Comparison of biomass and size-spectra derived from OPC data and net samples. Application to the assessment of mesoplankton distribution in the NW and N Iberian shelf
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AuthorsNogueira, E. (Enrique); González-Nuevo, G. (Gonzalo); Bode, A. (Antonio); Varela-Rodríguez, M. (Manuel); Morán, X.A.G. (Xosé Ánxelu Gutiérrez); Valdés-Santurio, L. (Luis)
Optical Plankton Counter
Data from vertical net hauls and from a submersible optical plankton counter (OPC) were compared in terms of biomass and slope of the normalized biomassesize spectra (NBeSS), a proxy for the size structure of the community. The relationship between the estimates of biomass in the overlapping range sampled by both methods (0.2e2 mm equivalent spherical diameter (ESD)) was linear and not significantly different to 1 (BOPC : BNET ¼ 1:1G0:1, r2 ¼ 0:84). However, the relationship varied depending on the size fraction considered; the ratio BOPC:BNET was 0:10G0:04 (r2 ¼ 0:30), 0:8G0:2 (r2 ¼ 0:66), and 2:4G0:5 (r2 ¼ 0:64) for the size fractions 0.2e0.5, 0.5e1, and 1e2 mm ESD, respectively. The discrepancies between methods were presumably due to the combined effect of the limitations of the instrument in the lower detection limit and the errors in the volume of water sampled by the net for the smallest size fraction, and to net avoidance enhanced by clogging for the largest size ...
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