The effect of nutrition on important life-history traits in the marine copepod Calanus finmarchicus

Abstract

Summary of thesis: Copepods dominates the zooplankton biomass in all seas of the world and are probably the most numerous multicellular organism on earth. Calanus finmarchicus (Gunnerus 1770) is the dominating copepod species in the North Atlantic. C. finmarchicus builds up rich lipid reserves during spring to survive dormancy during winter, and spawn the subsequent spring. The annual production of C. finmarchicus in the Norwegian Sea is estimated to 29 million tonnes of carbon with a production to biomass (P/B) ratio of 4.3. In 2011, the first commercial fishery on C. finmarchicus opened in the Norwegian Sea and a new management plan for commercial harvest of C. finmarchicus is being developed. Sustainable fisheries of the C. finmarchicus stock rely on ecosystem models, and these models use input parameters on biological variables like reproductive rates, growth rates, mortality and feeding selectivity. In this thesis, the effect of nutrition on important life-history traits in Calanus finmarchicus was studied: reproduction, growth, lipid dynamics, and feeding selectivity. The egg production in C. finmarchicus was shown to depend on the food concentration, the nutritional quality of the food and the concentration of highly unsaturated fatty acids (HUFAs) in the females. The somatic growth in nauplii (juvenile) stages of C. finmarchicus showed no significant relationship with food concentration, but was positively correlated with the content of DHA and EPA in the food. Our study on the lipid dynamics of C. finmarchicus showed that the content of important HUFAs was related to the fatty acid composition in available food (microalgae). Population data from the same paper showed that the abundance of C. finmarchicus in the surface of the Trondheimsfjord varied greatly between years, although the overwintering population was similar, indicating that the fjord may not be a suitable harvesting area. Feeding selectivity was studied by creating a gradient of ciliates (microzooplankton) in the food offered to C. finmarchicus. Our results support studies that classify C. finmarchicus as an omnivorous species; ciliates are an important supplementary food source during spring bloom conditions and a major food source during post-bloom conditions