Trophic relationships and the role of Calanus in the oceanic ecosystems south and north of Iceland

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The aim of this study was to increase the knowledge on the role of Calanus copepods and trophic relations of the key components of the oceanic ecosystems south-west (Atlantic waters) and north (Arctic and sub-Arctic waters) of Iceland. The trophic relationships and energy transfer to higher trophic levels were estimated by using fatty acid trophic markers and by applying stable isotopes of carbon and nitrogen. The energy rich Calanus species are key links between primary producers and higher trophic levels in the Icelandic waters. The Calanus species dominate the zooplankton biomass around Iceland and their markers (20:1n9 and 22:1n11) are found in high amount in animals at higher trophic levels. Calanus finmarchicus plays important role as a forage species in the Atlantic water south-west of Iceland while its high importance is replaced by the larger lipid rich C. hyperboreus in the Arctic and sub-Arctic waters north of Iceland. Even though Calanus based food-web is the main driver in both areas, there exist a pathway where Calanus species are of less importance and the energy is channeled via euphausiids to higher trophic levels. This study presents novel important knowledge on the food web structures and carbon flow in Icelandic waters.