Impacts of Warming, Acidification, and Deoxygenation on Embryos and Larvae of Gilthead Seabream (Sparus aurata).

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, undermining ocean services and uses. Nonetheless, no study has so far scrutinized the cumulative impact of these three stressors on fish embryos and larvae. To fill this knowledge gap, we conducted a fully multi-factorial experiment to investigate the effects of warming (+4 °C: 22 °C), acidification (Δ - 0.4 pH units: 7.7 pH, pCO2 ~1000 μatm), and deoxygenation (Δ - 60% O2 saturation: 3 mg O2 L-1) on physiological and behavioral responses of the commercially important species Sparus aurata. Deoxygenation was the primary factor reducing hatching rates (64.25%), survival (46.71%), and heart rates (31.99%) of recently hatched larvae, being generally further exacerbated when combined with warming and acidification. No larvae exposed to the interaction of the three treatments reacted to the phototactic behavior test. However, acidification alone caused a 50% reduction in phototactic behavior. Our findings demonstrate that the deadly trio is detrimental to early fish development, impacting several key features at this critical life stage, and the need to assess the impacts of stressors' interaction on marine taxa to better predict future ecosystem responses to ocean changes.