Measuring copepod abundance in deep‐water winter habitats in the NE Norwegian Sea: intercomparison of results from laser optical plankton counter and multinet

Abstract

The main purpose of this study was to assess the usefulness of the laser optical plankton counter (LOPC) as a Calanus finmarchicus monitoring tool in the NE Norwegian Sea in winter. To test this, a multinet and an LOPC were used simultaneously to sample overwintering copepods in the Lofoten basin in January 2007. Additional data from an LOPC laboratory experiment were also analyzed to help the interpretation of the field data. Both the laboratory data and the field data indicated that the presence of particles other than zooplankton generally contaminated the zooplankton signal in the LOPC data. However, reliable abundance estimates could be made from the LOPC data by choosing an appropriate size range in the LOPC size distribution. This size range was determined by comparing LOPC abundance estimates from systematically varying size ranges to multinet zooplankton abundance data. The average difference was smallest for a size range of about 900-1500 lm. As C. finmarchicus, stages IV and V, was by far the most abundant species in the NE Norwegian Sea, abundance estimates from the LOPC in this size range were in practice estimates of C. finmarchicus abundance, making the LOPC suitable as a tool for providing high resolution winter data in the NE Norwegian Sea.

Springtime zooplankton size structure over the continental shelf of the Bay of Biscay

“…The comparison between abundance estimates derived from different sampling approaches renders contrasting results. Total counts from net catches are generally lower than or equal to those observed by in situ particle counters (González-Quirós and Checkley, 2006;Schultes and Lopes, 2009;Gaardsted et al, 2010), and this difference was attributed mainly to fragile aggregates and detritus that are often not analyzed in net catches but also disaggregated by the net passage and thus not correctly sampled (e.g., González-Quirós and Checkley, 2006). Fragile gelatinous zooplankton can also be destroyed by passage through the net and may also partially account for the difference between in situ particles counters and net catches.…”

Capturing quantitative zooplankton information in the sea: Performance test of laser optical plankton counter and video plankton recorder in a Calanus finmarchicus dominated summer situation

“…The Laser-OPC (LOPC) was introduced as the second generation of 38 the OPC in the beginning of the new millennium to provide broader ranges in sizes and 39 abundance estimates than the OPC, and also to provide information on the morphology 40 of zooplankton (Herman et al 2004). Recently, the LOPC has successfully been used 41 to assess copepod abundance and size structures in deep water overwintering habitats 42 (Gaardsted et al 2010). The LOPC has also provided data to analyse processes within 43 mesozooplankton communities based on biovolume spectra ), but its 44 potential as a diagnostic tool in surface waters during summer remains to be established.…”

“…85 % (Gaardsted et al 2010 We analysed the effect of marine snow on the abundance of different zooplankton size showed the same tendencies as both the Multinet and the LOPC (Table 1).…”

“…In addition to the size range applied in our 289 study, we applied three different size ranges from recent studies analysing abundance of 290 C. finmarchicus (Herman and Harvey 2006;Checkley et al 2008;Gaardsted et al 2010).…”

Large versus small zooplankton in relation to temperature in the Arctic shelf region

“…This method is especially valuable in areas where the abundance of zooplankton is relatively large and dominated by few species, because it allows taxonomic species distributions to be determined in the different size groups recorded by the LOPC. This is especially true in north Atlantic and Arctic waters, where studies based on optical plankton counters were able to distinguish Calanus species Gaardsted et al 2010;Trudnowska et al 2014).…”