A research team has revealed the basis to variability across different fish species and uncovered that some species evolve more rapidly, providing them with evolved molecular toolkits and allowing them able to cope with future ocean acidification.

Global ocean surface pH is projected to decline with the ongoing uptake of anthropogenic atmospheric CO₂ by the oceans, a process termed ocean acidification (OA). A decade of laboratory experiments indicate that predicted OA conditions affect some marine fishes’ physiological performance, growth, survival, and crucial behaviours for the survival of the fish.

To test how marine life will respond and whether adaptation to this rapid acidification is possible, researchers went to a remote place on this planet to study in situ exposure to elevated partial pressure of carbon dioxide (pCO₂, the amount of carbon dioxide dissolved in water) and be able to predict how in the wild fish can cope with these environmental conditions predicted to exist across the globe by the end of this century. With rapidly changing environments due to human activities, it is crucial to be able to predict what will happen to marine organisms and in particular fish populations to optimise our conservation and management efforts.

The study here indicated some fish species that evolve more rapidly may have a flexible way to cope with OA, which should be helpful for these species to maintain their population size and biodiversity. However, for some other species evolving slowly, OA will be difficult for them once the OA level is beyond their tolerance levels.

Natural laboratories with elevated pCO₂

Volcanic CO₂ seeps can be used as natural laboratories where CO2 rises from the substratum and acidifies the surrounding seawater to levels similar to, or sometimes beyond, the projections for ocean acidification by the end of this century. Six adult coral reef fish species including damselfishes and a cardinalfish species from a reef within the Upa-Upasina CO₂ seep in Papua New Guinea (pH 7.77, pCO₂ 846 µatm) and an adjacent reef (500 m distance) with ambient pCO₂ (pH 8.01, pCO₂ 443 µatm) were sampled, tissues were extracted, analysed and sequenced for their cellular response to elevated CO₂ in their brains. The six fish species in this study are common coral reef fish but exhibit slightly different ecologies including differences in parental care and being active during the day or night, and therefore we can, to a certain extent, extrapolate the found patterns also to other fishes.

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