402
M. SAKTHIVEL:
northern part of the Arabian Sea is borne out by previous and present findings. There
were also 268 zooplankton collections from north of 10° N in the Bay of Bengal, none
of which contained this species. The southern boundary of S. subula in the South Indian
Ocean further supports previous findings in all 3 oceans. Clearly, the boundary of
subtropical convergence which runs for the most part between 38 ° Sand 40 ° S acts as a
thermal barrier to the distribution of S. subula further south than 4Q ° S.
S. subula is more common between 5° Nand 30° S, especially in the subtropical gyre,
the Mozambique Channel and along 110° E in the Indian Ocean. It is abundant off the
Somali coast, and in 2 isolated patches in the eastern equatorial area and another at
16 1.0 total
8 20
"S
~
O~ ____ ~-L~~-LLL~-LLL~-L~
day
..
0 ........
7 . . . 0 . . _ •
...... :. \
/
' 'q.
/ .
. ...
/r.~
Fig. 2. Latitudinal and diurnal variation of the occurrence of Styliola subula in the Indian Ocean
19° Sand 100° E, also in the areas between 66° E and 80° E, and 10° Sand 25° S (Fig. 1).
The 3 larger areas of abundance are known to have mild climatic conditions.
Even though the area of abundance near the Somali coast is very close to the Equator,
it is subject to upwelling which reduces the temperature to the subtropical level. The
other 2 large areas are between 10° and 25° S. The availability of adequate food in
association with mild climate must provide a suitable habitat for the breeding and
spawning of this species.
From the records of S. subula in the HOE collections an attempt was made to evaluate
the latitudinal variation in the occurrence of this species. The percentage occurrence
at each 5° interval was calculated by dividing the number of records by the number of
collections. The abundance in the form of arithmetic mean at each 5 ° interval was
estimated by dividing the total number of individuals by the number of records. As this
M. SAKTHIVEL:
northern part of the Arabian Sea is borne out by previous and present findings. There
were also 268 zooplankton collections from north of 10° N in the Bay of Bengal, none
of which contained this species. The southern boundary of S. subula in the South Indian
Ocean further supports previous findings in all 3 oceans. Clearly, the boundary of
subtropical convergence which runs for the most part between 38 ° Sand 40 ° S acts as a
thermal barrier to the distribution of S. subula further south than 4Q ° S.
S. subula is more common between 5° Nand 30° S, especially in the subtropical gyre,
the Mozambique Channel and along 110° E in the Indian Ocean. It is abundant off the
Somali coast, and in 2 isolated patches in the eastern equatorial area and another at
16 1.0 total
8 20
"S
~
O~ ____ ~-L~~-LLL~-LLL~-L~
day
..
0 ........
7 . . . 0 . . _ •
...... :. \
/
' 'q.
/ .
. ...
/r.~
Fig. 2. Latitudinal and diurnal variation of the occurrence of Styliola subula in the Indian Ocean
19° Sand 100° E, also in the areas between 66° E and 80° E, and 10° Sand 25° S (Fig. 1).
The 3 larger areas of abundance are known to have mild climatic conditions.
Even though the area of abundance near the Somali coast is very close to the Equator,
it is subject to upwelling which reduces the temperature to the subtropical level. The
other 2 large areas are between 10° and 25° S. The availability of adequate food in
association with mild climate must provide a suitable habitat for the breeding and
spawning of this species.
From the records of S. subula in the HOE collections an attempt was made to evaluate
the latitudinal variation in the occurrence of this species. The percentage occurrence
at each 5° interval was calculated by dividing the number of records by the number of
collections. The abundance in the form of arithmetic mean at each 5 ° interval was
estimated by dividing the total number of individuals by the number of records. As this