470
A. A. NEYMAN, M. N. SOKOLOVA, N. G. VINOGRADOVA, and F. A. PASTERNAK:
entirely absent. It is only below the H2S layer that the biomass of bottom invertebrates
begins to increase again (0.22- 0.44 g m- 2 ).
It is possible that the existence in the eastern part of the Arabian Sea of a constant
circulation with water sinking at its centre, may lead to the creation of a halistatic area,
where an impoverishment in food resources down to the bottom may easily be assumed.
At any rate the benthos biomass in this region is reduced to 0.3 g m- 2 •
At the same time the general productivity of the bottom population of the Arabian Sea
is still very high, and its wealth presents a phenomenon which is quite extraordinary for
the tropical zone. Judging from several bottom samples taken with grabs, high indices of
biomass are characteristic also of the great depths near the NW coasts of Africa (up to
1 g m- 2 ). This is the area worked by the German expedition on the "Meteor" which,
among other research work, carried out investigations on the quantitative distribution of
meiofauna. The data obtained show a high density of the colonies of these bottom
organisms (up to 170 000 indo m -2). Unfortunately, no quantitative determinations were
made of the biomass of meiofauna (THIEL, 1966). The abundance of life in the whole
water column of the region under consideration may be explained by an intensive ascent of
deep waters, brought about by the monsoon current spreading out northwards and
southwards like a broad fan.
The quantitative distribution of benthos presents quite another picture in the Bay
of Bengal, the floor of which is an accumulative plain with little relief. Owing to the
lowered salinity of the surface layer, the sharp stratification of water within the Bay,
and the sinking of the layer of density discontinuity to a depth of 100 m, the phytoplankton is extremely poor, as is the zooplankton. These factors are also responsible for
the feeble development of bottom life in the Bay of Bengal. The benthos biomass in the
open part of the Bay is very evenly distributed and varies between 0.11 and 0.45 g m -2.
At one of the stations in its central part the bottom fauna was found to be as low as
0.06 g m- 2 , and still lower (0.04 g m- 2 ) in the western part. Analogous values of benthos
biomass are characteristic of the central regions of the Andaman Sea (SOKOLOVA and
PASTERNAK, 1962, 1964).
A very low benthos biomass (less than 0.2 g m- 2 ) was recorded in the open deepwater part of the Indian Ocean situated within the tropical zone.
In the more productive western half of the ocean the bottom fauna is more abundant
than in its eastern half. Here, as a rule the biomass of benthos is never less than 0.1 g m- 2
(a lower biomass was recorded only in the SW part of the Mascarene Basin and in an
area lying to the north of the Equator between longitudes 55° and 70° E). The benthos
of the eastern half of the Ocean is extremely poor. Here an area of minimum development
of bottom life between latitudes 5° and 30° S closely coincides with a subtropical circulation of waters of extremely low productivity. The biomass of benthos in this area does
not exceed 0.05 g m -2, with an average of 0.04 g m -2.
Southwards, beyond the tropical zone, the biomass of bottom fauna increases again
reaching no less than 0.2 - 0.4 g m -2 to the south of latitude 30 ° S.
Most important in the biomass of bottom fauna are polychaetes, especially at great
depths (50%); in shallow-water areas crustaceans are almost as important as polychaetes
(25%), with a predominance of decapods and amphipods (21 %), followed by the epifauna
(15%). At great depths the proportion of crustaceans is reduced to 10% with a predominance of Tanaidacea and Isopoda. Sponges become more important, while molluscs
play an insignificant part at all depths.
A. A. NEYMAN, M. N. SOKOLOVA, N. G. VINOGRADOVA, and F. A. PASTERNAK:
entirely absent. It is only below the H2S layer that the biomass of bottom invertebrates
begins to increase again (0.22- 0.44 g m- 2 ).
It is possible that the existence in the eastern part of the Arabian Sea of a constant
circulation with water sinking at its centre, may lead to the creation of a halistatic area,
where an impoverishment in food resources down to the bottom may easily be assumed.
At any rate the benthos biomass in this region is reduced to 0.3 g m- 2 •
At the same time the general productivity of the bottom population of the Arabian Sea
is still very high, and its wealth presents a phenomenon which is quite extraordinary for
the tropical zone. Judging from several bottom samples taken with grabs, high indices of
biomass are characteristic also of the great depths near the NW coasts of Africa (up to
1 g m- 2 ). This is the area worked by the German expedition on the "Meteor" which,
among other research work, carried out investigations on the quantitative distribution of
meiofauna. The data obtained show a high density of the colonies of these bottom
organisms (up to 170 000 indo m -2). Unfortunately, no quantitative determinations were
made of the biomass of meiofauna (THIEL, 1966). The abundance of life in the whole
water column of the region under consideration may be explained by an intensive ascent of
deep waters, brought about by the monsoon current spreading out northwards and
southwards like a broad fan.
The quantitative distribution of benthos presents quite another picture in the Bay
of Bengal, the floor of which is an accumulative plain with little relief. Owing to the
lowered salinity of the surface layer, the sharp stratification of water within the Bay,
and the sinking of the layer of density discontinuity to a depth of 100 m, the phytoplankton is extremely poor, as is the zooplankton. These factors are also responsible for
the feeble development of bottom life in the Bay of Bengal. The benthos biomass in the
open part of the Bay is very evenly distributed and varies between 0.11 and 0.45 g m -2.
At one of the stations in its central part the bottom fauna was found to be as low as
0.06 g m- 2 , and still lower (0.04 g m- 2 ) in the western part. Analogous values of benthos
biomass are characteristic of the central regions of the Andaman Sea (SOKOLOVA and
PASTERNAK, 1962, 1964).
A very low benthos biomass (less than 0.2 g m- 2 ) was recorded in the open deepwater part of the Indian Ocean situated within the tropical zone.
In the more productive western half of the ocean the bottom fauna is more abundant
than in its eastern half. Here, as a rule the biomass of benthos is never less than 0.1 g m- 2
(a lower biomass was recorded only in the SW part of the Mascarene Basin and in an
area lying to the north of the Equator between longitudes 55° and 70° E). The benthos
of the eastern half of the Ocean is extremely poor. Here an area of minimum development
of bottom life between latitudes 5° and 30° S closely coincides with a subtropical circulation of waters of extremely low productivity. The biomass of benthos in this area does
not exceed 0.05 g m -2, with an average of 0.04 g m -2.
Southwards, beyond the tropical zone, the biomass of bottom fauna increases again
reaching no less than 0.2 - 0.4 g m -2 to the south of latitude 30 ° S.
Most important in the biomass of bottom fauna are polychaetes, especially at great
depths (50%); in shallow-water areas crustaceans are almost as important as polychaetes
(25%), with a predominance of decapods and amphipods (21 %), followed by the epifauna
(15%). At great depths the proportion of crustaceans is reduced to 10% with a predominance of Tanaidacea and Isopoda. Sponges become more important, while molluscs
play an insignificant part at all depths.