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We recently published a paper that contribute to our understanding on how certain coral species show a greater resistance to ocean acidification compare to other. This study was conducted at two CO2 seep, namely the CO2 seep at Shikine Island and the one at Normamby Island in Papua New Guinea. CO2 seeps allows us to distinguish resistant and sensitive species to chronic high CO2 exposure. It then possible whicheco-physiological traits can explain this difference in sensitivity. Here we investigated differences in energetic production. Using a method I developped earlier (Agostini et al., 2013, 2016) to measure mitochondrial electron transport system activities (ETSA) which represent the potential for energy,ie energy production. We showed that species sensitive to ocean acidification, “losing species”, showed a greater biomass (as amount of host protein per surface area) for a similar ETSA per surface area. Taken together this translated in greater biomass specific ETSA for “winning species” resistant to ocean acidification. Moreover we showed by sampling the few specimens of losing species found in the elevated CO2 area and through transplantation experiment, that this trait (high biomass specific ETSA) could not be acquired by losing species.

This study was also the first collaboration with the team of Riccardo Rodolfo-Metalpa and Fanny Houlbreque from the IRD in New Caledonia, and the continuation of the collaboration with Marco Milazzo. A memorable time spent off the shore of Papua New Guinea.

PNG Shikine

Contrasting seascapes at the Normanby Island and Shikine ISland CO2 seeps reference and elevated Co2 areas.

Citation

Agostini, S., Houlbreque, F., Biscéré, T., Harvey, B.P., Heitzman, J.M., Takimoto, R., Yamazaki, W., Milazzo, M., Rodolfo Metalpa, R., 2020. Greater mitochondrial energy production provides resistance to ocean acidification in ‘winning’ hermatypic corals. Front. Mar. Sci. 7. https://doi.org/10.3389/fmars.2020.600836

Abstract

Coral communities around the world are projected to be negatively affected by ocean acidification. Not all coral species will respond in the same manner to rising CO2 levels. Evidence from naturally acidified areas such as CO2 seeps have shown that although a few species are resistant to elevated CO2, most lack sufficient resistance resulting in their decline. This has led to the simple grouping of coral species into ‘winners’ and ‘losers’, but the physiological traits supporting this ecological assessment are yet to be fully understood. Here using CO2 seeps, in two biogeographically distinct regions, we investigated whether physiological traits related to energy production (mitochondrial electron transport systems activities) and biomass (protein contents) differed between winning and losing species in order to identify possible physiological traits of resistance to ocean acidification and whether they can be acquired during short-term transplantations. We show that winning species had a lower biomass (protein contents per coral surface area) resulting in a higher potential for energy production (biomass specific ETSA: ETSA per protein contents) compared to losing species. We hypothesize that winning species inherently allocate more energy towards inorganic growth (calcification) compared to somatic (tissue) growth. In contrast, we found that losing species that show a higher biomass under reference pCO2 experienced a loss in biomass and variable response in area-specific ETSA that did not translate on an increase in biomass-specific ETSA following either short-term (four to five months) or even life-long acclimation to elevated pCO2 conditions. Our results suggest that resistance to ocean acidification in corals may not be acquired within a single generation or through the selection of physiologically resistant individuals. This reinforces current evidences suggesting that ocean acidification will reshape coral communities around the world, selecting species that have an inherent resistance to elevated pCO2.

Reference

  1. Agostini, S., Fujimura, H., Fujita, K., Suzuki, Y., Nakano, Y., 2013. Respiratory electron transport system activity in symbiotic corals and its link to calcification. Aquatic Biology 18, 125–139. https://doi.org/10.3354/ab00496
  2. Agostini, S., Fujimura, H., Hayashi, H., Fujita, K., 2016. Mitochondrial electron transport activity and metabolism of experimentally bleached hermatypic corals. Journal of Experimental Marine Biology and Ecology 475, 100–107. https://doi.org/10.1016/j.jembe.2015.11.012