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

Abstract

Ocean acidification (OA) refers to the ongoing decline in oceanic pH resulting from the uptake of atmospheric CO(2). 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 pCO(2) levels that represent average ambient conditions during coral spawning (∼400 μatm) and the range of pCO(2) increases that are expected to occur in this century [∼560 μatm (mid-CO(2)) and ∼800 μatm (high-CO(2))]. Fertilization, settlement, and growth were all negatively impacted by increasing pCO(2), 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 pCO(2) conditions projected for the middle and the end of this century, respectively. Additional declines of 39% (mid-CO(2)) and 50% (high-CO(2)) 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.

Fig. 1.

Results of fertilization, settlement, and growth experiments (mean ± 1 SEM). (A) A 26-d-old A. palmata juvenile reared under control conditions (ambient CO₂). (B) Nonlinear regressions of fertilization data by CO₂ treatment. Regressions were fit separately for each CO₂ concentration. Parameter estimates are outlined in Table 1. Data from the 0.32 × 10⁵ sperm mL⁻¹ · 673 μatm treatment were omitted from the regression due to the unavailability of reliable data for this cell as a result of sperm contamination (Materials and Methods and Fig. S2B). (C) Percent settlement of A. palmata by treatment (11 dAS). Model parameters are for actual settlement data (n = 24 wells); P values are from linear regression analysis of arcsine-transformed percentage data. (D) Linear extension (μm day⁻¹) of A. palmata juveniles by treatment over 50 d. Individuals exhibiting partial or full mortality were excluded from the analysis, resulting in fewer replicates in the mid- and high-CO₂ treatment groups (control, n = 11; mid-CO₂, n = 9; high-CO₂, n = 5).