228
B. KIMOR:
intensive sampling in time and space. At the same time the same author (JONES, 1966 b)
notes that geographically remote populations of the same species may have distinct
morphological features such as he noted with regard to Candacia pachydactyla from the
Atlantic and the Indo-Pacific oceans.
The euphausiids of the Indian Ocean have also formed the subject of significant
contributions in recent years. The important role of members of this group in the total
planktonic biomass of the Arabian Sea and the Bay of Bengal, emphasized by PONOMAREVA (1964), is contrary to the habits of this group in other tropical areas. In a consideration of the euphausiids of the Red Sea, the same author (PONOMAREVA, 1968) discusses
the importance of this group for fisheries. Out of 22 species known from the Indian Ocean
10 are known from the Red Sea, most of them being immigrants from the Gulf of Aden.
Most of these species are surface forms which could easily pass the Strait of Bab-elMandeb. A few endemic species are known from the Red Sea such as Euphausia sanzoi
and Pseudoeuphausia colosi. A more recent work on this group by WEIGMANN (1970)
deals with the euphausiids of the Arabian Sea during the NE monsoon. The author
defined 5 distinct areas, namely, the Arabian Sea proper with 24 species, the Gulf of
Aden with 10 species, the Red Sea with 6 species, the Gulf of Oman with 5 species and
the Persian Gulf with 1 species. However, some of the highest concentrations per unit
volume of 100 m 3 were recorded in the Persian Gulf and consist of the single species
Pseudoeuphasia latifrons. Similar patches were also recorded in some parts of the Malabar
coast of SW India and in some parts of the Gulf of Aden. These areas of high production
are zones of upwelling during the NE monsoon; in the Central Arabian Sea lower
concentrations were recorded. (Fig. 6).
According to WEIGMANN, the similarity between the euphausiid fauna of the Red
Sea and the Gulf of Aden is due to the fact that during the NE monsoon deep water from
the Red Sea flows southward into the Gulf of Aden while the surface current flows into
the Red Sea.
The distribution of euphausiids in the Indian Ocean as a whole and the increase in
numbers of euphausiids on the western side of the Indian Ocean is emphasized by
GOPALAKRISHNAN and BRINTON (1969) who also stress the importance of this group
as food for fishes of commercial importance.
WICKSTEAD (1963) mentions 3 species of Cladocera from the Zanzibar area on the
East African coast, namely Evadne tergestina, Podon polyphemoides and Penilia
avirostris. These are well-known species, common in all tropical and subtropical regions,
including the Mediterranean. WICKSTEAD correlates the sporadic swarming of Penilia
avirostris with an ample supply of O2 in the water which may be caused by occasional
diatom blooms. In our regular collections in the Gulf of Eilat, the only species so far
recorded and perennial in its distribution is Evadne tergestina (KOMAROVSKY, 1958).
The presence of Penilia avirostris was recently reported from the Gulf of Suez during
February 1971 (POR, personal information).
GEORGE (1969) discusses the distribution of planktonic ostracods in the Indian Ocean
and notes the exceptionally high numbers of some of the species in the northern part of
the Arabian Sea, especially in coastal waters. No recent data are, however, available for
the Red Sea area although earlier information is reported by HALIM (1969) emphasizing
the Indo-Pacific character of the prevailing species.
Further evidence on the selective distribution of species in adjoining seas is provided
by FRONTIER (1963 b) reporting on the pteropods of the Arabian Sea, Persian Gulf and
B. KIMOR:
intensive sampling in time and space. At the same time the same author (JONES, 1966 b)
notes that geographically remote populations of the same species may have distinct
morphological features such as he noted with regard to Candacia pachydactyla from the
Atlantic and the Indo-Pacific oceans.
The euphausiids of the Indian Ocean have also formed the subject of significant
contributions in recent years. The important role of members of this group in the total
planktonic biomass of the Arabian Sea and the Bay of Bengal, emphasized by PONOMAREVA (1964), is contrary to the habits of this group in other tropical areas. In a consideration of the euphausiids of the Red Sea, the same author (PONOMAREVA, 1968) discusses
the importance of this group for fisheries. Out of 22 species known from the Indian Ocean
10 are known from the Red Sea, most of them being immigrants from the Gulf of Aden.
Most of these species are surface forms which could easily pass the Strait of Bab-elMandeb. A few endemic species are known from the Red Sea such as Euphausia sanzoi
and Pseudoeuphausia colosi. A more recent work on this group by WEIGMANN (1970)
deals with the euphausiids of the Arabian Sea during the NE monsoon. The author
defined 5 distinct areas, namely, the Arabian Sea proper with 24 species, the Gulf of
Aden with 10 species, the Red Sea with 6 species, the Gulf of Oman with 5 species and
the Persian Gulf with 1 species. However, some of the highest concentrations per unit
volume of 100 m 3 were recorded in the Persian Gulf and consist of the single species
Pseudoeuphasia latifrons. Similar patches were also recorded in some parts of the Malabar
coast of SW India and in some parts of the Gulf of Aden. These areas of high production
are zones of upwelling during the NE monsoon; in the Central Arabian Sea lower
concentrations were recorded. (Fig. 6).
According to WEIGMANN, the similarity between the euphausiid fauna of the Red
Sea and the Gulf of Aden is due to the fact that during the NE monsoon deep water from
the Red Sea flows southward into the Gulf of Aden while the surface current flows into
the Red Sea.
The distribution of euphausiids in the Indian Ocean as a whole and the increase in
numbers of euphausiids on the western side of the Indian Ocean is emphasized by
GOPALAKRISHNAN and BRINTON (1969) who also stress the importance of this group
as food for fishes of commercial importance.
WICKSTEAD (1963) mentions 3 species of Cladocera from the Zanzibar area on the
East African coast, namely Evadne tergestina, Podon polyphemoides and Penilia
avirostris. These are well-known species, common in all tropical and subtropical regions,
including the Mediterranean. WICKSTEAD correlates the sporadic swarming of Penilia
avirostris with an ample supply of O2 in the water which may be caused by occasional
diatom blooms. In our regular collections in the Gulf of Eilat, the only species so far
recorded and perennial in its distribution is Evadne tergestina (KOMAROVSKY, 1958).
The presence of Penilia avirostris was recently reported from the Gulf of Suez during
February 1971 (POR, personal information).
GEORGE (1969) discusses the distribution of planktonic ostracods in the Indian Ocean
and notes the exceptionally high numbers of some of the species in the northern part of
the Arabian Sea, especially in coastal waters. No recent data are, however, available for
the Red Sea area although earlier information is reported by HALIM (1969) emphasizing
the Indo-Pacific character of the prevailing species.
Further evidence on the selective distribution of species in adjoining seas is provided
by FRONTIER (1963 b) reporting on the pteropods of the Arabian Sea, Persian Gulf and