Fróðskaparrit - 01.01.2005, Side 89

LUTFALSLIGA AVIRKANIN AV PROTOZOOPLANKTON OG KOPEPODUM A VARBLOMING 37
AV PLANTUPLANKTON Á LANDGRUNNINUM í 1999
ton species composition was totally domi-
nated by diatoms. Especially Chaetoceros
spp. were abundant (Fig. 2, right). The
gelatinous colonial haptophyte Phaeocystis
pouchetii first appeared at the start of the
bloom, and increased much in abundance
towards the end of the research period.
Protozooplankton
The protozooplankton community consist-
ed of ciliates and heterotrophic dinoflagel-
lates. The ciliate community was totally
dominated by the genus Strombidium,
while the heterotrophic dinoflagellates
mainly consisted of the naked Gyrodin-
ium spp. and the thecate Protoperidinium
spp. The abundance and biomass of cili-
ates was low throughout the whole inves-
tigation, and showed no response to the
increase in phytoplankton biomass from
the pre-bloom to mid-bloom (Fig. 3 A and
B). The number of heterotrophic thecate
dinoflagellates was low during pre-bloom
but increased with a slight time lag com-
pared to the phytoplankton biomass (Fig.
3 C). This pattern is also reflected in the
biomass, which starts to increase shortly
after the initiation of the spring bloom
(Fig. 3 D).
There was no clear response in abun-
dance and biomass of naked heterotrophic
dinoflagellates to the increased phyto-
plankton biomass during the shift from
pre-bloom to mid-bloom.
The ingestion rate of the protozooplank-
ton community during pre-bloom was cal-
culated assuming that total loss rate was
due to copepod grazing and no prey selec-
tion by the copepods. Using these assump-
tions and the Calanus finmarchicus egg
production measurements for calculations
of the copepod grazing pressure on the
protozooplankton, yielded a growth rate
of 0.08 d'1 for the entire protozooplankton
community during pre-bloom.
During mid-bloom only the thecate
heterotrophic dinoflagellates showed a
response to the increased phytoplankton
standing stock. This response in the pe-
riod from 27 May until 17 June was used
to calculate a growth rate constant of 0.15
d'1 for the thecate heterotrophic dinoflag-
ellates.
The ciliates and the naked heterotrophic
dinoflagellates showed no response to the
increased phytoplankton standing stock.
Copepods
During pre-bloom the copepod communi-
ty consisted mainly of the neritic copepods
Pseudocalanus spp., Acartia longiremis
and Temora longicornis and the large oce-
anic copepod Calanus finmarchicus (Fig.
4A). In terms of biomass, it was totally
dominated by C. fimmarchicus (Fig. 4B),
which during this period constituted on
average 81 % of the total copepod biomass.
The category “other copepods” in Fig. 4A
includes Microcalanus sp., Centropages
typicus, Oithona similis and unidentified
copepods, mainly small stages of different
neritic copepods.
As the spring bloom progressed the
copepods increased in abundance reach-
ing a peak in early June, slightly after the
maximum in chl a concentration. This rise
in number of copepods is mainly due to
a rise in young stages i.e. nauplii and CI-