Intercomparison of five nets used for mesozooplankton sampling

Abstract

Intercomparison of nets commonly used for mesozooplankton sampling in the Black and Mediterranean seas was attempted within the SESAME (Southern European Seas: Assessing and Modelling Ecosystem Changes) project. Five nets were compared: three Juday nets equipped with 150 μm, 180 μm and 200 μm mesh size, a Nansen net (100 μm mesh size) and a WP2 (200 μm mesh size). Replicated samples were taken at one station in the western Black Sea offshore waters in April 2009. The samples were analyzed at species level (except for meroplankton), stages (for copepods) and body length was measured for all organisms. A decrease of total abundance values was observed with increasing mesh size, due to the significantly higher numbers of animals smaller than 1 mm in the samples obtained using fine mesh size rather than with coarser nets. Few comparisons were revealed significant as regards the abundance of 1-2 mm long animals, while no significance was detected for specimens larger than 2 mm. The above differences resulted in discripancies between nets as regards species and stage composition. Biomass values did not differ significantly between nets, due to the important contribution of the large animals (Calanus euxinus) to total biomass. The smallest and the largest animals revealed high variability between replicates collected using the Nansen, Juday-200 μm and WP2 nets. Correction factors were calculated for the conversion of abundance values between each pair of nets. The differences observed between nets regarding abundance and biomass, community taxonomic composition and size structure, as well as the estimated correction factors, provide useful information for the harmonization of data obtained using the above nets in the Black Sea.

Seasonal Variability in the Zooplankton Community Structure in a Sub-Arctic Fjord as Revealed by Morphological and Molecular Approaches

“…Consequently, their abundances and the species richness between November 2018 and April are not directly comparable with the rest of the study. There is however little evidence that larger copepods and older life stage of smaller copepods (including copepodites stage CIII-adults of Calanus and Pseudocalanus) are caught less efficiently with a mesh size of 64 µm compared to 180 µm (e.g., Nichols and Thompson, 1991;Di Mauro et al, 2009;Altukhov et al, 2015;Chen et al, 2016). Thus, we are confident that the seasonal patterns we observed in the morphological data are not severely biased by the change in mesh size, especially when we take the change of mesh size into consideration in our data interpretation.…”

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“…A zooplankton net with >200 µm mesh could be more suitable for small-sized copepod sampling, especially for the genera Oithona (Calbet et al, 2001, Altukhov et al, 2015. Although the mesh size of zooplankton net used for sampling in this study was not very suitable for small-sized copepods, high numbers of Oithona spp.…”

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“…While small planktonic marine oithonids exist ubiquitously in World Ocean (Paffenhöfer, 1993), the assessment of zooplankton using sampling technique with the mesh size larger than (or equal to) 150 µm resulted in a serious undervaluation of their abundance (Altukhov et al, 2015;Dahms, Tseng & Hwang, 2015;Hwang, Kumar, Dahms, Tseng & Chen, 2007), misunderstanding of their role in trophic interactions in the sea (Turner, 2004) and of their grazing impact on phytoplankton primary production. Small marine cyclopoid Oithona davisae Ferrari and Orsi, 1984, is a typical neritic copepod (Uchima, 1988), which occasionally occurring high abundances in estuarine and coastal areas (Hirota, 1990;Nishida, 1985).…”