Agulhas Bank Plankton
195
progress. Their seasonal occurrence and predominant components over the Bank are
summarized in Table 1.
~
'"
.E
~
'"
::::
0
Table 1. Composition of phytoplankton blooms over the Agulhas Bank (1961-1967)
Spring
Summer
Autumn
Winter
Chaetoceros socialis
Chaetoceros socialis
Chaetoceros socialis
Chaetoceros socialis
most common inshore Nitschia pungens
C. curvisetus
most common in False
Other temperate
vaL atlantica
most common
Bay to Danger Point
Chaetoceros spp.,
inshore every summer
Dinoflagellates
Nitzschia seriata,
from False Bay to
Chaetoceros decipiens
N.pungens
Danger Point
Thalassiosira subtilis
var. atlantica
Rhizosolenia alata
more abundant further
fairly common
f. gracillima (oceanic)
east
east of Danger Point
Rhizosolenia alata
Rhizosolenia alata
Offshore blooms rare Dinoflagellates
(oceanic form)
f. gracillima (oceanic)
is main species in
Ceratium spp.
offshore blooms
Diatoms blooming exclusively
Bacteriastrum hyalinum
Coscinosira polychorda
Ditylum brightwelli
or predominantly over the Bank are the following:
Nitzschia closterium
Planktoniella sol
Rhizosolenia alata
R. alata f. gracillima
R. alata f. indica
R. hebetata f. semispina
R. styliformis
R. styliform is f. longispina
Inshore to the east of Cape Agulhas and in the offshore waters all over the Bank, the
dinoflagellates increase in numbers and diversity and a shift in the composition of the
diatom flora becomes obvious. A closer examination is needed to ascertain whether there
exists a typical bank community of phytoplankton. As yet, no clear boundaries between
floras have been determined.
The general impression gained from the phytoplankton data is that there is a strong
similarity between the inshore floras on either side of the Cape of Good Hope. The diatom
flora of the south coast shows predominantly Atlantic characteristics at least as far as
Cape Agulhas, and changes its character only gradually further to the East; blooms in
which species of the Benguela Current predominated have been recorded from as far as
East London (DE DECKER, 1962) .
III. Zooplankton
The monthly averages of zooplankton settled volumes show a general tendency
towards higher values over the Bank than off the west coast (Fig. 4). This may seem
paradoxical, considering the lower production of phytoplankton over the Bank. There
are also spectacular peak values in late spring or summer, far exceeding the corresponding
maxima off the west coast. The explanation is to be found in the perennial presence of
195
progress. Their seasonal occurrence and predominant components over the Bank are
summarized in Table 1.
~
'"
.E
~
'"
::::
0
Table 1. Composition of phytoplankton blooms over the Agulhas Bank (1961-1967)
Spring
Summer
Autumn
Winter
Chaetoceros socialis
Chaetoceros socialis
Chaetoceros socialis
Chaetoceros socialis
most common inshore Nitschia pungens
C. curvisetus
most common in False
Other temperate
vaL atlantica
most common
Bay to Danger Point
Chaetoceros spp.,
inshore every summer
Dinoflagellates
Nitzschia seriata,
from False Bay to
Chaetoceros decipiens
N.pungens
Danger Point
Thalassiosira subtilis
var. atlantica
Rhizosolenia alata
more abundant further
fairly common
f. gracillima (oceanic)
east
east of Danger Point
Rhizosolenia alata
Rhizosolenia alata
Offshore blooms rare Dinoflagellates
(oceanic form)
f. gracillima (oceanic)
is main species in
Ceratium spp.
offshore blooms
Diatoms blooming exclusively
Bacteriastrum hyalinum
Coscinosira polychorda
Ditylum brightwelli
or predominantly over the Bank are the following:
Nitzschia closterium
Planktoniella sol
Rhizosolenia alata
R. alata f. gracillima
R. alata f. indica
R. hebetata f. semispina
R. styliformis
R. styliform is f. longispina
Inshore to the east of Cape Agulhas and in the offshore waters all over the Bank, the
dinoflagellates increase in numbers and diversity and a shift in the composition of the
diatom flora becomes obvious. A closer examination is needed to ascertain whether there
exists a typical bank community of phytoplankton. As yet, no clear boundaries between
floras have been determined.
The general impression gained from the phytoplankton data is that there is a strong
similarity between the inshore floras on either side of the Cape of Good Hope. The diatom
flora of the south coast shows predominantly Atlantic characteristics at least as far as
Cape Agulhas, and changes its character only gradually further to the East; blooms in
which species of the Benguela Current predominated have been recorded from as far as
East London (DE DECKER, 1962) .
III. Zooplankton
The monthly averages of zooplankton settled volumes show a general tendency
towards higher values over the Bank than off the west coast (Fig. 4). This may seem
paradoxical, considering the lower production of phytoplankton over the Bank. There
are also spectacular peak values in late spring or summer, far exceeding the corresponding
maxima off the west coast. The explanation is to be found in the perennial presence of