Swimming activity and body size of Pseudocalanus acuspes (KOSMOS 2013, Kristineberg, Sweden)

Ocean acidification can impair an animal's physiological performance and energetically demand- ing activities such as swimming. Behavioural abnor- malities and changed activity in response to ocean acidification are reported in fish and crustacean species. We studied swimming activity in the calanoid copepod Pseudocalanus acuspes in response to near- future ocean acidification. Water and copepods were sampled from ten mesocosms deployed on the Swedish west coast. The experiments were conducted on animals reared in the mesocosms for 2 months during spring. Copepods were filmed after long-term (chronic) high-CO2, and after 20 h acute exposure to CO2. There was no significant effect of CO2 on copepods in chronic high-CO2, nor significant effect after the 20 h acute exposure. In addition, we measured prosome length from a large number of adult copepods, but no effect of acidification on body size was found. In this study, P. acuspes did not show sensitivity to near-future pCO2 levels. Even if a number of papers suggest that copepods seem robust to future ocean acidification, interaction between multiple stress factors, such as elevated temperature, hypoxia and salinity changes may impair a copepod's ability to resist lowered pH.