Fróðskaparrit - 01.01.2005, Page 86

84 THE relative importance of protozooplankton and copepods as grazers
ON PHYTOPLANKTON DURING THE 1999 SPRING BLOOM ON THE FAROE SHELF
7°W
Figure 1. Topography and main
features of the flow field around
the Faroes. The two black dots with
letters beside them refer to sampling
stations. The broken line enclosing
the light gray area around the shelf
indicates the typical position of the
tidal front that separates the shelf
water from the open ocean.
east of Tórshavn (54 m bottom depth)
during a spring-bloom situation in 1999
(Fig. 1). Samples were taken on 13 cruis-
es from 19 April until 21 June. On each
cruise samples were taken for chlorophyll
a measurements, abundance and species
composition of phytoplankton, copepods
and protozooplankton, and egg production
by C. finmarchicus was obtained.
Water samples for chl a, phytoplankton
and protozooplankton species identifica-
tion were taken with 5 L Niskin bottles
at 2 and 20 m depth and preserved with
Lugol’s (final conc. 1%).
For measurements of chl a, duplicates (2
x 2 L) of seawater were filtered through a
Watman GF/C filter, and chl a concentra-
tion measured according to the method de-
scribed by Baltic Marine Biologists (1979)
with the modification that homogenization
was carried out using a Soniprep 140 ultra-
sound homogenizer. Chl a concentrations
were calculated according to the equation
of Jeffrey and Humprey (1975).
The phytoplankton samples were count-
ed and identified in 2, 5 or 10 mL sub-
samples after overnight settlement, using
an inverted microscope. Cell size of ap-
proximately 10 cells from each species/
genus was measured and converted to bio-
mass (cell carbon) using the equation for
diatoms from Menden-Deuer and Lessard
(2000) and the regression model for nano-
phytoplankton from Verity et al. (1992).
Protozooplankton (> lOpm) was counted
and identified in 50 mL subsamples after
overnight settlement, using an inverted mi-
croscope. Because of low cell concentra-