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This work resulted from the DIAPOD project (NE/P0063513/1), part of the Changing Arctic Ocean programme, jointly funded by the UKRI Natural Environment Research Council (NERC) and the German Federal Ministry of Education and Research (BMBF).
Sampling strategy and experimental procedure
Ingestion and egg production rates of Calanus finmarchicus and C. glacialis females were measured during a series of 120-hour food-removal incubations, using the natural plankton assemblage as feeding substrate. Incubations were conducted across the Fram Strait in May-June 2018 and August 2019 aboard RRS James Clark Ross (cruises JR17005 and JR18007 respectively).
For each experiment, 10 copepods were added to each of six experimental bottles (2.2L), and three experimental bottles were incubated without female copepods to account for microplankton growth during the incubation. All experimental bottles were placed on a plankton wheel and left for 24 hours before refreshing the water.
At the start and end of each 120 hour period:
- Copepods were frozen at -80 oC for elemental and lipid analysis
At the start and end of each 24 hour period:
- The plankton assemblage was preserved using Lugol’s iodine
- The plankton assemblage was filtered to analyse the elemental, isotopic and lipid composition
- Eggs were collected and frozen at -80 oC for elemental and lipid analysis when numerous
Cells were identified and enumerated after settling through inverted microscopy. Cell volumes were calculated through measuring different dimensions and applying geometric formulae. Cell volumes were converted to carbon biomass using published conversion factors specific to the cell type3. Groupings were as follows:
- Small centric diatoms (radius <5 µm)
- Large centric diatoms (radius ≥5 µm)
- Pennate diatoms
Clearance and ingestion rates were calculated using the equations of Frost2. The carbon specific ingestion was estimated using the mean carbon content of the female Calanus spp. and the ingestion rate. An estimated carbon budget was created for the copepods4,5,6,7. This is still a work in progress and so has not been included in the poster.
- Lipid analysis of copepods, the plankton assemblage and the eggs
- Creating a balanced carbon budget
- Use of stoichiometric model to determine limiting nutrient
1- Hop, H., Falk-Petersen, S., Svendsen, H., Kwasniewski, S., Pavlov, V., Pavlova, O., and Søreide, J. E. (2006) Physical and biological characteristics of the pelagic system across Fram Strait to Kongsfjorden. Prog. Oceanogr., 71, 182–231.
2- Frost, B. W. (1972) Effect of size and concentration of food particles on the feeding behaviour of the marine planktonic copepod Calanus pacificus. Limnol. Oceanogr., 6, 805–815.
3- Menden-Deuer, S. and Lessard, E. J. (2000) Carbon to volume relatinship for dinoflagellates, diatoms and other protist plankton. Limnol. Oceanogr., 45, 569–579
4- Ikeda, T., Kanno, Y., Ozaki, K., and Shinada, A. (2001) Metabolic rates of epipelagic marine copepods as a function of body mass and temperature. Mar. Biol., 139, 587–596
5- Landry, M. R., Hassett, R. P., Fagerness, V., Downs, J., and Lorenzen, C. J. (1984) Effect of food acclimation on assimilation efficiency of Calanus pacificus. Limnol. Oceanogr., 29, 361–364.
6- Mayor, D. J., Anderson, T. R., Irigoien, X., and Harris, R. P. (2006) Feeding and reproduction of Calanus finmarchicus during non-bloom conditions in the Irminger Sea. J. Plankton Res., 28, 1167–1179.
7- Mayor, D. J., Cook, K. B., Thornton, B., Walsham, P., Witte, U. F. M., Zuur, A. F., and Anderson, T. R. (2011) Absorption efficiencies and basal turnover of C, N and fatty acids in a marine Calanoid copepod. Funct. Ecol., 25, 509–518
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