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

Abstract

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.

Hydrodynamic model forecasts as a guide for process studies on plankton and larval fish

“…On Georges Bank and the Norwegian shelf this has been performed for the zooplanktonic organism Calanus finmarchicus (Miller et al. , 1998; Pedersen et al ., 2001; Pedersen and Tande, 2000). In the North Sea, this has been performed for herring (Bartsch et al.…”

Hydrodynamic backtracking of fish larvae by individual-based modelling

“…At first sight, the issue of tracing backwards the state of a larval sample in time appears simple: just advect larvae in a direction opposite the currents and shrink their size by the same amount as their growth, if time is running forward (Pedersen et al 2000, Allain 2004); however, dispersion processes are present in the ocean and must be considered, as we will show later, because otherwise we have no information on the error margin in results and further simple backtracking opposite current lines may contain an error bias, since dispersion processes in the ocean are not spatially uniform. Batchelder (2006) similarly found that diffusion cannot be ignored in backtracking.…”

A possible connection between hydrography and the distribution of Calanus finmarchicus on the Norwegian midshelf in 1997

“…in all samples from that station, even if only CV and adult C. finmarchicus were observed in other depth strata. The procedure for separating the species is described in detail in Pedersen et al (2000). The huge quantity of data collected during the cruises has been condensed, and we have extracted only a limited amount for publication.…”

“…The huge quantity of data collected during the cruises has been condensed, and we have extracted only a limited amount for publication. Visualization of the data is presented as 3D stack plots, and a cubic spline method is applied, along with a method combining Laplacian interpolation and splines (see Pedersen et al, 2000, for further details).…”