Diel and seasonal v a n a t~o n s in the vertical distnbut~ons of Calanus finmarchicus Metrjd~a longa M lucens and C h~r~d l u s armatus in Malangen, northern Norway, were determined from F e b~ uary until December 1992 The vertical behav~our differed among the species and among the ditterent stages of a single species The vertical distnbution of C hnmarchlcus was d o m~n a t e d by seasonal rather than d~e l vertical migrat~on, and this species was found in surface waters during the spring phytoplankton bloom (March to May) and at the bottom of the fjord in the fall and wlnter Melrldla spp were generally cons~stent d~e l vertical mlgrators However M longa usually stayed deeper and had a larger migration dmplltude than M lucens M longa was more deeply dlstrlbuted In the w~n t e r than d u r~n g the summer while M lucens showed no such seasonal trend The vertical behaviour of C d~m a t u s was related to the seasonal change In day length and diel vert~cal ~nlgratlon was strong In periods of large d a y h i g h t contrast (spring and autumn) but ceased d u r~n g the p e r~o d s of m~d n~g h t sun and wlnter darkness Duiing the summer C armatus stayed d e e p both day and night D~e l vertlcal b e h a v~o u r in young stages of all 4 species was weak or undetectable by the s a m p l~n g method used Younger stages of C finn~archlcus and Metrld~a spp remained higher in the water column, tvhile the opposite was observed In C armatus While seasonal v a n a t~o n s in vertical behaviour a r e related to v a n a t~o n s in food and light condltlons ~n t e rand intraspecific differences may be due to life h~story diet and suscept~bil-~t y to predation
Population dynamics of Calanus finmarchicus have been modelled using very finely divided representation of the stock accord~ng to age-within-stage, in the manner of models developed by C. S. Davis, A. Sciandra, F. Carlotti and others. A key assumption of the model is that development rate is relatively insensitive to food-limitation, so that stage duration can be represented by a temperature function alone. We used the Belehradek function for this purpose, noting that better data are needed for fitting its parameters. The model closely simulates the timing of stage progression and relative stage abundances of C. finmarchicus in the Malangen fjord system (northern Norway) during the winter-spring generation. The model 1s sensitive to the resolution of the age-within-stage division, but it is fully stable at 0.5 h increments. Modifications of the model simulated several methods for field estimation of stage duration in Calanus (or other highly seasonal copepod populations). A method based on changes in stage proportions (the 'Heinle graph' method) is biased by confounding of the effects of developmental progress and mortality on stage proportions. However, the model shows that the bias is mild and the method gives useful estimates of stage duration. Simulation of a method based on molting rate deterrninations ('Kirnmerer experiments') showed its unsuitability for highly seasonal stocks In which stage composition is changing rapidly. Differences in C. finmarchicus survivorship schedules between constant and continuously increasing temperatures were simulated, showing that such differences in pattern are critical to annual survival and stock production. Simple methods for fitting mortality rates to data using the model were extremely sensitive to sampling noise. More complex methods may succeed but remain to be developed.
The marine copepod Calanus finmarchicus from coastal areas of northern Norway was cultivated a t 3 temperatures from e g g to adult in the laboratory. Growth and survival of copepodite stages were markedly affected by the temperature regime. If populations of copepodite Stage I experience a sharp decrease in temperature, mortality rate is increased. On this basis the hypothesis is formulated that during the main annual growth penod of C. finn~archicus in arctic-boreal areas not only is this specles sensihve to a temperature decrease, but also a certain temperature increase IS a prerequisite to successful growth from copepodite Stage I to copepodite Stage IV and V. The ecological implications of this hypothesis are discussed. Temperature-dependent mortality rates in certain growth periods of C. finmarchrcus are also related to the postulated rule of equiproportional development in marine copepods.
A production model for the herbivorous arctic copepod Calanus glacialis is presented. The model combines data on growth rates obtained from energy balance studies with population structure data gathered during the arctic productive period. A 2 yr life cycle suggests that the species is present in the plankton as 2 main year classes, thus enabling it to utilize the short annual spring bloom during both spawning and the intensive growth period from CIV to CV This pattern of life cycle should reduce the probability of food limitation during spawning and during periods of high lipid deposition as from CIV to CV A tentative assessment of total annual production is calculated to 8.4 g C m-' with a maximum of 0.16 g C m-2 d-' during August. PIB ratios calculated from balance experiments ranged from 0.03 to 0.05 during July. Results from sensitivity analysis are presented in order to highlight especially important ecological aspects of this species in the arctic environment.
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