The Levant Basin of the Mediterranean
121
implications for the animal and vegetal populations are obvious: a elearcut quantitative and qualitative impoverishment with indications of smaller individual
sizes.
I could not [md comparative data for the planktonie biomasses. Such data are
available however for the benthic level-bottom biomasses and they elearly illustrate the poverty of the Levant Basin. Tchukhtchin (1964) found an average
benthic biomass of 0.089 gjm 2 in the Eastern Mediterranean between 2001000 m. For depths less than 200 m he indicates a value of 4.12 gjm 2 on the SieilyTunisia sill, as compared to values of 266.4 gjm 2 in the Atlantie, or even 388 gjm 2
in the Black Sea. Gilat (1964) compares the benthie biomass of the circalittoral
shelf areas and gives values of 8-16 gjm 2 for the Eastern Mediterranean and 48126 gjm 2 for the Adriatic. Surprisingly low values are indicated by Tchukhtchin
(1964) for Mersin Bay in the northeastern corner of the Levant: 0.008 gjm 2 at
173 m. This is probably a rather extreme case of faunal scarcity, lower than the
usuallow of the area, and probably based only on macrobenthic biomass. Gilat's
(1964) macrobenthos biomass values from the shelf of Israel are in the extremely
low range of 0.059 to 0.075 gjm 2 • There is only one notable exception in the
Levant Basin-or rather at its southwestern limits-the fishery grounds off Alexandria, where Vatova (1935) found 551 gjm 2 ; Kiseleva and Tchukhtchin (1965)
reported 500 gjm 2 for astation near Alexandria. Such high biomasses were probably found all along the shores of the Nile Delta and speak for the local influence
ofthe nutrient rieh fluviatile deposits ofthe Nile. For the Levant Basin as a whole,
the nutrient enrichment by the Nile water had always had only a strictly localized
and seasonal character.
The impoverishment towards the east is especially well-documented in the
qualitative aspect. The species diversity of all the environments is sharply decreasing in something like two steps: the Western Mediterranean-+Aegaean Sea-+the
Levant Basin. There are 118 Atlantie species of the planktonie Hyperiidea (Amphipoda) and 46 species in the Western Mediterranean. In the Eastern basin there are
only about 10 species. Eight species of Pteropoda of the Western Mediterranean
do not reach the Eastern part. Alvarifio (1974), reviewing the Siphonophora,
writes: "Many species do not reach the Levant Mediterranean basin, and only
appear accidentally there, a few get settled in the area". Recently Godeaux (1974)
documented the same paucity with respect to the Thaliacea (salps), mentioning in
particular the lack ofthe genus Pyrosoma in the Levant Basin.
For the benthic organisms the impoverishment is much better documented.
There are whole categories of habitat-forming organisms whieh are missing, such
as the water plant Posidonia oceanica and the wealth of the Western Mediterranean gorgonarians. No single species of Gorgonacea has reached the Levant
coast. The impoverishment is equally impressive among the Decapoda and the
Echinodermata. Peres (1958a) analyzes the populations of Ascidiacea along the
Israel coast and remarks that the families Moigulidae and Polyelinidae are very
scarce or absent. He mentions eight species of Moigulidae in the Western Mediterranean, four species in the Sicily-Tunisia area, ~me species in the Aegean Sea
and none along the Israel coast. The Polyelinidae, which still form 15-20% of the
Ascidian diversity in the Aegean Sea, are represented among the 33 species of the
Israel coast by only one species, Amarocium lobatum.
121
implications for the animal and vegetal populations are obvious: a elearcut quantitative and qualitative impoverishment with indications of smaller individual
sizes.
I could not [md comparative data for the planktonie biomasses. Such data are
available however for the benthic level-bottom biomasses and they elearly illustrate the poverty of the Levant Basin. Tchukhtchin (1964) found an average
benthic biomass of 0.089 gjm 2 in the Eastern Mediterranean between 2001000 m. For depths less than 200 m he indicates a value of 4.12 gjm 2 on the SieilyTunisia sill, as compared to values of 266.4 gjm 2 in the Atlantie, or even 388 gjm 2
in the Black Sea. Gilat (1964) compares the benthie biomass of the circalittoral
shelf areas and gives values of 8-16 gjm 2 for the Eastern Mediterranean and 48126 gjm 2 for the Adriatic. Surprisingly low values are indicated by Tchukhtchin
(1964) for Mersin Bay in the northeastern corner of the Levant: 0.008 gjm 2 at
173 m. This is probably a rather extreme case of faunal scarcity, lower than the
usuallow of the area, and probably based only on macrobenthic biomass. Gilat's
(1964) macrobenthos biomass values from the shelf of Israel are in the extremely
low range of 0.059 to 0.075 gjm 2 • There is only one notable exception in the
Levant Basin-or rather at its southwestern limits-the fishery grounds off Alexandria, where Vatova (1935) found 551 gjm 2 ; Kiseleva and Tchukhtchin (1965)
reported 500 gjm 2 for astation near Alexandria. Such high biomasses were probably found all along the shores of the Nile Delta and speak for the local influence
ofthe nutrient rieh fluviatile deposits ofthe Nile. For the Levant Basin as a whole,
the nutrient enrichment by the Nile water had always had only a strictly localized
and seasonal character.
The impoverishment towards the east is especially well-documented in the
qualitative aspect. The species diversity of all the environments is sharply decreasing in something like two steps: the Western Mediterranean-+Aegaean Sea-+the
Levant Basin. There are 118 Atlantie species of the planktonie Hyperiidea (Amphipoda) and 46 species in the Western Mediterranean. In the Eastern basin there are
only about 10 species. Eight species of Pteropoda of the Western Mediterranean
do not reach the Eastern part. Alvarifio (1974), reviewing the Siphonophora,
writes: "Many species do not reach the Levant Mediterranean basin, and only
appear accidentally there, a few get settled in the area". Recently Godeaux (1974)
documented the same paucity with respect to the Thaliacea (salps), mentioning in
particular the lack ofthe genus Pyrosoma in the Levant Basin.
For the benthic organisms the impoverishment is much better documented.
There are whole categories of habitat-forming organisms whieh are missing, such
as the water plant Posidonia oceanica and the wealth of the Western Mediterranean gorgonarians. No single species of Gorgonacea has reached the Levant
coast. The impoverishment is equally impressive among the Decapoda and the
Echinodermata. Peres (1958a) analyzes the populations of Ascidiacea along the
Israel coast and remarks that the families Moigulidae and Polyelinidae are very
scarce or absent. He mentions eight species of Moigulidae in the Western Mediterranean, four species in the Sicily-Tunisia area, ~me species in the Aegean Sea
and none along the Israel coast. The Polyelinidae, which still form 15-20% of the
Ascidian diversity in the Aegean Sea, are represented among the 33 species of the
Israel coast by only one species, Amarocium lobatum.