280
M. VANNUCClandD. NAVAS:
1. Bay of Bengal
Although we would not go as far as to say that the Bay of Bengal is nothing more
than a large estuary, it has many of the features of an estuary: its surface waters have
high temperature and low salinity, the latter decreasing northward and, together with
the subsurface water, have twice as many species restricted to them as the surface and
subsurface waters of the Arabian Sea. About half are neritic species, elsewhere confined
to coastal areas of greater or lesser extent. They are found in the Bay of Bengal as far out
to sea as their longevity and the velocity of the current permit. All are metagenetic species,
and therefore dependent on available substratum for the benthic-living hydroid stage; all
have a long life span and are restricted to salinity lower than 35%0 associated with
temperature higher than 19 - 20 0 C.
2. Arabian Sea
The Arabian Sea surface system has temperatures higher than 19 - 20° C, associated
with salinity higher than 35,8%0. VANNUCCI and SANTHAKUMARI (in press) have listed
14 species that are new records for the Arabian Sea, 4 of them already known from the
Bay of Bengal. The other 10 species add to the known difference in the hydromedusan
fauna in the surface layers of the Arabian Sea and Bay of Bengal. The species common
to the surface layers of both are found in restricted coastal and estuarine areas in the
Arabian Sea, except for a few very euryhaline species.
3. The Indian Ocean Central Water
This system, for the present purpose, comprises waters with temperatures lower than
19 - 20° C and salinity of about 34.5 - 36.0%0. The species found therein occur also in
Arabian Sea subsurface water, but only species that can tolerate lower salinity are
found in the Bay of Bengal subsurface water too (salinity 34.1- 35.00/00). These species
are geographically widely distributed and may include some preferring cold water ~s
well as Antarctic species, either in upwelling areas or at the lower boundary.
4. Upwelling
Examples are scarce, but some species such as Ectopleura sacculifera appear to be
restricted to upwelling areas. However, we cannot yet generalize on the correlation
between upwelling and particular species.
5. Deep and Intermediate Waters
There are deep- or intermediate-water species that do not appear to be of Antarctic
origin, like Merga reesi and Amphogona apicata. There are also several Antarctic species
that sink at the convergences and spread north via Antarctic intermediate water or
Antarctic deep water and thence into Indian Ocean central water, Arabian Sea intermediate water, Arabian Sea subsurface water and Bay of Bengal subsurface and deep
water, as far as their limits of tolerance will permit. These include Euphysora furcata,
M. VANNUCClandD. NAVAS:
1. Bay of Bengal
Although we would not go as far as to say that the Bay of Bengal is nothing more
than a large estuary, it has many of the features of an estuary: its surface waters have
high temperature and low salinity, the latter decreasing northward and, together with
the subsurface water, have twice as many species restricted to them as the surface and
subsurface waters of the Arabian Sea. About half are neritic species, elsewhere confined
to coastal areas of greater or lesser extent. They are found in the Bay of Bengal as far out
to sea as their longevity and the velocity of the current permit. All are metagenetic species,
and therefore dependent on available substratum for the benthic-living hydroid stage; all
have a long life span and are restricted to salinity lower than 35%0 associated with
temperature higher than 19 - 20 0 C.
2. Arabian Sea
The Arabian Sea surface system has temperatures higher than 19 - 20° C, associated
with salinity higher than 35,8%0. VANNUCCI and SANTHAKUMARI (in press) have listed
14 species that are new records for the Arabian Sea, 4 of them already known from the
Bay of Bengal. The other 10 species add to the known difference in the hydromedusan
fauna in the surface layers of the Arabian Sea and Bay of Bengal. The species common
to the surface layers of both are found in restricted coastal and estuarine areas in the
Arabian Sea, except for a few very euryhaline species.
3. The Indian Ocean Central Water
This system, for the present purpose, comprises waters with temperatures lower than
19 - 20° C and salinity of about 34.5 - 36.0%0. The species found therein occur also in
Arabian Sea subsurface water, but only species that can tolerate lower salinity are
found in the Bay of Bengal subsurface water too (salinity 34.1- 35.00/00). These species
are geographically widely distributed and may include some preferring cold water ~s
well as Antarctic species, either in upwelling areas or at the lower boundary.
4. Upwelling
Examples are scarce, but some species such as Ectopleura sacculifera appear to be
restricted to upwelling areas. However, we cannot yet generalize on the correlation
between upwelling and particular species.
5. Deep and Intermediate Waters
There are deep- or intermediate-water species that do not appear to be of Antarctic
origin, like Merga reesi and Amphogona apicata. There are also several Antarctic species
that sink at the convergences and spread north via Antarctic intermediate water or
Antarctic deep water and thence into Indian Ocean central water, Arabian Sea intermediate water, Arabian Sea subsurface water and Bay of Bengal subsurface and deep
water, as far as their limits of tolerance will permit. These include Euphysora furcata,