Impacts of food availability and pCO2 on planulation, juvenile survival, and calcification of the azooxanthellate scleractinian coral Balanophyllia elegans

[摘要] Ocean acidification, the assimilation of atmospheric CO₂ by the oceansthat decreases the pH and CaCO₃ saturation state (Ω) ofseawater, is projected to have severe adverse consequences for calcifyingorganisms. While strong evidence suggests calcification by tropicalreef-building corals containing algal symbionts (zooxanthellae) will declineover the next century, likely responses of azooxanthellate corals to oceanacidification are less well understood. Because azooxanthellate corals donot obtain photosynthetic energy from symbionts, they provide a system forstudying the direct effects of acidification on energy available forcalcification. The solitary azooxanthellate orange cup coral Balanophyllia elegans often lives inlow-pH, upwelled waters along the California coast. In an 8-month factorialexperiment, we measured the effects of three pCO₂ treatments (410, 770,and 1220 μatm) and two feeding frequencies (3-day and 21-day intervals)on "planulation" (larval release) by adult B. elegans, and on the survival, skeletalgrowth, and calcification of newly settled juveniles. Planulation rates wereaffected by food level but not pCO₂. Juvenile mortality was highestunder high pCO₂ (1220 μatm) and low food (21-day intervals).Feeding rate had a greater impact on calcification of B. elegans than pCO₂. Whilenet calcification was positive even at 1220 μatm (~3times current atmospheric pCO₂), overall calcification declined by~25–45%, and skeletal density declined by ~35–45% aspCO₂ increased from 410 to 1220 μatm. Aragonitecrystal morphology changed at high pCO₂, becoming significantly shorterbut not wider at 1220 μatm. We conclude that food abundance iscritical for azooxanthellate coral calcification, and that B. elegans may be partiallyprotected from adverse consequences of ocean acidification in habitats withabundant heterotrophic food.

[学科分类] 地球化学与岩石