Abstract
Anthropogenic carbon dioxide (CO2) emissions and consequent ocean acidification (OA) are projected to have extensive consequences on marine calcifying organisms, including corals. While the effects of OA on coral calcification are well documented, the response of reproduction is still poorly understood since no information are reported for temperate corals. Here we investigate for the first time the influence of OA on sexual reproduction of the temperate azooxanthellate solitary scleractinian Leptopsammia pruvoti transplanted along a natural pCO2 gradient at a Mediterranean CO2 vent. After 3 months, future projection of pH levels did not influence the germ cell production, gametogenesis and embryogenesis in this azooxanthellate coral. These findings suggest that reproductive potential may be quite tolerant to decreasing pH, with implications for ecosystem function and services in a changing ocean.
Highlights
Anthropogenic CO2 absorbed by the ocean is decreasing seawater pH and changing ocean chemistry, reducing the availability of carbonate ions (CO32−)[1], the building blocks used by calcifying marine organisms, such as corals[2]
Specimens of L. pruvoti transplanted along the same pCO2 gradient as in the present study show a decrease in net calcification rates with decreasing pH, and a significant increase in polyp mortality rate, but only when average temperatures is high[38]
Increasing pCO2 showed no effects on the production of male and female germ cells, as suggested by the oocyte and spermary abundances, which were homogenous along the gradient in both periods analyzed, and by the presence of embryos in female corals during the fertilization period at all sites
Summary
Anthropogenic CO2 absorbed by the ocean is decreasing seawater pH and changing ocean chemistry, reducing the availability of carbonate ions (CO32−)[1], the building blocks used by calcifying marine organisms, such as corals[2]. The few available studies on the effects of ocean acidification on coral sexual reproduction were conducted in tropical species and only under laboratory conditions[19,21,22,23,24], lacking information on the complex natural environment[25]. Acidified areas (i.e. CO2 vents) mimic future ocean conditions and can be used as natural laboratories to investigate the effects of increasing pCO2 on marine ecosystems in situ[6,26,27,28,29]. This study investigated for the first time at the Panarea CO2 vents the effects of future pH scenarios on coral reproductive efficiency.
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