Effect of increasing sea water pCO2 on the northern Atlantic krill species Nyctiphanes couchii

Surprisingly little is known about potential effects of ocean acidification on krill of the Northern Hemisphere as ecologically very important food web component. Sub-adult individuals of the northern Atlantic krill species Nyctiphanes couchii (caught at Austevoll near Bergen, Norway, in January 2013) were exposed in the laboratory to four different levels of pCO2 (430, 800, 1,100, and 1,700 µatm) for 5 weeks in order to assess potential changes in a set of biological response variables. Survival decreased and the frequency of moulting-related deaths increased with increasing pCO2. Survival was considerably reduced at relatively high pCO2 of 1,700 µatm and tended to be negatively affected at 1,100 µatm pCO2. However, the experimental results show no significant effects of pCO2 on inter-moult period and growth at pCO2 levels below 1,100 µatm. No differences in length measurements of the carapace and uropod were observed across pCO2 levels, indicating no effect of changing carbonate chemistry on the morphology of those calciferous parts of the exoskeleton. The results suggest that sub-adult N. couchii may not suffer dramatically from predicted near-future changes in pCO2. However, potential detrimental effects on the moulting process and associated higher mortality at 1,100 µatm pCO2 cannot be excluded. Further experiments are needed in order to investigate whether early life stages of N. couchii show a different sensitivity to elevated sea water pCO2 and whether those results are transferable to other krill species of the Northern Hemisphere.