Agulhas Bank Plankton
205
for both species in the same period: it started in January from the east and south, and
ended up NW of the Cape of Good Hope in October, when a new population would
appear also in the east.
Seasonal peaks in abundance are very much in evidence in many species, although
they are not always repeated in both years. It is probable that the anomalous conditions
of January 1965 affected the cycle of certain species. Only Fritillaria formica had its
peak in January, in both years. April saw the culmination, mainly over the Bank, of
Fritillaria haplostoma, Stegosoma magnum and Oikopleura cornutogastra, and in the
western sector, of Megalocercus huxleyi and Oikopleura rufescens, all five species in
both years; Tectillaria fertilis and Oikopleura intermedia had a peak in April 1964 only.
In July of both years 4 species culminated: Oikopleura albicans, O. parva, O. cophocerca
and Fritillaria borealis. The following 4 species had a peak in October 1964 of 1965,
but none in both years, and they also showed more or less important maxima in other
seasons, as indicated in parentheses:
Fritillaria pellucida (April 1964, Jan. and Oct. 1965)
Oikopleura dioica (July 1964, Oct. 1965)
O. fusiformis (April 1964, Oct. 1965)
O.longicauda (April and Oct. 1964)
The seasonal maxima observed in SE Australian waters by THOMPSON (1948) for
the individual species show very little correspondence with those in South Africa, but
analogous hydrological events in Australian and South African waters do not take place
at the same time of the year.
3. Chaetognatha
HEYDORN (1959), working on one year's monthly samples which covered most of the
area off the west coast between Cape Town and Lamberts Bay, listed 12 species of
chaetognaths. STONE (1969) found 18 species in the course of his investigation of the
chaetognath community of the Agulhas Current. Among his 34 station positions equally
spaced along 8 transects of the current between Durban and Plettenberg Bay, 5 were
located on the eastern wing of the Agulhas Bank. His list comprised all the species found
by HEYDORN off the west coast.
Chaetognath studies are currently pursued by MASSON and encompass the whole
routine survey area, bridging the gap between the regions investigated by HEYDORN and
STONE, respectively. Only 6 months' material (May to October 1964) has been examined
so far and the results can be summarized as follows.
The species list (Table 5) has been expanded to 24 species, comprising all those found
by HEYDORN (1959) and by STONE (1969). The most striking feature so far observed has
been the close relationship of the different chaetognaths to the different water masses.
Sagitta friderici, the most common chaetognath in this region and considered by many
authors as a neritic species, was indeed found mainly in inshore waters in May, June and
July. A small number were also distributed offshore over the Agulhas Bank, indicating
that their distribution may be related to depth. In August, September and October, however, a number of S. friderici moved offshore along the west coast, due probably to a corresponding movement of the surface water taking place in conjunction with inshore
upwelling. This interpretation is supported by the fact that Eukrohnia hamata and
S. decipiens, both relatively deep-water chaetognaths, were found in the surface water
205
for both species in the same period: it started in January from the east and south, and
ended up NW of the Cape of Good Hope in October, when a new population would
appear also in the east.
Seasonal peaks in abundance are very much in evidence in many species, although
they are not always repeated in both years. It is probable that the anomalous conditions
of January 1965 affected the cycle of certain species. Only Fritillaria formica had its
peak in January, in both years. April saw the culmination, mainly over the Bank, of
Fritillaria haplostoma, Stegosoma magnum and Oikopleura cornutogastra, and in the
western sector, of Megalocercus huxleyi and Oikopleura rufescens, all five species in
both years; Tectillaria fertilis and Oikopleura intermedia had a peak in April 1964 only.
In July of both years 4 species culminated: Oikopleura albicans, O. parva, O. cophocerca
and Fritillaria borealis. The following 4 species had a peak in October 1964 of 1965,
but none in both years, and they also showed more or less important maxima in other
seasons, as indicated in parentheses:
Fritillaria pellucida (April 1964, Jan. and Oct. 1965)
Oikopleura dioica (July 1964, Oct. 1965)
O. fusiformis (April 1964, Oct. 1965)
O.longicauda (April and Oct. 1964)
The seasonal maxima observed in SE Australian waters by THOMPSON (1948) for
the individual species show very little correspondence with those in South Africa, but
analogous hydrological events in Australian and South African waters do not take place
at the same time of the year.
3. Chaetognatha
HEYDORN (1959), working on one year's monthly samples which covered most of the
area off the west coast between Cape Town and Lamberts Bay, listed 12 species of
chaetognaths. STONE (1969) found 18 species in the course of his investigation of the
chaetognath community of the Agulhas Current. Among his 34 station positions equally
spaced along 8 transects of the current between Durban and Plettenberg Bay, 5 were
located on the eastern wing of the Agulhas Bank. His list comprised all the species found
by HEYDORN off the west coast.
Chaetognath studies are currently pursued by MASSON and encompass the whole
routine survey area, bridging the gap between the regions investigated by HEYDORN and
STONE, respectively. Only 6 months' material (May to October 1964) has been examined
so far and the results can be summarized as follows.
The species list (Table 5) has been expanded to 24 species, comprising all those found
by HEYDORN (1959) and by STONE (1969). The most striking feature so far observed has
been the close relationship of the different chaetognaths to the different water masses.
Sagitta friderici, the most common chaetognath in this region and considered by many
authors as a neritic species, was indeed found mainly in inshore waters in May, June and
July. A small number were also distributed offshore over the Agulhas Bank, indicating
that their distribution may be related to depth. In August, September and October, however, a number of S. friderici moved offshore along the west coast, due probably to a corresponding movement of the surface water taking place in conjunction with inshore
upwelling. This interpretation is supported by the fact that Eukrohnia hamata and
S. decipiens, both relatively deep-water chaetognaths, were found in the surface water