472
A. A. NEYMAN, M. N. SOKOLOVA, N. G. VINOGRADOVA, and F. A. PASTERNAK:
A distinct zonality is observed in their distribution, determined by the relief of the sea
floor and the type of sedimentation. In the immediate proximity of the shore, in the
region of transit of suspended matter, seston-feeding epifauna invertebrates usually
predominate. Further out, with the gradual decrease of water movement and increasing
precipitation of suspended matter, seston-feeders give way to detritophages sorting out
detritus from the surface of the sediments, and then to detritophages swallowing detritus
together with the mud.
As in all other oceans, eutrophic conditions may arise along all the periphery of the
Indian Ocean even at depths below 3000 m (Fig. 2). Consequently, the eutrophic region
encompasses the Arabian Sea with the adjacent Somali Basin, the Mascarene and Mozambique Basins, the Bay of Bengal with the adjacent parts of the Central Indian and Coco
Basins, the deep-sea Java Trench, the greater of the rift zone, the southern part of the
Crozet Basin and, finally, both the Antarctic Basins. The sediments of the vast eutrophic
area of the Indian Ocean are represented by foraminiferan and radiolarian oozes in the
north, and diatom oozes in the south. The content of organic C in the sediments varies in
different parts of the region but is generally no less than 0.3 % (by weight), Eh is characterized by negative or low positive values, and the oxygenated layer is either absent or of insignificant thickness (BEZRUKOV, 1964; LISITZIN, 1960). Both seston-feeding and detritusfeeding invertebrates are widely distributed in the macrobenthos of the eutrophic region.
As in shallow-water areas, their spatial distribution is determined by the food supply,
bottom relief and local rate of sedimentation. A detailed study of the distribution of
trophic groups was carried out in particular in the Bay of Bengal (SOKOLOVA and PASTERNAK, 1964), and it was possible to demonstrate a clear-cut succession of zones of predominant development of a certain type of feeding, with increasing depth and under the
effect of changing macrorelief and feeding conditions. A predominance of seston-feeders
in the lower part of the shelf is succeeded by a predominance of sorting detritophages on
the slope and indiscriminate detritophages in the depths of the central part of the bay.
Unlike the Pacific and the Atlantic Oceans, the Indian Ocean, owing to its position
in the tropical belt and in the southern temperate zone, has only one oligotrophic area.
This region occupies the southern parts of the Central Indian Basin, the Australian
Basin and the northern half of the Crozet Basin and coincides with the boundaries of a
southern subtropical gyre characterized by waters of extremely low productivity. This
part of the ocean is more than 3 800 - 4 000 m deep. The sediments in the northern
part of the oligotrophic region (down to latitudes 15 _17 0 S) are represented by radioliterally paved with them. The content of organic C in the sediments of the oligotrophic
oozes. Ferro manganese concretions are widespread here and in places the sea floor is
larian oozes and in the southern part by deep-sea red clays and carbonate-foraminiferan
area is 0.3 % or less, while En reaches high positive values. In the sediments of the northern
half of the region, minimum concentrations of humic acids were recorded, a fact which
is directly related to the low content of organic C (BORDOVSKY, 1964).
The macrobenthos of the oligotrophic region is characterized by a general quantitative
and qualitative impoverishment of bottom fauna; prevalent here are sestonophagous
invertebrates which feed on particulate matter from the bottom water layer, e.g. sponges,
cirripedes and polychaetes of the Serpulidae family. Detritus feeders which swallow
detritus together with the mud, such as holothurians, irregular sea-urchins or sea-stars
are entirely absent. In the trawl catches, the ratio by weight of seston-feeding to detritusfeeding invertebrates is expressed in values lower than unity, irrespective of the mesorelief.
A. A. NEYMAN, M. N. SOKOLOVA, N. G. VINOGRADOVA, and F. A. PASTERNAK:
A distinct zonality is observed in their distribution, determined by the relief of the sea
floor and the type of sedimentation. In the immediate proximity of the shore, in the
region of transit of suspended matter, seston-feeding epifauna invertebrates usually
predominate. Further out, with the gradual decrease of water movement and increasing
precipitation of suspended matter, seston-feeders give way to detritophages sorting out
detritus from the surface of the sediments, and then to detritophages swallowing detritus
together with the mud.
As in all other oceans, eutrophic conditions may arise along all the periphery of the
Indian Ocean even at depths below 3000 m (Fig. 2). Consequently, the eutrophic region
encompasses the Arabian Sea with the adjacent Somali Basin, the Mascarene and Mozambique Basins, the Bay of Bengal with the adjacent parts of the Central Indian and Coco
Basins, the deep-sea Java Trench, the greater of the rift zone, the southern part of the
Crozet Basin and, finally, both the Antarctic Basins. The sediments of the vast eutrophic
area of the Indian Ocean are represented by foraminiferan and radiolarian oozes in the
north, and diatom oozes in the south. The content of organic C in the sediments varies in
different parts of the region but is generally no less than 0.3 % (by weight), Eh is characterized by negative or low positive values, and the oxygenated layer is either absent or of insignificant thickness (BEZRUKOV, 1964; LISITZIN, 1960). Both seston-feeding and detritusfeeding invertebrates are widely distributed in the macrobenthos of the eutrophic region.
As in shallow-water areas, their spatial distribution is determined by the food supply,
bottom relief and local rate of sedimentation. A detailed study of the distribution of
trophic groups was carried out in particular in the Bay of Bengal (SOKOLOVA and PASTERNAK, 1964), and it was possible to demonstrate a clear-cut succession of zones of predominant development of a certain type of feeding, with increasing depth and under the
effect of changing macrorelief and feeding conditions. A predominance of seston-feeders
in the lower part of the shelf is succeeded by a predominance of sorting detritophages on
the slope and indiscriminate detritophages in the depths of the central part of the bay.
Unlike the Pacific and the Atlantic Oceans, the Indian Ocean, owing to its position
in the tropical belt and in the southern temperate zone, has only one oligotrophic area.
This region occupies the southern parts of the Central Indian Basin, the Australian
Basin and the northern half of the Crozet Basin and coincides with the boundaries of a
southern subtropical gyre characterized by waters of extremely low productivity. This
part of the ocean is more than 3 800 - 4 000 m deep. The sediments in the northern
part of the oligotrophic region (down to latitudes 15 _17 0 S) are represented by radioliterally paved with them. The content of organic C in the sediments of the oligotrophic
oozes. Ferro manganese concretions are widespread here and in places the sea floor is
larian oozes and in the southern part by deep-sea red clays and carbonate-foraminiferan
area is 0.3 % or less, while En reaches high positive values. In the sediments of the northern
half of the region, minimum concentrations of humic acids were recorded, a fact which
is directly related to the low content of organic C (BORDOVSKY, 1964).
The macrobenthos of the oligotrophic region is characterized by a general quantitative
and qualitative impoverishment of bottom fauna; prevalent here are sestonophagous
invertebrates which feed on particulate matter from the bottom water layer, e.g. sponges,
cirripedes and polychaetes of the Serpulidae family. Detritus feeders which swallow
detritus together with the mud, such as holothurians, irregular sea-urchins or sea-stars
are entirely absent. In the trawl catches, the ratio by weight of seston-feeding to detritusfeeding invertebrates is expressed in values lower than unity, irrespective of the mesorelief.