Brooded coral larvae differ in their response to high temperature and elevated pCO2 depending on the day of release.
To evaluate the effects of temperature and pCO2 on coral larvae, brooded larvae of Pocillopora damicornis from Nanwan Bay, Taiwan (21o56.179'N, 120o44.85'E), were exposed to ambient (419–470 matm) and high (604–742 matm) pCO2 at ~25 and ~29 oC in two experiments conducted in March 2010 and March 2012. Larvae were sampled from four consecutive lunar days (LD) synchronized with spawning following the new moon, incubated in treatments for 24 h, and measured for respiration, maximum photochemical efficiency of PSII (Fv/Fm), and mortality. The most striking outcome was a strong effect of time (i.e., LD) on larvae performance: respiration was affected by an LD x temperature interaction in 2010 and 2012, as well as an LD x pCO2 x temperature interaction in 2012; Fv/Fm was affected by LD in 2010 (but not 2012); and mortality was affected by an LD x pCO2 interaction in 2010, and an LD x temperature interaction in 2012. There were no main effects of pCO2 in 2010, but in 2012, high pCO2 depressed metabolic rate and reduced mortality. Therefore, differences in larval performance depended on day of release and resulted in varying susceptibility to future predicted environmental conditions. These results underscore the importance of considering larval brood variation across days when designing experiments. Subtle differences in experimental outcomes between years suggest that transgenerational plasticity in combination with unique histories of exposure to physical conditions can modulate the response of brooded coral larvae to climate change and ocean acidification.