29The copepod Calanus finmarchicus is a key component of northern Atlantic food webs, linking 30 energy-transfer from phytoplankton to higher trophic levels. We examined the effect of different 53The carbonate concentration in seawater is declining due to increased pCO2 4 , and meta-analyses 54 indicate that calcifying organisms may be negatively affected by this phenomenon 5 . Marine 55 metazoans rely on a positive CO2 gradient from their body fluids to excrete metabolic CO2 by 56 diffusion. Elevated seawater pCO2 can therefore lead to hypercapnia and acidosis 6 which in turn 57 may result in a reallocation of resources away from growth and reproduction, due to mobilization 58 of energy demanding acid-base regulatory processes to counteract internal pH reduction. 59Accordingly, ocean acidification has been shown to negatively affect processes such as 60 reproduction 7 , development 8 and behavior 9 in non-calcifying organisms also. 61Copepods of the genus Calanus constitute a large part of the zooplankton biomass in the North 62 Atlantic 10, 11 . During the development from eggs, these copepods develop through six nauplii 63 stages (N1-N6), of which the two first (N1-2) are non-feeding, and five copepodite stages (C1-64 C5), before reaching maturity as either male or female 12 . These cold water species concentrate 65 and store energy through synthesis and accumulation of lipids and therefore represent an 66 important energy link between phytoplankton and higher trophic level predators such as fish 13, 14 67

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Mechanistic models are essential tools for interpreting and predicting the consequences of a changing environment and stressors such as pollution on the life histories of marine organisms. Here, we apply the simple and generic energy-budget model DEBkiss to the life history of the marine copepod Calanus finmarchicus. Model modifications were needed to accommodate the copepod life cycle, which deviates in several respects from most other animals (e.g., a sudden stop of growth after the final moult). We identified an acceleration of growth in the early copepodite stages, which could be linked to an increase in the specific feeding rate of the animals. Lipid storage, an essential element of C. finmarchicus biology, was successfully captured with the reproduction buffer of the DEBkiss model. The resulting model was fitted to a detailed data set from the literature and was able to explain growth, development and lipid storage from egg to adult, at different temperatures and food availabilities, within a single consistent framework. The parameterised model could subsequently be used to elucidate the energetic constraints on gonad maturation and reproduction. Interestingly, the overhead costs for egg production seem to be substantially higher than the default value applied in DEB-based studies. The current model provides a solid basis for applications in stress ecology, although our model analysis also identified several knowledge gaps. Specifically, further research is needed to cover the dynamics of diapause and gonad maturation, to explain the dependence of maximum body size on food and temperature, and to verify the predicted high costs for maturity maintenance.Electronic supplementary materialThe online version of this article (doi:10.1007/s00227-016-3030-8) contains supplementary material, which is available to authorised users.

The rates of ingestion of oil microdroplets and oil fouling were investigated in the zooplankton filter-feeder Calanus finmarchicus (Gunnerus, 1770) at 3 concentrations of oil dispersions ranging from 0.25 mg/L to 5.6 mg/L. To compare responses to mechanically and chemically dispersed oil, the copepods were exposed to comparable dispersions of micron-sized oil droplets made with and without the use of a chemical dispersant (similar oil droplet size range and oil concentrations) together with a constant supply of microalgae for a period of 4 d. The filtration rates as well as accumulation of oil droplets decreased with increasing exposure concentration. Thus the estimated total amount of oil associated with the copepod biomass for the 2 lowest exposures in the range 11 mL/kg to 17 mL/kg was significantly higher than the approximately 6 mL/kg found in the highest exposure. For the 2 lowest concentrations the filtration rates were significantly higher in the presence of chemical dispersant. Furthermore, a significant increase in the amount of accumulated oil in the presence of dispersant was observed in the low exposure group.

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