Ocean acidification (OA) threatens the existence of coral reefs by slowing the rate of
calcium carbonate (CaCO3) production of framework-building corals thus reducing the amount of
CaCO3 the reef can produce to counteract natural dissolution. Some evidence exists to suggest that
elevated levels of dissolved inorganic nutrients can reduce the impact of OA on coral calcification.
Here, we investigated the potential for enhanced energetic status of juvenile corals, achieved via
heterotrophic feeding, to modulate the negative impact of OA on calcification. Larvae of the
common Atlantic golf ball coral, Favia fragum, were collected and reared for 3 weeks under
ambient (421 ?atm) or significantly elevated (1,311 ?atm) CO2 conditions. The metamorphosed,
zooxanthellate spat were either fed brine shrimp (i.e., received nutrition from photosynthesis plus
heterotrophy) or not fed (i.e., primarily autotrophic). Regardless of CO2 condition, the skeletons of
fed corals exhibited accelerated development of septal cycles and were larger than those of unfed
corals. At each CO2 level, fed corals accreted more CaCO3 than unfed corals, and fed corals reared
under 1,311 ?atm CO2 accreted as much CaCO3 as unfed corals reared under ambient CO2.
However, feeding did not alter the sensitivity of calcification to increased CO2; ?calcification/??
was comparable for fed and unfed corals. Our results suggest that calcification rates of
nutritionally replete juvenile corals will decline as OA intensifies over the course of this century.
Critically, however, such corals could maintain higher rates of skeletal growth and CaCO3
production under OA than those in nutritionally limited environments.