252
T. S. S. &\0:
and the "Africana" cruises off South Africa (DE DECKER, 1973). At 32° S 100-112° E
there are 14 observations made by Australian scientists covering 8 months of the year.
The biomass at this station is very low and shows a bimodal fluctuation, high values
being observed during February and August (Fig. 9).
In the "African a" collections the biomass values are higher than at the 32 ° S -100 ° E
station, and variable (0.9 - 21. 7 ml for 100 m 3 ). Most of the stations here are located
on the continental shelf and the data here are excellent for correlation with hydrographical
parameters. A clear relationship exists between the prevailing current and the plankton
populations. Both copelata and chaetognaths come from the east and drift westwards
and southwards with the Agulhas Current.
II. Distribution of Copepoda
As the copepods form a good percentage of the zooplankton both in volume and
numbers, the pattern of distribution of biomass already described (IOBC, 1970 a),
reflects to a large extent the distribution of copepods and in fact many other groups
such as amphipods, chaetognaths, cladocerans, fish eggs and larvae, etc. In the Bay of
Bengal there is a high-density region in the head of the Bay during the SW monsOon
(April 16 - October 15) which disappears during the NE monsoon season. It is also clear
from these charts that the area of high density of the copepods spreads out from the area
of upwelling in the direction of the prevailing currents. Gaussia princeps (T. SCOTT)
studied by SARASWATHY (1973) reveals that this bathypelagic species exists in areas of
the Indian Ocean where intermediate waters come up within 200 m of the surface.
Haloptilus acutifrons (GIESBRECHT) studied by ROSAMMA and SARALADEVI (personal
communication) considered to be a deep water species, presents a pattern of distribution
suggesting that it is euryphagous, eurythermal and euryhaline and was taken in stations
where the O 2 was not less than 1.5 mll- 1 and seems to avoid salinities higher than 36%0.
III. Decapod Larvae
The total distribution of decapod larvae (IOBC, 1970 a) shows the interesting feature
that while off the Somali, Indian and Burmese coasts high numbers (301- 900 per haul)
occur adjacent to the coast, off Saudi Arabia they occur at a great distance (150-200
miles) from the shore. They are also distributed much more extensively during the SW
monsoon than in the NE monsoon. The occurrence of a dense patch of larvae south of
Java (over 2,700 per haul) and a large patch of high value (300-2,700) south of the
Andaman is noteworthy.
Very high concentrations of the larvae are met with at one station each in the western
and eastern Indian Ocean, off Port Elizabeth and south of Java respectively, and 3 stations
off the west coast of India (mostly brachyuran larvae). In the central Indian Ocean south
of 10° S latitude there is very little representation of these larvae in the plankton.
The larvae of penaeid prawns show a maximum concentration around the southern
extremity of the Indian peninsula and off the Somali coast. Similar patterns of distribution
are found for other families of decapod larvae.
T. S. S. &\0:
and the "Africana" cruises off South Africa (DE DECKER, 1973). At 32° S 100-112° E
there are 14 observations made by Australian scientists covering 8 months of the year.
The biomass at this station is very low and shows a bimodal fluctuation, high values
being observed during February and August (Fig. 9).
In the "African a" collections the biomass values are higher than at the 32 ° S -100 ° E
station, and variable (0.9 - 21. 7 ml for 100 m 3 ). Most of the stations here are located
on the continental shelf and the data here are excellent for correlation with hydrographical
parameters. A clear relationship exists between the prevailing current and the plankton
populations. Both copelata and chaetognaths come from the east and drift westwards
and southwards with the Agulhas Current.
II. Distribution of Copepoda
As the copepods form a good percentage of the zooplankton both in volume and
numbers, the pattern of distribution of biomass already described (IOBC, 1970 a),
reflects to a large extent the distribution of copepods and in fact many other groups
such as amphipods, chaetognaths, cladocerans, fish eggs and larvae, etc. In the Bay of
Bengal there is a high-density region in the head of the Bay during the SW monsOon
(April 16 - October 15) which disappears during the NE monsoon season. It is also clear
from these charts that the area of high density of the copepods spreads out from the area
of upwelling in the direction of the prevailing currents. Gaussia princeps (T. SCOTT)
studied by SARASWATHY (1973) reveals that this bathypelagic species exists in areas of
the Indian Ocean where intermediate waters come up within 200 m of the surface.
Haloptilus acutifrons (GIESBRECHT) studied by ROSAMMA and SARALADEVI (personal
communication) considered to be a deep water species, presents a pattern of distribution
suggesting that it is euryphagous, eurythermal and euryhaline and was taken in stations
where the O 2 was not less than 1.5 mll- 1 and seems to avoid salinities higher than 36%0.
III. Decapod Larvae
The total distribution of decapod larvae (IOBC, 1970 a) shows the interesting feature
that while off the Somali, Indian and Burmese coasts high numbers (301- 900 per haul)
occur adjacent to the coast, off Saudi Arabia they occur at a great distance (150-200
miles) from the shore. They are also distributed much more extensively during the SW
monsoon than in the NE monsoon. The occurrence of a dense patch of larvae south of
Java (over 2,700 per haul) and a large patch of high value (300-2,700) south of the
Andaman is noteworthy.
Very high concentrations of the larvae are met with at one station each in the western
and eastern Indian Ocean, off Port Elizabeth and south of Java respectively, and 3 stations
off the west coast of India (mostly brachyuran larvae). In the central Indian Ocean south
of 10° S latitude there is very little representation of these larvae in the plankton.
The larvae of penaeid prawns show a maximum concentration around the southern
extremity of the Indian peninsula and off the Somali coast. Similar patterns of distribution
are found for other families of decapod larvae.