Knowledge Bank

Coral reefs are among the most ecologically diverse and economically important habitats on earth, yet the combined effects of ocean acidification and warming threaten the integrity of these ecosystems globally. The reefs surrounding Oahu, Hawaii provide an exceptional opportunity to survey physiological variation among coral species that are found across a naturally occurring range of pCO2 and temperature conditions representative of the current average values for tropical reefs globally, through those expected by midcentury under climate-change. We hypothesize that populations of coral can adapt to high temperature and pCO2 conditions by adjusting aspects of their physiology that confer resilience. By comparing biomass and chlorophyll a from several species of coral distributed across these gradients, we seek to better understand the effects of higher temperature and pCO2 on coral physiology. In addition, some of the sites have high flow compared to others, presenting the opportunity to investigate how flow might mediate physiological responses to the temperature and pCO2. Findings from this work could shed light on the capacity of coral to acclimate or adapt to a future ocean that is both warmer and more acidic. Coral fragments were collected from sites around the island of Oahu, HI and flash frozen for transit to the Grottoli lab, where destructive analyses were performed to determine the concentration of Chl a and total biomass per sample. In the two branching coral species Montipora capitata and Porites compressa, biomass was lower and Chl a higher at sites with higher temp and pCO2 compared to sites with temperature and pCO2 more similar to today’s conditions. No such pattern was observed in the mounding species Porites lobata, suggesting that morphology influences resilience. Additionally, high flow appeared to minimize the negative effects of elevated pCO2/temp on biomass in the branching species M. capitata. These preliminary results suggest that adaptive responses to elevated pCO2 and temperature in Hawaiian coral are species-specific and that high flow sites might offer some refuge to corals in the future. Further scheduled analyses will provide a more comprehensive assessment of physiological variation across these gradients.