Fróðskaparrit - 01.01.2005, Page 95

LUTFALSLIGA ÁVIRKANIN AV PROTOZOOPLANKTON OG KOPEPODUM Á VÁRBLÓMING 93
AV PLANTUPLANKTON Á LANDGRUNNINUM í 1999
rate of 0.08 d'1 is based on a relatively high
estimated ingestion rate from the copepod
community during pre-bloom. This high
estimated ingestion rate from the copepod
community, can be interpreted in two dif-
ferent ways:
1. The first possibility is that primary
production during pre-bloom actually
could have been high during this pe-
riod, but due to grazing a build up of
biomass was prevented.
2. The second possibility is that the
copepod community during pre-bloom
partly relies on lipid reserves to fuel
gonad development and egg produc-
tion.
There has been some speculation in the past
years as to what extent copepods are able
to control the onset of the phytoplankton
spring bloom. Yin et al. (1997) reported
on the importance of the large oceanic co-
pepod Neocalanus plumchrus during early
spring from the Strait of Georgia, British
Columbia. A large biomass of this cope-
pod prior to spring-bloom, was able to
suppress and thus delay the spring bloom
development. Bathmann et al. (1990)
found a large influence of copepods on the
spring-bloom development in the Norwe-
gian Sea, and postulated that if the upward
migration of overwintering copepods oc-
curred shortly before or concomitant with
the diatom spring bloom, bloom forma-
tion could be hindered. Other researchers
have, however, stated the opposite, and
concluded that the grazer community is
not able to control or postpone a spring
bloom (e.g. Smith et al., 1985; Hirche
et al., 1991; Nielsen and Hansen, 1995).
It is, however, not likely that the cope-
pods were suppressing the phytoplank-
ton spring bloom during our study. If the
grazer community actually was suppress-
ing the development of the phytoplankton
spring bloom, we would have expected C.
finmarchicus to graze at a maximum, and
hence show a much higher egg production
rate during this period.
The most likely possibility for the high
estimated ingestion rates during pre-bloom
is probably that the females may have
used stored lipids to fuel parts of the egg
production during this period. There has
been some debate about the importance of
lipid storages during low productive pre-
bloom periods. It is generally accepted
that gonadogenesis and development of
early oocyte in many Calanus species is
partly fuelled by stored energy during
winter (e.g. Hirche, 1996 and references
therein), but to what extent these lipid re-
serves actually are used for egg produc-
tion in C. finmarchicus is not certain. This
has been proposed for the closely related
species Calanus helgolandicus (Gatten et
al., 1979; 1980), and Hirche (1996) sug-
gested that overwintering C. finmarchicus
females might invest their lipid storages in
egg production, since they may not have
undergone the reported drastic lipid losses
solely for maturing from the CV copepo-
dite stage. This is supported by investiga-
tions in the Faroe-Shetland Channel and
northern North Sea (Richardson et al.,
1999), the Labrador Sea (Cabal et al.,
1997) and at station M in the Norwegian