Trans-Atlantic Study of Calanus: Latitudinal Differences in population dynamics: Mesocosm Studies

The objective of this subtask of the Trans-Atlantic Study of Calanus (TASC)
programme is to identify the environmental cues governing the life cycle
pattern along a latitudinal gradient from 60 to 70 degrees N along the
Norwegian coast.

A two year cultivation study of C. finmarchicus from eggs to adults will be
conducted. We will compare and contrast responses in growth pattern,
developmental and mortality schedules to variations in physical settings among
cohorts from two geographically distinct populations. These populations should
potentially have different history and physiological adaptations. Eggs from a
northern (Grotsund, 70 degrees N) and from a southern population
(Trondheimsfjorden, 63 degrees N) will be obtained at the two sites, and
brought to one mesocosm site. We will perform two such experiments - one in
1996 and one in 1997. The hatched nauplii, from the two sites, will be raised
in triplicates, in parallel mesocosm in the northern site during the first
year, and in the southern site during the next year. The mesocosms will be run
for the period from March to June/July. The Ho hypothesis will thus be that
there is no differences in growth pattern, developmental and mortality
schedules among the two geographical distinct populations of C. finmarchicus.

Cylindric mesocosms (50 m3) arranged around a platform nearby Karvika Research
Station in Tromso, will be filled with FSW, and stocked with Calanus eggs, and
a composite natural phytoplankton community, generated from spores in sediment
samples form the area. After Day 30 additional stocks of flagellates will be
added in order ensure a high quality diet for the intensive growth period
during the copepodite stages (see Berggreen et al. 1988; Hansen et al. 1994).
Light conditions in the mesocosms will be set equal to 10 m of depth by
maintaining a light filtering net on to of each mesocosm. The food conditions,
temperature and salinity will be monitored daily. Parameters like temperature,
chlorophyll, particulare organic carbon (Infra Red Gas Analyser), C/N, species
composition of phytoplankton and microzooplankton will be monitored weekly.
Copepod samples will be obtained weekly by a plankton net (100 and 180 mm
mesh), staged, weighed and stored for later lipid analysis. Sex
differentiation, signs of diapause entry and the degree of moulting success to
a second generation will be studied by gonad examination of the cohorts under
study.