Trans-Atlantic Study of Calanus: Culture Experiments on nutrition, growth and reproduction

The objective of this subtask of the Trans-Atlantic Study of Calanus (TASC)
programme is to define the biochemical components of the diet needed for
Calanus growth and reproduction and to determine, using laboratory cultures,
how growth, egg production, and egg viability vary with the diversity of diet.

This subtask will establish cultures of C. finmarchicus, using material
collected in the field programme, and will build on experience with C.
helgolandicus, cultures of which are currently maintained over multiple
generations at PML. This approach will provide relevant information for
understanding life cycle phenomena and contribute to the calibration and
validation of the population dynamics model (subtask 14). The culture facility
will provide a central resource for TASC, both for studying behavioural
mechanisms determining life history strategy, and enable new biochemical and
molecular techniques to be evaluated under controlled conditions, before
deployment in the field programme. In addition the laboratory culture
experiments will address aspects of overwintering physiology based on
suggestions from the field programme. The effect of environmental variables
will be considered and the aim will be to mimic multi-generation Calanus
population dynamics in the laboratory. It is an ultimate goal to have both
sibling species in simultaneous culture, enabling critical comparative
physiological studies to be made under defined conditions.

An increased effort in nutritional biochemistry, particularly lipid
biochemistry, exploring the dietary links between Calanus and its food
environment will significantly advance understanding of the relationships
between diet and production. Dietary diversity is expected to enhance
production. Recognising the importance of omnivory (Kleppel, 1993), new
approaches are needed to establish relations between food quantity and quality,
and development rate and egg production. It is well established that lipids
play a vital role in the life history strategies of polar organisms (Sargent et
al., 1993). However, it is poorly understood: a) how environmental variables
determine the production of lipids in the marine environment and hence the
availability to C. finmarchicus, b) the rate at which dietary lipid is
ingested/assimilated by C. finmarchicus and/or biosynthesised in the field, c)
if, in some circumstances, the availability of essential dietary lipids in the
marine environment affects the growth and reproduction of Calanus. Optimal
growth and egg production by Calanus requires an adequate food composition;
some essential fatty acids, for example, cannot be synthesised by copepods. It
is not clear whether the natural food environment is generally adequate in
dietary terms, or whether Calanus spp. are sometimes limited by food
composition in nature as opposed to food concentration. This needs to be
determined; it is important to establish whether fecundity is driven by food
characteristics, and to incorporate this critical linkage in models. This
component of TASC will interact strongly with the proposed field programme, by
providing key analytical and shipboard (weathership "M") experimental input to
TASC cruises, and also by testing, under defined laboratory conditions,
critical hypotheses generated by the field programme.

Controlled culture experiments under defined regimes will be combined with
detailed lipid and molecular analysis, and population dynamics and modelling.