2.2 Behavioural analysis
After 7 days of current-day or elevated CO2 treatment, squid underwent sham treatment by being individually placed in 100 mL of aerated seawater from their CO2 treatment containing 0.2% ethanol for 30 minutes, as part of the experiment by Thomas et al. (2021). Visually-guided behaviour was then tested for 15 minutes by placing squid individually in a tank (30×30×15 cm) filled to 3 cm depth with seawater from their CO2 treatment and with a mirror taking up the entire area of one wall. Three aspects of squid behaviour shown to be altered by elevated CO2 in Thomas et al. (2021), activity level, aggressive conspecific-directed behaviour and exploratory conspecific-directed behaviour (Table 1), were used here. See Thomas et al. (2021) for a detailed description of the behavioural analysis and results.