Species composition of three size fractions of zooplankton used in routine monitoring of the Barents Sea ecosystem.

Hein Rune Skjoldal,Xabier Irigoien

doi:10.1093/plankt/fbab056

Hein Rune Skjoldal, Xabier Irigoien

Open Access

https://doi.org/10.1093/plankt/fbab056

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Abstract

Size fractionation with 2000 and 1000 μm screens is used by the Institute of Marine Research in Norway in routine monitoring of zooplankton biomass. This study examines the separation of taxa by this procedure. For copepods and cladocerans, the fractionation separates individuals according to their size in a consistent and predictable manner. Individuals up to 0.4 mm in width are contained in the small fraction (<1 mm). From width 0.4 to 0.8 mm, there is a progressive shift from the small to the medium fraction (1–2 mm). From about 0.8 mm width, individuals start to be contained in the large fraction (>2 mm). For Calanus finmarchicus, young copepodites CI–CIII are contained in the small fraction, while the older stages CV and adults are contained in the medium fraction. Small copepods (Oithona, Oncaea, Microcalanus, Pseudocalanus) are contained in the small fraction, as are most appendicularians and meroplanktonic invertebrate larvae. The large fraction includes large copepods, larger individuals of chaetognaths, krill and amphipods. The consistency of separation of taxa by size will help to interpret and improve the ecological relevance of results on size-fractioned zooplankton biomass in the Barents Sea as well as other high-latitude areas.

Highlights

Zooplankton as herbivores and omnivores provide the main link between phytoplankton primary production and planktivorous fishes and other consumers like seabirds and baleen whales in marine ecosystems (Skjoldal et al, 2004)
Calanus glacialis and C. hyperboreus were less abundant, by one and two orders of magnitude compared to C. finmarchicus
The biomass per individual was about 200, 60 and 10 μg dry weight for the large, medium and small fractions, respectively

Summary

Introduction

Zooplankton as herbivores and omnivores provide the main link between phytoplankton primary production and planktivorous fishes and other consumers like seabirds and baleen whales in marine ecosystems (Skjoldal et al, 2004). Zooplankton is commonly monitored to provide information on food and feeding conditions for pelagic planktivorous fish and to document changes in the ecosystem related to climate change and altered productivity The Institute of Marine Research (IMR) in Norway applies a standard method to monitor zooplankton, which involves determination of dry weight biomass in three size fractions. The method has been routinely used in monitoring in the Barents Sea since the mid-1980s (Skjoldal et al, 1992; Dalpadado et al, 2002, 2003, 2012, 2014; Stige et al, 2014) and in the Norwegian Sea since the early 1990s (Melle et al, 2004)

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