Abstract
Increases in atmospheric carbon dioxide (pCO2) are projected to contribute to a 1.1–6.4°C rise in global average surface temperatures and a 0.14–0.35 reduction in the average pH of the global surface ocean by 2100. If realized, these changes are expected to have negative consequences for reef-building corals including increased frequency and severity of coral bleaching and reduced rates of calcification and reef accretion. Much less is known regarding the independent and combined effects of temperature and pCO2 on critical early life history processes such as fertilization. Here we show that increases in temperature (+3°C) and pCO2 (+400 µatm) projected for this century negatively impact fertilization success of a common Indo-Pacific coral species, Acropora tenuis. While maximum fertilization did not differ among treatments, the sperm concentration required to obtain 50% of maximum fertilization increased 6- to 8- fold with the addition of a single factor (temperature or CO2) and nearly 50- fold when both factors interact. Our results indicate that near-future changes in temperature and pCO2 narrow the range of sperm concentrations that are capable of yielding high fertilization success in A. tenuis. Increased sperm limitation, in conjunction with adult population decline, may have severe consequences for coral reproductive success. Impaired sexual reproduction will further challenge corals by inhibiting population recovery and adaptation potential.
Highlights
Atmospheric carbon dioxide has increased from approximately 280 ppm to 390 ppm since the start of the industrial revolution due to anthropogenic activities such as the burning of fossil fuels, cement production, and land use changes [1]
The most likely consequences of ocean acidification and warming, respectively, are generally regarded as reduced calcification/reef accretion [2] and increased frequency and severity of coral bleaching [3]. These concerns, in combination with recent trends in reef degradation caused by local stressors, have led to predicted future scenarios that range from spatially heterogenous declines dominated by shifts in community composition [4], [5] to global-scale loss of coral reefs [6], [7]
Maximum fertilization (Fertmax) did not differ among treatments (F3,148 = 0.502, P = 0.681), but the fertilization curve shifted horizontally such that the sperm concentration required to achieve half of the maximum fertilization (EC50) increased with the addition of experimental factors (F3,148 = 141.7, P,0.0001) (Fig. 2b; Table 3)
Summary
Atmospheric carbon dioxide (pCO2) has increased from approximately 280 ppm to 390 ppm since the start of the industrial revolution due to anthropogenic activities such as the burning of fossil fuels, cement production, and land use changes [1]. The most likely consequences of ocean acidification and warming, respectively, are generally regarded as reduced calcification/reef accretion [2] and increased frequency and severity of coral bleaching (a breakdown of the symbiotic relationship between corals and their endosymbiotic algae) [3] These concerns, in combination with recent trends in reef degradation caused by local stressors (e.g., overexploitation and pollution), have led to predicted future scenarios that range from spatially heterogenous declines dominated by shifts in community composition [4], [5] to global-scale loss of coral reefs [6], [7]. In light of the recent trends in reef loss, there is an urgent need to understand how global warming and ocean acidification will affect the reproductive capacity, and the recovery potential, of reef-building corals
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