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analysis.
The zooplankton material used for this thesis was sampled between the
2nd and the 6th of February in the equatorial Atlantic at 15 stations
located on a profile, which ran along from 3° N to 2° S at a longitude
of 22° W. At all stations five standard depth intervals (300m to 200m,
200m to 100m, 100m to 50m, 50m to 25m and 25m to the surface) were
vertically sampled with a multiple opening and closing net of lOOym
mesh size.
The fixed sample material was size- fractioned for image analysis and
the largest fraction was pre- sorted under a stereomicroscope to
dissemble aggregates of organisms.
The vertical distribution of copepods reflects water column stratification
caused by a strongly marked thermocline that was located between
50m and 100m. The bulk of copepods is situated in the mixed upper
layer with a clear maximum in the region between 25m and the surface.
Below the thermocline the numbers of copepods are comparatively low
with a slight increase in the region between 200m and 300m.
The mean biomass of 23 10^ ppm and the structure of the vertical
distribution of copepods in the upper 100m are comparable with findings
from the oligotrophic regions of the anti cyclonic gyres on both
sides of the equator. This conformity meets the expectations of a normal
seasonal development in the investigation area.
The slight increase in copepods between 200m and 300m is attributed
to an active transport by meridional ciculation cells as indicated by
the distribution of the total amount of copepods and the structure of
the size- frequency- distributions. However the influence of seasonal
vertical migration cannot be excluded.
The vertical distribution of copepods does not indicate changes that
can be explained by diurnal vertical migrations.
Accounting for 17% of the total abundance nauplii occur in negligible
number. It is assumed that reproduction is limited by the poor food
suppley. On the other hand it is possible that the meshsize of lOOyra
is not sufficiently fine for a quantitative collection of nauplii.
The wrigglers are represented by Hicrosetella sp..The composition of
the samples indicates that the harpacticoid copepod uses aggregates