B. Niehoff et al., A high frequency time series at Weathership M, Norwegian Sea, during the 1997 spring bloom: the reproductive biology of Calanus finmarchicus, MAR ECOL-PR, 176, 1999, pp. 81-92
The reproductive biology of Calanus finmarchicus was investigated at a perm
anent station in the Norwegian Sea (Weathership Stn M, 66 degrees N, 2 degr
ees E) during a time series between March and June 1997. The temporal devel
opment of female abundance, egg production rate and gonad development stage
in relation to the phytoplankton production cycle is described. Abundance
of females, copepodite stage 5 and males as well as female gonad morphology
were examined from WP2 net samples taken daily from the upper 100 m. Daily
egg production rate and number of spawning females were determined from 50
individual females placed in multiwells or beakers. Once a week a multinet
haul from 1000-500-250-100-50-0 m was performed to study the depth distrib
ution of females and gonad development stages. Results show that the reprod
uctive period of C. finmarchicus in the Atlantic region of the Norwegian Se
a can be subdivided in 3 periods in relation to phytoplankton development:
(1) During the prebloom over a period of 49 d mean egg production rate was
8 eggs female(-1) d(-1) and an average of 47 % of the females were mature.
(2) Coincident with the bloom in mid May the egg production rate increased
up to a maximum of 44 eggs female(-1) d(-1) while more than 80 % of the fem
ales were mature. (3) After the bloom at the beginning of June, egg product
ion decreased, and mature females were only rarely found. Feeding experimen
ts indicate that food quantity limited egg production prior to the bloom, w
hile presumably food quality was not sufficient during postbloom. However,
due to high female abundance the total population egg production prior to t
he bloom was the same as during the bloom. This implies that the reproducti
on of C. finmarchicus in the Norwegian Sea is to some extent decoupled from
the phytoplankton bloom.