Brain transcriptome of gobies inhabiting natural CO₂ seeps reveal acclimation strategies to long-term acidification

Ocean acidification (OA) is known to affect the physiology, survival, behaviour and fitness of various fish species with repercussions at the population, community and ecosystem levels. Some fish species, however, seem to acclimate rapidly to OA conditions and even thrive in acidified environments. The molecular mechanisms that enable species to successfully inhabit high CO₂ environments have not been fully elucidated especially in wild fish populations. Here, we used the natural CO₂ seep in Vulcano Island, Italy to study the effects of elevated CO₂ exposure on the brain transcriptome of the anemone goby, a species with high population density in the CO₂ seep and investigate their potential for acclimation. Compared to fish from environments with ambient CO₂, gobies living in the CO₂ seep showed differences in the expression of transcripts involved in ion transport and pH homeostasis, cellular stress, immune response, circadian rhythm and metabolism. We also found evidence of potential adaptive mechanisms to restore the functioning of GABAergic pathways, whose activity can be affected by exposure to elevated CO₂ levels. Our findings indicate that gobies living in the CO₂ seep may be capable of mitigating CO₂-induced oxidative stress and maintaining physiological pH while meeting the consequent increased energetic costs. The conspicuous difference in the expression of core circadian rhythm transcripts could provide an adaptive advantage by increasing the flexibility of physiological processes in elevated CO₂ conditions thereby facilitating acclimation. Our results show potential molecular processes of acclimation to elevated CO₂ in gobies enabling them to thrive in the acidified waters of Vulcano Island.