Characteristics of eggs and female adults of Calanus finmarchicus, C. glacialis and C. hyperboreus from Disko Bay, western Greenland

This is the first high temporal-resolution study in Disko Bay covering population dynamics, grazing, reproduction, and biochemical composition of 3 dominating copepod species (Calanus finmarchicus, C. glacialis and C. hyperboreus) from late winter to midsummer in 2008. C. finmarchicus and C. glacialis ascended to the surface layer at the onset of the spring phytoplankton bloom, followed by C. hyperboreus 2 wk later. C. finmarchicus spawning occurred during the bloom and postbloom period, partially fueled by wax esters. C. glacialis commenced spawning before the bloom, yet it was greatly stimulated when food became available. However, feeding and reproduction was terminated after the main bloom despite the presence of food. In terms of feeding, this was also the strategy for C. hyperboreus. Between pre-bloom and post-bloom, C. finmarchicus showed an increase in carbon, nitrogen, and phospholipid content but a decrease in total lipid content. This was likely the result of protein synthesis, oocyte maturation, and spawning fueled by wax esters and by feeding. C. glacialis showed a similar pattern, although with an increasing total lipid content from pre-bloom to post-bloom, and an increasing wax ester and decreasing phospholipid content after reproduction was terminated. C. hyperboreus showed greatly increased content of carbon, nitrogen, and all lipid classes between the pre- and post-bloom periods. Hence, C. finmarchicus commenced feeding and spawning at the onset of the bloom and continued throughout the remaining study period. Both C. glacialis and C. hyperboreus females refueled their storage lipids (wax esters) during the bloom and post-bloom period, suggesting that they may spawn in an additional year.

In situ experiment on Calanus finmarchicus egg production and grazing rates using fecal pellet production as proxy. North Atlantic spring 2013

The pre-bloom grazing and egg production rates of Calanus finmarchicus were studied at in situ temperature and chlorophyll concentration during spring on North Atlantic cruise. The sampled transects covered the Iceland, Irminger and Labrador basins.

Diurnal egg and pellet production of Calanus finmarchicus collected during METEOR cruise M87/1 in Aril 2012

Egg and pellet production of Calanus finmarchicus was measured at 6-h intervals at all stations during the second leg of the cruise. Calanus was collected at the surface 150-m using a WP2 plankton net, and incubated in chl-max water for 24-h. Each 6 hours females were transferred to a new food solution and eggs and pellets were counted. In the end of the experiment, females were measured for prosome length. The purpose of the exercise was to calculate the minimum carbon consumption of Calanus, and how large proportion of ingestion is egested as fast sinking fecal pellets, and when.

Prosome length as well as carbon and nitrogen content of Calanus finmarchicus from the North Atlantic collected during Maria S. Merian cruise MSM26 in spring 2013

The prosome length of copepods from each station was measured on board with a dissecting microscope equipped with an ocular micrometer. Individuals were placed in pre-weighed tin caps and dried for 48 h at 60°C on board. Dry samples were transferred to the AWI and weighed again. Copepod dry mass was then calculated as the difference between the empty weight and the weight of the tin cap containing one individual. The content of carbon (C) and nitrogen (N) then was analysed with a CN-analyser (EuroEA Element Analyser, Hekatech) with acetanilide as standard.

Protein content of Calanus finmarchicus from the North Atlantic collected during Maria S. Merian cruise MSM26 in spring 2013

For the determination of water-soluble protein content of C. finmarchicus of the different stations the Qubit® Protein Assay Kit (Invitrogen) was used. Analysis was performed with extracts of 10 copepods. Working solution was prepared with Qubit® protein reagent and Qubit® protein buffer (1:200). 190 µL working solution was pipetted into each well of a micro plate and 10 µL of sample or Qubit® protein standard (0, 200 and 400 ng/µL) was added. Solutions were mixed and incubated for 15 min at room temperature. Measurements were conducted with a micro plate reader (TriStar LB 941, Berthold Technologies) at 485 nm excitation and 590 nm emission, using the software MikroWin2000 (Berthold Technologies).

Enzyme activities of digestive and metabolic enzymes of Calanus finmarchicus from Maria S. Merian cruise MSM26 in spring 2013

The present study aimed to contribute to the knowledge on the intraspecific variations of enzyme activities in populations of Calanus finmarchicus from different longitudes across the North Atlantic Ocean and their relation to changing environmental conditions. C. finmarchicus was sampled across the North Atlantic in basins with decreasing temperature regimes from east to west (Iceland Basin, Irminger Basin and Labrador Basin) in late March/early April 2013. Potential maximum enzyme activities of digestive (proteinases and lipases/esterases) and metabolic (citrate synthase) enzymes of copepods from all sampling stations were analysed and thermal profiles (5-50°C) of enzyme activities were determined. In order to investigate its acclimation potential, C. finmarchicus were acclimated to 4°C and 15°C for two weeks and thermal profiles of enzyme activities were compared afterwards.

Enzyme activities of Calanus finmarchicus from the North Atlantic collected during Maria S. Merian cruise MSM26 in spring 2013

The activities of proteinases, lipases/esterases and citrate synthase of Calanus finmarchicus copepodites (CV) were analysed. Analysis was performed at 30°C for copepods from seven stations (126-9, 127-17, 131-17, 133-6, 134-19, 135-16, 136-8). In addition, thermal profiles (5-50°C) of these enzymes were analysed for copepods from 3 stations (127-17, 133-6, 135-16). C. finmarchicus of station 127-19 have been acclimated on board to two different temperatures (4 and 15°C) for two weeks. Thermal profiles (5-60°C) of lipases/esterases and proteinases of adult females from each treatment were analysed. Groups of 10 individuals were used to prepare enzyme extracts for analysis. From each station/treatment, three groups were analysed, each of which was measured in triplicates. The activity of proteinases was determined photometrically after Saborowski et al. (2004, hdl:10013/epic.20836), modified after Kreibich et al. (2008, doi:10.1007/s10152-008-0112-0). Azocasein was used as substrate. The lypolytic activity of lipases and esterases in the extract was analysed fluorometrically after Knotz et al. (2006, doi:10.1016/j.cbpa.2006.07.019) using 4-methylumbelliferyl butyrate as substrate. Citrate synthase activity was analysed photometrically after Stitt (1984) modified by Saborowski and Buchholz (2002) with oxaloacetic acid as substrate. For detailed description please contact the author.

Grazing rates and body mass of Calanus finmarchicus and Calanus glacialis incubated under elevated pCO2

It is currently under debate whether organisms that regulate their acid-base status under environmental hypercapnia demand additional energy. This could impair animal fitness, but might be compensated for via increased ingestion rates when food is available. No data are yet available for dominant Calanus spp. from boreal and Arctic waters. To fill this gap, we incubated C. glacialis at 390, 1120 and 3000 µatm for 16 days with Thalassiosira weissflogii (diatom) as food source on-board RV Polarstern in Fram Strait in 2012. Every four days copepods were sub-sampled from all CO2 treatments and clearance and ingestion rates were determined. During the SOPRAN mesocosm experiment in Bergen, Norway, 2011, we weekly collected C. finmarchicus from mesocosms initially adjusted to 390 and 3000 µatm CO2 and measured grazing at low and high pCO2. In addition, copepods were deep frozen for body mass analyses. Elevated pCO2 did not directly affect grazing activities and body mass, suggesting that the copepods did not have additional energy demands for coping with acidification, neither during long-term exposure nor after immediate changes in pCO2. Shifts in seawater pH thus do not seem to challenge these copepod species.