Trans-Atlantic Study of Calanus: Regional and Seasonal Variability of feeding and reproduction

The objective of this subtask of the Trans-Atlantic
Study of Calanus (TASC) programme is to develop and
standardize methods to assess egg production from live
and preserved specimens. Establish the annual life and
reproductive cycle in different water masses in relation
to phytoplankton development and abiotic conditions.
Determine the influence of environmental variables on
feeding and reproduction.

The only data on the complete seasonal reproductive
cycle of C. finmarchicus are from 2 fjords (Diel and
Tande 1992, Plourde and Runge 1993). From more sporadic
measurements a strong regional variability of the
beginning of the spawning season, usually associated
with the spring bloom, has been observed, although
microzooplankton was shown to be an adequate substitute
for phytoplankton as a food source. It has been known
for a long time that C. finmarchicus can breed through
up to three generations per year, but the regional
variability of the number of generations is not at all
understood. The time series work at weathership "M" and
selected stations on cruises will be used for this work.
In order to cover a wide geographic range including the
open ocean, we will employ a combination of standardized
measurements of egg production from live specimens and
from preserved samples. To achieve this, an existing
method (Runge 1987) will be improved by including
histological preparations of the female gonad.

A strong discrepancy has been observed between
life-time fecundity of females fed in the laboratory
(Hirche 1991) and a fjord population (Diel and
Tande 1992), which laid only 20 % of the eggs spawned
by laboratory females. We will tackle this problem by
studying the effect of female condition, food quantity
and quality on egg production. The role of senescence
of females will also be investigated.

Grazing, female condition (CN and lipid composition,
gonad maturity) egg production (on shipboard and
preserved samples), hatching viability, and nauplii
survival will be determined.