. Ayal has found C. scabridum to be dominant at
present, sometimes with thousands of specimens per square meter, in a site in the
Bay of 'Akko (Acre) where in 1964, according to Safriel, C. rupestre was dominant. According to Ayal there is an explosive settling of young specimens of C.
scabridum in September-October but during the winter the cold frequently destroys the whole population of settlers. It is important to mention that Cerithium
scabridum lives in the shallowest tens of centimeters of water where the cooling in
the winter is most drastically feIt.
The Bay of Acre is an especially favorable site for the Red Sea immigrants.
The bay is sheltered from the open sea by the additional structures of the old
Crusader and Turkish port; pollution is minimal since the harbor is used only by
small fishing craft. The waters are quiet, undisturbed and warm. This environment shows at present the most abundant populations of the pearl oyster Pinctada radiata on the Israel coasts: the pearl oyster forms wh oIe reef-like structures.
It is here that huge concentrations of the red-colored immigrant crab Atergatis
roseus are found, a species first reported in the Mediterranean in 1961.
The little sea star Asterina wega is very frequent at 'Akko (Acre). Achituv
(1969, 1973) has studied the appearance of this Lessepsian migrant in the Mediterranean and the parallel disappearance of the autochthonous Asterina gibbosa.
A. wega was first collected in small numbers in Haifa Bay, in 1955. Since then it
underwent a regular population explosion and is found by the thousands. Achituv
(1973) collected 530 specimens of tbis little sea star at Akhziv on one single
occasion in June 1970.
It seems that in some relation with the appearance of A. wega, the other
species A. gibbosa disappeared. Out of the 37 specimens of A. gibbosa found by
Achituv in the collections of the Hebrew University, 34 were sampled at 'Atlit
between 1934 and 1944. In 1970 Achituv was unable to find any A. gibbosa on the
collecting sites of 'Atlit whence most of the known specimens came. The locality,
however, yielded specimens of A. wega. It seems tliat A. gibbosa was last collected
at Shiqmona in 1963. On the island of Cyprus, according to Achituv, A. gibbosa
alone is found, and frequently.