Stable nitrogen and carbon isotopes of plankton samples and selected copoepods around the Iberan Peninsula 2001-2004

The structure and variability of pelagic food webs along the north and northwestern shelf of the Iberian Peninsula were analysed using natural abundance of nitrogen stable isotopes of plankton and pelagic consumers. Plankton composition was mainly studied in size-fractionated samples, but also the isotopic signatures of three copepod species, as representative of primary consumers, were considered. Several fish species were included as planktivorous consumers, with special attention to sardine (Sardina pilchardus). Finally, top pelagic consumers were represented by the common dolphin (Delphinus delphis). The relationship between trophic position and body size implies large variability in the ratio of predator to prey sizes, likely because widespread omnivory and plankton consumption by relatively large predators. Planktivorous species share a common trophic position, suggesting potential competition for food, and low nitrogen isotope enrichment between prey and consumers suggest nutrient limitation and recycling at the base of the food web. Both experimental and field evidences indicate that the muscle of sardine integrates fish diet over seasonal periods and reflects the composition of plankton from large shelf areas. The low mobility of sardines during periods of low population size is consistent with differential isotopic signatures found in shelf zones characterised by upwelling nutrient inputs.

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.