dc.description.abstract | During the summers of l979 and 1980, ecological investigations
were carried out in the marginal ice zone in the Barents Sea. In
the investigation an attempt is made to follow the development of
the production processes, from nutrients via phytoplankton and
zooplankton to capelin, in order to map the feeding conditions
for the capelin and its variations. The methods used in the field
work and most of the results obtained during the two summer
seasons are presented by ELLERTSEN -et -al. (1981). In the present
report we discuss and summarize the field results so far and
compare them with the results from a model.
The results show a close relationship between ice melting and
recession and a phytoplankton bloom occurring at the ice edge. It
seems that the decrease in salinity in the upper few meters due to
ice melting produce a sharp increase in water stability. Thereby
favourable conditions are created for an intense phytoplankton
bloom. This bloom seems to occur somewhat earlier than the spring
bloom in the areas of the Barents Sea not covered by ice, where
water stability is mainly influenced by the warming of the upper
layers.
Zooplankton development follows very close that of the phytoplankton,
with a bloom starting near the ice edge. The biomass was
found to increase with the distance from the edge. This tendency is
most clear in the upper layers, where the zooplankton spawning and
the development of the zooplankton larvae occur.
The main bulk of the zooplankton consisted of the copepod Calanus
finmarchicus. The most numerous species was the small copepod
Oithona similis.
There was a change in age composition of -C. finmarchicus with the
distance from the ice, the nauplii and the younger copepodite
stages predominating in the north.
The younger stages (I-III) were most abundant in the surface layer
where they had hatched earlier in the year, while the older
stages (IV-V and adult females) had overwintered and predominated
in the deeper layer.
The stomach contents of 12-18 cm capelin from several stations
were investigated. The stomach filling seemed to be related to the
plankton density in the sea, with highest filling in areas with
much plankton. The species composition in the stomachs roughly
corresponded with the plankton composition, with a tendency to a
higher numeric percentage of euphausiids and chaetognaths in the
stomachs than in the plankton. Near half of the contents, as
weight, consisted of calanoid copepods, while the euphausiids,
chaetognaths and amphipods made up 30, 10 and 6 per cent of the
weight respectively.
A model describing the growth of phytoplankton and zooplankton
along a north-south section in the Barents Sea is also briefly
described. Using ice map data obtained via satellite, several
simulation runs have been performed. The dynamics of the phytoplankton
growth seems to agree with what we believe it should
according to the available data. However, some discrepancies
indicate areas that should be further investigated in order to
increase our knowledge and improve the model. The zooplankton
part of the model produces results that are more questionable.
Variations in zooplankton biomass are reasonably calculated
whereas the stage distribution does not fit our data. Reasons for
this are discussed. | en |