142 S. Z. EL-SAYED and H. R. JITIS: Phytoplankton Production in the Southeastern Indian Ocean
standing stock and primary production were also noted at stations 4 and 18, located
just to the north and to the south of the Polar Front, respectively. Whether the high
biological productivity of the latter stations is related to their proximity to the Antarctic
Convergence with its concomitant hydrographic effects, is not clear.
The effect of the Polar Front on the distribution of the nutrient salts is quite noticeable
from the data collected during this cruise, e.g. N03 - -N values at stations 2 and 4, north
of the Polar Front, were 0.3 and 10.8 ,ug-at I-I, compared to 21.1 and 24.7 ,ug-at I-I,
at stations 5 and 8 located south of the Front. In general, higher concentrations of
nutrients were found south of the Polar Front than north of it, with conspicuous increases from north to south as the Convergence was crossed.
The effect of the Polar Front was also noticeable with regard to the species composition
of the phytoplankton at the stations occupied. Analysis of the phytoplankton samples
collected has shown that the dinoflagellates constituted an important component of
the phytoplankton at the stations occupied north of the Polar Front (mainly species
of Ceratium and Peridinium). South of the Polar Front, the diatoms were the dominant
element in the phytoplankton. Of the 88 species of diatoms identified, the 10 most
frequently encountered species were: Asteromphalus hookeri, Chaetoceros atlanticum,
C. dichaeta, Corethron criophilum, Dactyliosolen antarcticus, Eucampia balaustium,
Fragilariopsis kerguelensis, Rhizosolenia alata f. inerme, R. hebetata f. semispina, and
Thalassiothrix antarctica. A more detailed account will be published of the effect of the
Polar Front on the distribution and abundance of the phytoplankton.
standing stock and primary production were also noted at stations 4 and 18, located
just to the north and to the south of the Polar Front, respectively. Whether the high
biological productivity of the latter stations is related to their proximity to the Antarctic
Convergence with its concomitant hydrographic effects, is not clear.
The effect of the Polar Front on the distribution of the nutrient salts is quite noticeable
from the data collected during this cruise, e.g. N03 - -N values at stations 2 and 4, north
of the Polar Front, were 0.3 and 10.8 ,ug-at I-I, compared to 21.1 and 24.7 ,ug-at I-I,
at stations 5 and 8 located south of the Front. In general, higher concentrations of
nutrients were found south of the Polar Front than north of it, with conspicuous increases from north to south as the Convergence was crossed.
The effect of the Polar Front was also noticeable with regard to the species composition
of the phytoplankton at the stations occupied. Analysis of the phytoplankton samples
collected has shown that the dinoflagellates constituted an important component of
the phytoplankton at the stations occupied north of the Polar Front (mainly species
of Ceratium and Peridinium). South of the Polar Front, the diatoms were the dominant
element in the phytoplankton. Of the 88 species of diatoms identified, the 10 most
frequently encountered species were: Asteromphalus hookeri, Chaetoceros atlanticum,
C. dichaeta, Corethron criophilum, Dactyliosolen antarcticus, Eucampia balaustium,
Fragilariopsis kerguelensis, Rhizosolenia alata f. inerme, R. hebetata f. semispina, and
Thalassiothrix antarctica. A more detailed account will be published of the effect of the
Polar Front on the distribution and abundance of the phytoplankton.