Fróðskaparrit - 01.01.2005, Page 87

LUTFALSLIGA ÁVIRKANIN AV PROTOZOOPLANKTON OG KOPEPODUM Á VÁRBLÓMING 35
AV PLANTUPLANKTON Á LANDGRUNNINUM í 1999
tion all cells in the subsample were count-
ed (on average 25-30 ciliates and 35-40
dinoflagellates). Each cell was measured
and converted to biomass (cell carbon)
using the equation for dinoflagellates and
aloricate ciliates from Menden-Deuer and
Lessard (2000).
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. The ingestion rate of
the protozooplankton during this period is
thus estimated from the calculated cope-
pod ingestion rate during pre-bloom (us-
ing both copepod egg production and the
temperature dependent production method
from Huntley and Lopez (1992)). During
mid-bloom the growth rate constant p of
the thecate heterotrophic dinoflagellates
was calculated using the increase in bio-
mass during mid-bloom: p = [ln(Bt/B0)]/
t, where Bc = biomass at the beginning of
the period, Bj = biomass at the end, and t
= length of the time interval (days). Inges-
tion was calculated using a gross growth
efficiency of 40% (Hansen et al., 1997).
Copepods were sampled in vertical hauls
from 50 m depth to the surface using a
200 pm mesh size WP-2 net. The volume
filtered was measured with a Hydro Bios
flow meter with back run stop attached to
the net opening. A total of 3 replicate tows
were taken on each cruise. Towing speed
was 1/3-1/2 m s'1. The samples were pre-
served in 4% buffered formaldehyde. In
the laboratory, sub-samples of 300-400
animals were taken using a Motoda cyl-
inder splitter, identified and counted. The
cephalothorax length was measured on
each copepod (total length for nauplii and
non copepods), and biomass (pgC ind'1)
was calculated using length/weight regres-
sions derived from the literature specified
for each group: Calanus finmarchicus
(Hirche and Mumm, 1992); Pseudocala-
nus spp., Temora spp. and Centropages
spp. (Klein Breteler et al., 1982); Acartia
spp. (Berggreen et al., 1988); Microcala-
nus spp. and Oithona spp. (Sabatini and
Kiørboe, 1994).
For egg production measurements of
C. finmarchicus, live females were col-
lected using a 200 pm mesh size WP-2-net
equipped with a 2 L non-filtering cod-end.
Healthy females (n = 10-13) were incubat-
ed individually at in situ temperature and
dim light in false bottom containers (mesh
size 400 pm) containing approximately 1
L of 60 pm filtered seawater. Incubation
period was 24 h. After incubation, the
eggs were filtered through a 30 pm mesh
net and counted. Female cephalotorax and
the diameter of 5-10 eggs were measured.
Female carbon content was calculated ac-
cording to length-weight regressions from
Hirche and Mumm (1992). Assuming a
carbon: DW of 0.6, egg carbon was calcu-
lated using a volume to carbon conversion
of 0.14 x 10'6 pgC pm"3 (Kiørboe et al.,
1985).
The ingestion rate of the copepod com-
munity was estimated according to egg
production in C. finmarchicus females.
Egg production was converted to biomass
specific production rates (P/B), and inges-
tion rate was calculated for the entire co-
pepod community using a gross growth