Some Patterns of the Distribution of Bottom Fauna in the Indian Ocean
473
The passage from eutrophic to oligotrophic conditions proceeds gradually with the
decrease of organic matter precipitated on the sea floor and the slowing down of the
rate of sedimentation. Under transitional trophic conditions the unevenness in the
distribution of trophic groups increases as compared with eutrophic regions, notwithstanding the similarity of the mesorelief.
III. Some Remarks on the Biogeography of Bottom Invertebrates
in the Indian Ocean
There have been no recent detailed studies of the distribution of zoogeographical
complexes in the coastal shallow-water areas of the Indian Ocean. The results of
faunistic investigations carried out in 1966 on board the "Academician Knipovitch"
merely added some details to the widely known scheme of EKMAN (1935) and revealed
that within the Indo-West-Pacific area the zoogeographical boundary lies on the shelf of
western India, located at about the latitude of Nova Goa. This boundary coincides
with the northern limit of the penetration of equatorial waters onto the shelf of western
India (ELIZAROV, 1968). Here the ranges of a number of species of bivalve and gastropod
molluscs living in the shallow-water areas of the western and eastern parts of the
Indian Ocean, come together. Further on, beyond the shelf of India, this limit seems to
run along the Laccadive Islands. In any case, the penaeids of the western Indian Ocean
and some other invertebrates do not spread northward and westward of this limit
(STAROBOGATOV, in print). According to this author, endemic species must exist among
the penaeids inhabiting the whole extent of the shelf between Nova Goa and the Straits
of Malacca. As regards the zoogeographical zonation of the abyssal region, the analysis
of the geographical distribution of some hundred species of invertebrates living in
depths of more than 2 000 m has shown that the deep-sea fauna of the Indian Ocean is
less self-contained than that of the Pacific and the Atlantic Oceans. It is not integral,
and species common to the northern and southern parts of the ocean are not numerous.
The dissociation of the fauna increases with increasing depth of habitat. An important
part is played in the deep-sea benthos of the nothern half of the Indian Ocean by species
common to the Pacific (nearly 50%); in the southern part of the Indian Ocean antarctic
forms predominate (nearly 80%), and among the broadly eurybathic forms are those
common to the Atlantic (VINOGRADOVA, 1962).
VINOGRADOVA assigns the northern part of the Indian Ocean, as a sub-region, to the
Pacific-North-Indian deep-sea region and its southern part, as an Indian province, to the
Antarctic-Indo-Pacific sub-region of the Antarctic deep-sea region.
473
The passage from eutrophic to oligotrophic conditions proceeds gradually with the
decrease of organic matter precipitated on the sea floor and the slowing down of the
rate of sedimentation. Under transitional trophic conditions the unevenness in the
distribution of trophic groups increases as compared with eutrophic regions, notwithstanding the similarity of the mesorelief.
III. Some Remarks on the Biogeography of Bottom Invertebrates
in the Indian Ocean
There have been no recent detailed studies of the distribution of zoogeographical
complexes in the coastal shallow-water areas of the Indian Ocean. The results of
faunistic investigations carried out in 1966 on board the "Academician Knipovitch"
merely added some details to the widely known scheme of EKMAN (1935) and revealed
that within the Indo-West-Pacific area the zoogeographical boundary lies on the shelf of
western India, located at about the latitude of Nova Goa. This boundary coincides
with the northern limit of the penetration of equatorial waters onto the shelf of western
India (ELIZAROV, 1968). Here the ranges of a number of species of bivalve and gastropod
molluscs living in the shallow-water areas of the western and eastern parts of the
Indian Ocean, come together. Further on, beyond the shelf of India, this limit seems to
run along the Laccadive Islands. In any case, the penaeids of the western Indian Ocean
and some other invertebrates do not spread northward and westward of this limit
(STAROBOGATOV, in print). According to this author, endemic species must exist among
the penaeids inhabiting the whole extent of the shelf between Nova Goa and the Straits
of Malacca. As regards the zoogeographical zonation of the abyssal region, the analysis
of the geographical distribution of some hundred species of invertebrates living in
depths of more than 2 000 m has shown that the deep-sea fauna of the Indian Ocean is
less self-contained than that of the Pacific and the Atlantic Oceans. It is not integral,
and species common to the northern and southern parts of the ocean are not numerous.
The dissociation of the fauna increases with increasing depth of habitat. An important
part is played in the deep-sea benthos of the nothern half of the Indian Ocean by species
common to the Pacific (nearly 50%); in the southern part of the Indian Ocean antarctic
forms predominate (nearly 80%), and among the broadly eurybathic forms are those
common to the Atlantic (VINOGRADOVA, 1962).
VINOGRADOVA assigns the northern part of the Indian Ocean, as a sub-region, to the
Pacific-North-Indian deep-sea region and its southern part, as an Indian province, to the
Antarctic-Indo-Pacific sub-region of the Antarctic deep-sea region.