Guest essay by Eric Worrall
A study, pH homeostasis during coral calcification in a free ocean CO2 enrichment (FOCE) experiment, Heron Island reef flat, Great Barrier Reef led by researcher Lucy Georgiou has concluded that at least some Coral has the ability to regulate its own internal PH. This allows the studied coral to thrive, even in extreme acid environments.
From the conclusion of the study;
Importantly, individual nubbins exhibited near constant δ11B compositions along their major growth axis over each of the four growth periods measured, regardless of whether they were grown under treatment or control conditions (Fig. 2A and Fig. S4A). These near constant δ11B compositions equate to near constant internal pHcf (Fig. 2B and Fig. S4B), irre- spective of treatment and season and declined by less than 0.1 units per unit decrease in external pHsw (Δp Hcf =Δp Hsw= 0.067, P = 0.078, df = 36; Table S2 and Fig. 2B). This result reflects the ca- pacity of these coral to homeostatically maintain a pHcf of ∼8.4–8.6 at the site of calcification (Fig. 3) and thus near constant up-regu- lation of pHcf during the calcification process. As such, these findings are in marked contrast to earlier laboratory studies in which corals grown under stable and constant pH conditions exhibited a stronger sensitivity to ambient seawater pH, whereby pHcf decreased by up to 0.5 units for each unit decrease in ambient seawater pH. However, under the naturally and highly dynamic pH conditions within the Heron Island reef flat, corals seemingly exert a much stronger physiological control of pH, which overrides the seasonal ambient depression in seawater pH, as well as the super- imposed FOCE induced decrease in seawater pH. Reinterpretation (11) of previous laboratory work using P. cylindrica colonies under depressed pCO2 conditions (29) indicates that pH up-regulation was taking place at the site of calcification in this species; these previous experiments, however, kept CO2 constant throughout the experiment and therefore did not capture the dynamic nature of many natural reef environments.
Regardless, the ability of pH-homeostatic coral to survive and grow in these extreme pH environments may provide them with a greater resilience to the increased levels of ocean acidification expected to occur over the coming decades and centuries.
Lucy Georgiou led an intensive study into the resilience of coral to changes in CO2 level, which challenges many of the populist assumptions about coral and CO2. Her team also re-analysed the studies of other researchers, and worked out and stated why they think other researchers got it wrong. All this while working under the auspices of the University of West Australia, Lewandowsky’s old campus.