Plankton Relations of the Red Sea, Persian Gulf and Arabian Sea
227
discussion fit into the pattern outlined above, the information regarding the phytoplankton of the Red Sea is clearly inferior to that for the Arabian Sea.
Most of the data are of a qualitative nature and generally relate to a given season
rather than to a complete year cycle. Nevertheless, some of the basic features of the
phytoplankton of these regions include such features as a dominance of dinoflagellates
as compared with diatoms in the Red Sea, the almost complete absence of diatom blooms
in the Red Sea, and the non-occurrence of certain species in the various areas of this sea
while preserving floristic affiliations with the Indian Ocean as a whole.
Regarding the Persian Gulf and the Gulf of Oman, BOHM (1931) stresses the poverty
in species of dinoflagellates in this region as compared with the Arabian Sea. It is interesting to note that among the 38 species of dinoflagellates reported by this author are
Ceratium carriense and C. trichoceros, 2 of the 4 species considered by SUKHANOVA
(1962) as constituting the "basic Indo-oceanic complex".
IV. Zooplankton
The groups considered in this section will of necessity be those which have received
most attention throughout the years, mainly due to their major role in the total plankton
biomass. Among such groups the copepods and the euphausiids are probably the most
important. The earlier work on the copepods of the Red Sea is summed up by HALIM
(1969). He notes that, out of a total of 270 species of calanoid copepods known from
the Indian Ocean, 158 species are recorded from the Red Sea, this being the list compiled
by him from all existing sources to date - primarily SEWELL's records (1948) from his
study of the free-living planktonic copepods of this region. In his view, the restricted
copepod fauna of the Red Sea, a large proportion of which is of a deep-water type, is
due to the physical barrier of the sill at Bab-el-Mandeb which prevents the influx of
Indo-Pacific species. This decreasing trend in the number of species continues northward
and there is evidence that still fewer species among those which succeed in settling in
the southern Red Sea actually reach the northern Gulfs of Suez and Eilat.
The seasonal aspect is also of importance in the consideration of this group. According
to HALIM (1969), the copepods are represented by the largest numbers of species in
winter, which is clearly a result of the inflow of surface waters from the Gulf of Aden
during the NE monsoon. The subsequent decrease in the number of copepod species
during the summer as noted by HALIM may well be caused by the well-known phenomenon
observed by many investigators including the author whereby winter epipelagic species
sink to deeper levels during the hot summer months.
Recently BERDUGO (in preparation) made a preliminary study of the calanoid copepods
of the Gulf of Eilat noting the considerably poorer fauna of this region as compared
with that of the southern Red Sea and to an even greater degree with that of the Arabian
Sea.
The question of endemic species is, however, a complex one. While recognizing the
existence of such species which seem to have had their origin in the Red Sea such as
Acartia fossae, Candacia samassae and Labidocera orsini, among others, Candacia
samassae has since been recorded by JONES (1966 a) in the Arabian Sea and the Bay of
Bengal. It is thus suggested that there should not be hard and fast rules in the drawing
up of zoogeographical boundaries as they may be subject to changes as a result of more
227
discussion fit into the pattern outlined above, the information regarding the phytoplankton of the Red Sea is clearly inferior to that for the Arabian Sea.
Most of the data are of a qualitative nature and generally relate to a given season
rather than to a complete year cycle. Nevertheless, some of the basic features of the
phytoplankton of these regions include such features as a dominance of dinoflagellates
as compared with diatoms in the Red Sea, the almost complete absence of diatom blooms
in the Red Sea, and the non-occurrence of certain species in the various areas of this sea
while preserving floristic affiliations with the Indian Ocean as a whole.
Regarding the Persian Gulf and the Gulf of Oman, BOHM (1931) stresses the poverty
in species of dinoflagellates in this region as compared with the Arabian Sea. It is interesting to note that among the 38 species of dinoflagellates reported by this author are
Ceratium carriense and C. trichoceros, 2 of the 4 species considered by SUKHANOVA
(1962) as constituting the "basic Indo-oceanic complex".
IV. Zooplankton
The groups considered in this section will of necessity be those which have received
most attention throughout the years, mainly due to their major role in the total plankton
biomass. Among such groups the copepods and the euphausiids are probably the most
important. The earlier work on the copepods of the Red Sea is summed up by HALIM
(1969). He notes that, out of a total of 270 species of calanoid copepods known from
the Indian Ocean, 158 species are recorded from the Red Sea, this being the list compiled
by him from all existing sources to date - primarily SEWELL's records (1948) from his
study of the free-living planktonic copepods of this region. In his view, the restricted
copepod fauna of the Red Sea, a large proportion of which is of a deep-water type, is
due to the physical barrier of the sill at Bab-el-Mandeb which prevents the influx of
Indo-Pacific species. This decreasing trend in the number of species continues northward
and there is evidence that still fewer species among those which succeed in settling in
the southern Red Sea actually reach the northern Gulfs of Suez and Eilat.
The seasonal aspect is also of importance in the consideration of this group. According
to HALIM (1969), the copepods are represented by the largest numbers of species in
winter, which is clearly a result of the inflow of surface waters from the Gulf of Aden
during the NE monsoon. The subsequent decrease in the number of copepod species
during the summer as noted by HALIM may well be caused by the well-known phenomenon
observed by many investigators including the author whereby winter epipelagic species
sink to deeper levels during the hot summer months.
Recently BERDUGO (in preparation) made a preliminary study of the calanoid copepods
of the Gulf of Eilat noting the considerably poorer fauna of this region as compared
with that of the southern Red Sea and to an even greater degree with that of the Arabian
Sea.
The question of endemic species is, however, a complex one. While recognizing the
existence of such species which seem to have had their origin in the Red Sea such as
Acartia fossae, Candacia samassae and Labidocera orsini, among others, Candacia
samassae has since been recorded by JONES (1966 a) in the Arabian Sea and the Bay of
Bengal. It is thus suggested that there should not be hard and fast rules in the drawing
up of zoogeographical boundaries as they may be subject to changes as a result of more