According to the experiments, therefore, ocean acidification alone presumably cannot have much impact on copepods. Only recently did Barbara Niehoff’s colleagues discover something astonishing that reinforces this presumption. Copepods have a special talent: they can regulate the pH value in their bodily fluids.
AWI scientists observed that the pH value of some copepods was only around six during their winter dormancy. As a comparison: a pH value of six corresponds to the degree of acidity of human urine. Seawater, by contrast, is slightly alkaline with a pH value of eight. However, as soon as copepods woke up from winter dormancy and started to eat, their inner pH value went back up to eight.
Does this mean we can give the all-clear for copepods? Not entirely. Copepods primarily feed on unicellular algae and their community will probably change as a result of climate change. In future, therefore, the number of smaller algae could increase. Furthermore, if sea ice retreats earlier in spring, algae will also reproduce earlier in spring – that means at a time when the copepods are still dormant in the depths of the Arctic Ocean.
Barbara Niehoff’s next research questions are, therefore: What do copepods eat if their favourite food, diatoms, has nearly vanished already when the animals wake up from their winter dormancy? Can they also live on significantly smaller flagellates? Initial tests indicate to the biologist that Arctic copepods might reach their limits here. This is because if they have to ingest less or inferior food, the animals no longer grow optimally and their population could decline – possibly with severe consequences for the entire Arctic food web. Indirectly, therefore, acidification and warming might just have an impact on the otherwise so resistant copepods.