Fróðskaparrit - 01.01.2005, Qupperneq 93

LUTFALSLIGA AVIRKANIN AV PROTOZOOPLANKTON OG KOPEPODUM A VARBLOMING 9]
AV PLANTUPLANKTON Á LANDGRUNNINUM í 1999
chain forming diatoms, hence also Cha-
etoceros spp.
The ciliate community did not respond to
the phytoplankton bloom. Like in the case
of the naked heterotrophic dinoflagellates,
the lack of response could be attributed to
their feeding mechanism. A prey/preda-
tor relationship of approximately 1:10 in
cell diameter has been shown for ciliates
(Fenchel, 1986; Jonsson, 1986; Hansen et
al., 1994), which renders a diatom bloom
dominated by large chain forming species
of little value for most ciliates.
The copepod community showed a clear
response to the phytoplankton bloom,
peaking in abundance shortly after the chl
a maximum in early June. The species
composition was consistent with previous
investigation on the Faroe Shelf (Gaard,
1999) with the presence of key species like
Pseudocalanus spp., Acartia longiremis,
Temora longicornis and Calanus finmar-
chicus. Of these, C. finmarchicus made up
the bulk of the zooplankton biomass dur-
ing both pre- and mid-bloom. However,
the advection of this oceanic species onto
the shelf is highly variable between years
(Gaard and Hansen, 2000), but once on
the shelf, it has a great influence on the
shelf ecosystem (Gaard and Steingrund,
2001). The response to the bloom is also
seen in the development stage composition
of C. finmarchicus, which shows a distinct
shift towards younger stages (nauplii-CHI)
during mid-bloom (Fig. 4C).
However, using a WP-2 net with a rnesh
size of 200 pm will not sample small cope-
pod species like Oithona similis and nau-
plii and small copepodite stages of most
larger copepod species representatively.
Even the smallest stages of the large cope-
pod like C. finmarchicus will not be sam-
pled quantitatively using this course mesh
size (Nicols and Thompson, 1991; Munk
et al., 2003)
Grazing and carbon flow
In calculating the copepod community
grazing impact on the phytoplankton
standing stock, we have to consider proto-
zooplankton as a potential food resource.
In the past years it has been shown that es-
pecially during periods of low production,
protozooplankton may be an important
food resource for copepods (e.g. Ohman
and Runge, 1994; Levinsen et al., 2000).
The abundance, and thus the importance
of protozooplankton as food for the cope-
pods, varied over the study period. Dur-
ing pre-bloom the biomass of protozoo-
plankton made up more than 40% of the
phytoplankton biomass. However, as the
spring bloom started to develop the pro-
tozooplankton biomass likely became less
important as it was diluted by the two or-
ders of magnitude higher phytoplankton
biomass.
Pre-bloom
As mentioned above the biomass of proto-
zooplankton was about half of the phyto-
plankton biomass during pre-bloom. As-
suming no prey selection by the copepods,
the protozooplankton rnust have made up
a substantial part of their diet during this
period. This was taking into account when
calculating the copepod grazing impact on
the phytoplankton standing stock.