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RESEARCH PRODUCT

Supplementary material - Details on study area, species, methods and additional results from Ocean acidification affects somatic and otolith growth relationship in fish: evidence from an in situ study

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Ocean acidification (OA) may have varied effects on fish eco-physiological responses. Most OA studies were carried out in laboratory conditions without considering the in situ pCO2/pH variability documented for many marine coastal ecosystems. Using a standard otolith ageing technique, we assessed how in situ ocean acidification (ambient, versus end-of-century CO2 levels) can affect can affect somatic and otolith growth, and their relationship in a coastal fish. Somatic and otolith growth rates of juveniles from a population of the ocellated wrasse Symphodus ocellatus living off a Mediterranean CO2 seep, increased at the high-pCO2 site. Also, we detected that slower growing individuals living at ambient pCO2 levels tend to have larger otoliths at the same somatic length (i.e. higher relative size of otoliths to fish body length) than faster growing conspecifics living under high pCO2 conditions, with this being attributable to the so-called ‘growth effect’. Our findings suggest the possibility of contrasting OA effects on fish fitness, with higher somatic growth rate and possibly higher survival associated to smaller relative size of otoliths that could impair fish auditory and vestibular sensitivity.