Anti-predator responses of the Mediterranean anemone goby, Gobius incognitus, acutely and chronically exposed to ambient (∼380 μatm) and high (∼850 μatm) CO2 sites off a volcanic CO2 vent in Vulcano island, Italy

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 (i.e. the predator zone) and 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).