The effects of the “deadly trio” (warming, acidification, and deoxygenation) on fish early ontogeny

Abstract

Abstract The interaction between increased dissolved carbon dioxide, rising temperatures, and oxygen loss – the so-called “deadly trio” – is expected to strongly affect marine biota over the coming years, potentially undermining ocean services and uses. Nonetheless, no study has so far scrutinized the cumulative impact of these three stressors on fish embryonic and larval stages, known to be particularly vulnerable to environmental stress. To fill this knowledge gap, we implemented a fully multi-factorial design to investigate the effects of acute warming (Δ + 4°C; 22 ºC), acidification (Δ − 0.4 pH units; ~ 7.7 pCO2) and deoxygenation (Δ − 60% O2 saturation, ~ 3 mg O2 l− 1) over a comprehensive array of physiological (hatching success, survival rates, deformities rates, and heart rates) and behavioural responses (larvae responsiveness and phototaxis) across the early ontogeny of the temperate gilthead seabream (Sparus aurata). Deoxygenation was the main driver of negative impacts in the hatching success (64.25%), survival (46.71%), and heart rates (31.99%) of recently hatched larvae, being generally further exacerbated when warming and acidification co-occurred. On the other hand, acidification was the only factor to induce a significant decrease in the proportion of phototactic behaviour (50%). The behavioural and physiological responses showed to be highly correlated across experimental treatments, specifically, phototaxis was negatively correlated with the incidence of malformations, and positively correlated with heart rates. Overall, our findings indicate that the interaction between warming, acidification, and deoxygenation is markedly detrimental to fish early developmental stages, impacting several key features at this critical life stage that may eventually cause adverse carry-over effects. Importantly, our analysis highlights the need to assess the concurrent impacts of stressors’ interaction on marine taxa to better predict future ecosystem responses to ocean changes.