Ontogenetic differences in the response of the cold-water coral Caryophyllia huinayensis to ocean acidification, warming and food availability

Cold-water corals (CWC) are exposed to multiple environmental stressors in a changing ocean. Several laboratory experiments have shown that adult CWC can survive at low pH and elevated temperature, but the effects on early life stages are largely unknown, let alone the interactive effects of changing pH, temperature and food availability. We conducted a six-month aquarium experiment to investigate the physiological responses of early juveniles, late juveniles and adults of the CWC Caryophyllia huinayensis to multiple environmental stressors by measuring key coral traits (survival, growth and respiration). We examined the single and interactive effects of pH (7.5 and 8.0), temperature (11 and 15 °C) and food availability (low and high) on the three life stages. The treatment levels reflect current conditions in the natural habitat of C. huinayensis in Comau Fjord, Chile. All life stages of C. huinayensis were more affected by warming than by acidification. At elevated temperature and in the combined treatment of elevated temperature and reduced pH, growth rates of all three life stages decreased after three months. After six months, mortality was highest in early juveniles and adults in these treatments. High feeding did not compensate for the negative effect of elevated temperature on growth and respiration rates of all life stages, but increased the growth rates of early and late juveniles at ambient and low pH conditions compared to low feeding. We identified ontogenetic shifts in resilience to future environmental conditions and highlight the importance of increased food availability for CWC resistance to ocean acidification. Our findings underscore the need to consider potential ontogenetic differences when addressing CWC responses to climate change