An in situ reciprocal transplant experiment was carried around a volcanic CO2 vent (Vulcano Island, Aeolian Archipelago, Italy) to evaluate the anti-predator responses of an anemone goby species exposed to ambient (∼380 μatm) and high (∼850 μatm) CO2 sites during two sampling surveys on May 17th – June the 2nd 2019, and 9–18 September 2019. Behavioral observations followed a well-established protocol adopted previously for other fish species, which consisted in recording gobies responses before and after the presentation of a predator (i.e. predator stimulus). Specifically, for each replicate a 4-min pre-stimulus presentation period was followed by a 4-min post-stimulus presentation period during which each fish was exposed to the visual and olfactory cues of an adult painted comber S. scriba. During the pre- and the post-stimulus periods we measured: the activity level, as the amount of time (sec) spent by the fish swimming in the entire experimental compartment; (ii) the time spent (sec) by the fish actively swimming or resting at 20 cm from the predator compartment (no predator zone); (iii) the shelter use, as the total time the fish spent near the anemone (i.e. less than 5 cm); (iv) the minimum approach distance, as the mean smallest distance (cm) of the fish centroid from the shelter (A. viridis).

Support was provided by the Japan Society for the Promotion of Science (日本学術振興会) as core-to-core funding (Advanced Research Network, https://www.jsps.go.jp/english/e-c2c/adopted_a.html) for 2021-2026.