Ocean acidification compromises recruitment success of the threatened Caribbean coral Acropora palmata

Ocean acidification (OA) refers to the ongoing decline in oceanic pH resulting from the uptake of atmospheric CO₂. Mounting experimental evidence suggests that OA will have negative consequences for a variety of marine organisms. Whereas the effect of OA on the calcification of adult reef corals is increasingly well documented, effects on early life history stages are largely unknown. Coral recruitment, which necessitates successful fertilization, larval settlement, and postsettlement growth and survivorship, is critical to the persistence and resilience of coral reefs. To determine whether OA threatens successful sexual recruitment of reef-building corals, we tested fertilization, settlement, and postsettlement growth of Acropora palmata at pCO₂ levels that represent average ambient conditions during coral spawning (∼400 μatm) and the range of pCO₂ increases that are expected to occur in this century [∼560 μatm (mid-CO₂) and ∼800 μatm (high-CO₂)]. Fertilization, settlement, and growth were all negatively impacted by increasing pCO₂, and impairment of fertilization was exacerbated at lower sperm concentrations. The cumulative impact of OA on fertilization and settlement success is an estimated 52% and 73% reduction in the number of larval settlers on the reef under pCO₂ conditions projected for the middle and the end of this century, respectively. Additional declines of 39% (mid-CO₂) and 50% (high-CO₂) were observed in postsettlement linear extension rates relative to controls. These results suggest that OA has the potential to impact multiple, sequential early life history stages, thereby severely compromising sexual recruitment and the ability of coral reefs to recover from disturbance.