|Secondary production of Calanus finmarchicus (Copepoda: Calanoidea) in a transitional system of the Fladen Ground area (northern North Sea) during the spring of 1983|
Fransz, H.G.; Diel, S. (1985). Secondary production of Calanus finmarchicus (Copepoda: Calanoidea) in a transitional system of the Fladen Ground area (northern North Sea) during the spring of 1983, in: Gibbs, P.E. (Ed.) Proceedings of the 19th European Marine Biology Symposium, Plymouth, Devon, UK, 16-21 September 1984. pp. 123-133
In: Gibbs, P.E. (Ed.) (1985). Proceedings of the 19th European Marine Biology Symposium, Plymouth, Devon, UK, 16-21 September 1984. Cambridge University Press: Cambridge. ISBN 0-521-30294-3. 541 pp., more
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From 30 April to 24 May 1983, zooplankton samples were collected every third day with a towed sampler at the depth intervals 0-20, 20-60, and 60-100 m near a drifting drogue in the Fladen Ground area. The drogue followed the horizontal drift of the upper 25 m. The samples were used to determine the numerical abundance of the 12 developmental stages of Calanus finmarchicus, the main herbivore in this area in spring. For the estimation of growth and development the copepodite stages I, IV and V were selected from living samples collected with a vertical net and incubated for 3 days in deck containers on board. Normal, concentrated, or partly-filtered sea water was used to simulate different food levels. The same stages were also incubated for 3 days in situ in gauze-windowed Plexiglass containers which were suspended from the drifter system at various depths. In addition, the development of a cohort was studied under laboratory conditions. During the sampling period, the drogue and most of the Calanus population drifted 40 miles in northerly direction. The carbon biomass ranged from 0.2 to 1.7 9 m-2 and showed peaks on 9 May and 21 May, with a sharp decline after the first. At the end of the period, high biomass values were observed at the position where the drifter system was launched originally. Rates of development and growth of incubated stages decreased after the first week, presumably due to changes in phytoplankton composition. Carbon production was only 1.2 9 m-2 in 27 days, mainly produced by copepodites III and IV. The results suggest that most of the Calanus biomass found in the Fladen Ground area is not locally produced. A possible source of Calanus are the frontal systems east of Orkney and eastern Scotland: Calanus patches may be transported by the Fair Isle current and other residual currents into the Fladen Ground area, which then forms a transition zone between frontal and stratified areas.