High reproduction of Calanus finmarchicus during a diatom-dominated spring bloom
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Feeding, egg production, hatching success and early naupliar development of Calanus finmarchicus were measured in three north Norwegian fjords during a spring bloom dominated by diatoms and the haptophyte Phaeocystis pouchetii. Majority of the copepod diet consisted of diatoms, mainly Thalassiosira spp. and Chaetoceros spp., with clearance rates up to 10 ml ind−1 h−1 for individual algae species/groups. Egg production rates were high, ranging from ca 40 up to 90 eggs f−1 d−1, with a hatching success of 70–85%, and fast naupliar development through the first non-feeding stages. There was no correlation between the egg or nauplii production and diatom abundance, but the hatching success was slightly negatively correlated with diatom biomass. However, the overall high reproductive rates suggested that the main food items were not harmful for C. finmarchicus reproduction in the area, although direct chemical measurements were not conducted. The high population egg production (>1,20,000 eggs m−2 d−1) indicated that a large part of the annual reproduction took place during the investigation, which stresses the importance of diatom-dominated spring phytoplankton bloom for population recruitment of C. finmarchicus in these northern ecosystems.
KeywordsDinoflagellate Spring Bloom Hatching Success Selective Feeding Spring Phytoplankton Bloom
I wish to thank Paul Wassmann for the organisation of the cruise, and P. Wassmann and Christian Wexels Riser for providing the unpublished data on chlorophyll-a, inorganic nutrients, phytoplankton species composition, copepod abundance and copepod faecal pellet production. Elena Arashkevich, Sigrun Jónasdóttir, Serge Poulet and C. Wexels Riser kindly commented the previous versions of the manuscript. Jörg Dutz assisted with the sampling and sorting of copepods. This study was financially supported by Academy of Finland, Carlsberg Foundation and a mobility grant from Nordic Academy for Advanced Study (NorFA), and was conducted during a cruise of the EU-project BIOHAB.
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