Gobies inhabiting natural CO2 seeps reveal acclimation strategies to long-term acidification

Changes in ocean chemistry resulting from increasing acidification have direct impacts on the physiology and behaviour of teleosts. Ocean acidification (OA) can also affect species behaviour, survival and fitness with repercussions at population, community and ecosystem levels. Volcanic CO2 seeps offer a unique opportunity to study in situ both the direct and indirect effects of OA on fish and investigate their potential for acclimation. Here, we used the natural CO2 seeps in Vulcano Island, Italy to study the effects of OA on the brain transcriptome of the anemone goby, a species with high population density in the CO2 seeps. When compared to fish from environments with ambient pCO2, gobies living in acidified waters showed differences in expression of transcripts involved in ion transport and pH homeostasis, cellular stress, and immune response indicating their capability to mitigate CO2 induced oxidative stress and maintain physiological pH. We also found evidence of potential adaptive mechanisms to restore the functioning of GABA, whose activity can be affected by exposure to elevated CO2 levels. There was also a conspicuous difference in expression of core circadian rhythm transcripts which could provide an adaptive advantage by increasing flexibility of physiological processes under acidified conditions. Additionally, an overall increase in metabolism in fish from the CO2 seep indicates the ability to meet increased energetic costs associated with living in an acidified environment. Our results show potential molecular processes of acclimation to elevated pCO2 in gobies enabling them to thrive in the acidified waters of Vulcano Island. ### Competing Interest Statement The authors have declared no competing interest.