Abstract
Coral reefs are one of the most susceptible ecosystems to ocean acidification (OA) caused by increasing atmospheric carbon dioxide (CO2). OA is suspected to impact the calcification rate of corals as well as multiple early life stages including larval and settlement stages. Meanwhile, there is now a strong interest in evaluating if organisms have the potential for acclimatization or adaptation to OA. Here, by taking advantage of a naturally acidified site in Nikko Bay, Palau where corals are presumably exposed to high CO2 conditions for their entire life history, we tested if adult and the next-generation larvae of the brooder coral Pocillopora acuta originating from the high-CO2 site are more tolerant to high CO2 conditions compared to the individuals from a control site. Larvae released from adults collected from the high-CO2 site within the bay and a control site outside the bay were reciprocally cultivated under experimental control or high-CO2 seawater conditions to evaluate their physiology. Additionally, reciprocal transplantation of adult P. acuta corals were conducted between the high-CO2 and control sites in the field. The larvae originating from the control site showed lower Chlorophyll-a content and lipid percentages when reared under high-CO2 compared to control seawater conditions, while larvae originating from the high-CO2 site did not. Additionally, all 10 individuals of adult P. acuta from control site died when transplanted within the bay, while all P. acuta corals within the bay survived at both control and high-CO2 site. Furthermore, P. acuta within the bay showed higher calcification and net photosynthesis rates when exposed to the condition they originated from. These results are one of the first results that indicate the possibility that the long-living corals could enable to show local adaptation to different environmental conditions including high seawater pCO2.
Highlights
Coral reefs are highly susceptible to ocean acidification (OA) which is caused by increasing concentrations of atmospheric carbon dioxide (CO2; Hoegh-Guldberg et al, 2007)
After the larvae were reciprocally cultivated at control or high CO2 seawater for 5 days, photosynthesis rate of the larvae cultured at high-CO2 was significantly higher than control seawater regardless of the seawater conditions where they originated from [F(1,32) = 8.68, p = 0.005], with no interaction (Figure 1 and Table 3)
A similar trend was observed at Day 5, where zooxanthella densities in the larvae originating from high-CO2 adults were significantly higher compared to larvae from control adults, regardless of the seawater conditions they were cultured under [F(1,36) = 9.31, p = 0.004], with no interaction [F(1,36) = 1.86, p = 0.18, Figure 2 and Table 3]
Summary
Coral reefs are highly susceptible to ocean acidification (OA) which is caused by increasing concentrations of atmospheric carbon dioxide (CO2; Hoegh-Guldberg et al, 2007). Evolution experiments studying the processes of adaptation to high pCO2 using short generation organisms such as phytoplankton are available (Lohbeck et al, 2012), we still lack for understanding multigeneration effects of OA on long-living organisms such as corals (Torda et al, 2017) In this context, organisms living in naturally acidified sites such as on CO2 vents (Hall-Spencer et al, 2008; Fabricius et al, 2011; Inoue et al, 2013) and sheltered lagoon (Shamberger et al, 2014; Golbuu et al, 2016) can be an ideal model to test adaptation potential and trans-generation responses to high pCO2 (Calosi et al, 2013; Harvey et al, 2016; Welch and Munday, 2017)
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