Paper Reviewed
Almén, A.-K., Brutemark, A., Jutfelt, F., Riebesell, U. and Engström-Öst, J. 2017. Ocean acidification causes no detectable effect on swimming activity and body size in a common copepod. Hydrobiologia 802: 235-243.

Ocean acidification (defined as a decline in oceanic pH caused by the dissolution of atmospheric CO2 into the surface waters of the world's oceans) has been projected to impact marine life in a number of different ways, including growth, survival, fertility, calcification and organism behavior. Although much research has been conducted to date on this topic, there still remains much to be learned. And in this regard, Almén et al. (2017) note in their recent study that information on the effects of ocean acidification on copepod behavior and activity is lacking. And, therefore, they set out to remedy this situation.

The objective of Almén et al.'s work was to investigate both the acute and long-term impacts of a 0.22 pH unit decline (corresponding to a pCO2 increase from 450 to 700 µatm) on Pseudocalanus acuspes, a marine pelagic crustacean that inhabits both the North Sea and the Baltic Sea. The specific behaviors analyzed pertained to the copepod's swimming activities, where the authors used digital cameras and software to quantify a given animal's total activity, number of stops, freeze duration, medium speed count, medium speed duration, burst speed counts and burst speed duration in real-time.

In the long-term experiment, such behaviors were analyzed for copepods that were grown/reared in mesocosms deployed in the Gullmar Fjord on the west coast of Sweden, half of which had CO2 added to reduce the pH to the targeted level (pH of ~7.7) and half of which contained normal seawater to serve as a control (normal pH of ~7.9). Following a two-month incubation period, copepods from both the normal and reduced pH seawater mesocosms were transferred to a controlled-environment laboratory, where after an acclimation period, they were subjected to the behavior analyses. For the acute exposure experiment, a portion of the specimens from the control mesocosms were placed in elevated pCO2 seawater at the laboratory, whereupon their behavioral responses were examined following a 20-hour incubation period. And what did these two experiments reveal?

According to Almén et al., "there was no significant effect of CO2 on [copepod behavior] in chronic high-CO2, nor significant effect after the 20-hour acute exposure." The authors also report that copepod prosome length (a measure of body size that they hypothesized might be reduced in the long-term elevated pCO2 treatment) was unaffected by ocean acidification. And as a result of these findings, the five researchers conclude that "P. acuspes [does] not show sensitivity to near-future pCO2 levels."