166
F. J. R. TAYLOR:
in the Bay of Bengal at this time of the year. The presence of many species considered by
previous authors to be deep-water "shade forms" in the upper waters in the eastern
parts of the Bay of Bengal and adjacent to the Andaman and Nicobar Islands was in
contrast to the rest of the material. This aspect will be discussed further later in this
paper.
There were striking increases of dinoflagellates in the eastern Bay of Bengal off
Vishakhapatnum and particularly off Madras (stations 99 to 103). An exceptionally
large number of taxa were present at the latter. At station 103 a total of 88 dinoflagellate
taxa were recorded, the highest for a single station in the author's experience. Directly
over the narrow shelf the proportion of diatoms increased somewhat and the number of
dinoflagellate taxa diminished.
The long cruise V (55 0 E and 75 0 E meridians plus an Arabian Sea line to the Gulf
of Aden) showed a much more discontinuous distribution of dinoflagellates than was
apparent on the other meridional cruises. The Arabian Sea line exhibited only moderate
amounts of preservable dinoflagellates, indicating that thecate dinoflagellates played
a minor role in the exceptionally high primary productivity recorded by the "Anton
Bruun" south of the Arabian coast. Instead, the relevant samples (from stations 284- 287)
contained large amounts of small, unrecognizably preserved cells, coccolithophorids and
amorphous detritus. The dominant dinoflagellate here and in the Gulf of Aden was
Pyrocystis pseudonoctiluca.
On the 55 0 E meridian amounts fluctuated greatly with moderate numbers off the
Somali coast and an abrupt increase at station 294, immediately to the north of the
Seychelles Platform. At the southernmost station on the 55
0
E meridian, station 306, very
large amounts of detritus were present with only low concentrations of net plankton
and very few dinoflagellates. Below 30 0 S all stations had very few dinoflagellates although
diatoms were moderately abundant in the Subtropical Convergence Region close to the
Islands of Amsterdam and St. Paul. The only dinoflagellates showing moderate increases
close to this region were Cladopyxis brachiolata and Ceratium falcatiforme on the 75 0 E
meridian. Samples rich in dinoflagellates were found to the south of India on the 75 0 E
meridian (stations 325 to 327), dominated chiefly by Pyrocystis pseudonoctiluca. The
only species showing moderate abundance in the South Equatorial Current was Ceratium
trichoceros.
In summary, during and immediately following the NE monsoon the Bay of Bengal
and Andaman Sea show only a reduced river influence but a rich dinoflagellate flora.
In the open Indian Ocean dinoflagellates amounts fluctuated strongly, with maximum
numbers close to the Seychelles Platform on the right edge of the Equatorial Counter
Current which flows close to the north of the bank during this season. Large numbers
were also present to the south of India at stations either in the North Equatorial Current
or between it and the Equatorial Counter Current. Southern stations were generally
poor in dinoflagellates.
4. Shade Flora
In 1900, in CHUN's book on deep-water marine life, SCHIMPER introduced the
idea of a "Schattenflora" in plankton, consisting of certain photosynthetic species living
typically below 50 or 100 m, structurally and physiologically adapted to low light concen-
F. J. R. TAYLOR:
in the Bay of Bengal at this time of the year. The presence of many species considered by
previous authors to be deep-water "shade forms" in the upper waters in the eastern
parts of the Bay of Bengal and adjacent to the Andaman and Nicobar Islands was in
contrast to the rest of the material. This aspect will be discussed further later in this
paper.
There were striking increases of dinoflagellates in the eastern Bay of Bengal off
Vishakhapatnum and particularly off Madras (stations 99 to 103). An exceptionally
large number of taxa were present at the latter. At station 103 a total of 88 dinoflagellate
taxa were recorded, the highest for a single station in the author's experience. Directly
over the narrow shelf the proportion of diatoms increased somewhat and the number of
dinoflagellate taxa diminished.
The long cruise V (55 0 E and 75 0 E meridians plus an Arabian Sea line to the Gulf
of Aden) showed a much more discontinuous distribution of dinoflagellates than was
apparent on the other meridional cruises. The Arabian Sea line exhibited only moderate
amounts of preservable dinoflagellates, indicating that thecate dinoflagellates played
a minor role in the exceptionally high primary productivity recorded by the "Anton
Bruun" south of the Arabian coast. Instead, the relevant samples (from stations 284- 287)
contained large amounts of small, unrecognizably preserved cells, coccolithophorids and
amorphous detritus. The dominant dinoflagellate here and in the Gulf of Aden was
Pyrocystis pseudonoctiluca.
On the 55 0 E meridian amounts fluctuated greatly with moderate numbers off the
Somali coast and an abrupt increase at station 294, immediately to the north of the
Seychelles Platform. At the southernmost station on the 55
0
E meridian, station 306, very
large amounts of detritus were present with only low concentrations of net plankton
and very few dinoflagellates. Below 30 0 S all stations had very few dinoflagellates although
diatoms were moderately abundant in the Subtropical Convergence Region close to the
Islands of Amsterdam and St. Paul. The only dinoflagellates showing moderate increases
close to this region were Cladopyxis brachiolata and Ceratium falcatiforme on the 75 0 E
meridian. Samples rich in dinoflagellates were found to the south of India on the 75 0 E
meridian (stations 325 to 327), dominated chiefly by Pyrocystis pseudonoctiluca. The
only species showing moderate abundance in the South Equatorial Current was Ceratium
trichoceros.
In summary, during and immediately following the NE monsoon the Bay of Bengal
and Andaman Sea show only a reduced river influence but a rich dinoflagellate flora.
In the open Indian Ocean dinoflagellates amounts fluctuated strongly, with maximum
numbers close to the Seychelles Platform on the right edge of the Equatorial Counter
Current which flows close to the north of the bank during this season. Large numbers
were also present to the south of India at stations either in the North Equatorial Current
or between it and the Equatorial Counter Current. Southern stations were generally
poor in dinoflagellates.
4. Shade Flora
In 1900, in CHUN's book on deep-water marine life, SCHIMPER introduced the
idea of a "Schattenflora" in plankton, consisting of certain photosynthetic species living
typically below 50 or 100 m, structurally and physiologically adapted to low light concen-