MEPS 204:143-157 (2000)  -  doi:10.3354/meps204143

A synoptic sampling method applied to Calanus finmarchicus population on the Norwegian mid-shelf in 1997

Ole-Petter Pedersen1,*, Kurt S. Tande1, Dag Slagstad2

1Norwegian College of Fishery Science, University of Tromsø, 9037 Tromsø, Norway
2Sintef Automatic, 7034 Trondheim, Norway

ABSTRACT: The majority of studies of marine processes are based on data from significant field efforts. This was also the case for the Trans-Atlantic Study of Calanus finmarchicus (TASC). Three cruises were conducted in 1997 as part of a field programme, covering the most important reproductive period of C. finmarchicus at the latitude of the Norwegian shelf. Conventional sampling provides distribution maps for selected life stages and species without taking into consideration errors introduced by internal rates of the biological components, behavior and advection. An understanding of physical-biological processes studied is best acquired by reconstructing a synoptic spatial distribution of plankton from samples including advective effects. We have developed a method for transforming conventionally sampled data into synoptic distributions (Synoptic Sampling Scheme, SSS transform) by removing the advective component. This is achieved by forward and backward Lagrangian particle tracking, both in physical xyz space and stage space. The method includes the application of hydrodynamical flowfields and physiological models featuring the population dynamics of C. finmarchicus. We have assessed the method by comparing and contrasting distribution maps based on untreated and normalised synoptic data on the demography of C. finmarchicus. The data were taken from 2 of the cruises conducted during the spring and summer of 1997 on the Norwegian mid-shelf sector. The results show that the lowest stages are more affected by the SSS transform than the older stages, due to shorter turnover time. Samples taken in regions with high current magnitudes contribute most to the reconfiguration of the cruise polygon. It is also shown that the SSS transform appears to have greater effects on small concentrations. The controlling factor is probably the fluxes amongst the stages. An effect indicated by the scheme is that the end regions will be most affected by the SSS, while the general ecological interpretations are not dramatically changed. Due to the effect advection and stage dynamics will have during the time of the cruise, the study recommends the use of new semi-synoptic sampling technology. This could eliminate the use of the SSS transform. To a certain extent the optical plankton counter (OPC) and acoustic Doppler current profiler (ADCP) could prove efficient in that context. Generally, interpretations based on uncorrected data should be made with extreme care.

KEY WORDS: Synoptic sampling · Calanus finmarchicus · Advection

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