Coral reefs acclimatized to elevated carbon dioxide concentrations at natural Co2 seeps in Papua New Guinea

The study is based on field investigations of clear-water coral reefs and seagrass communities around three cool volcanic seeps of ~99% CO2 gas, and at three adjacent control sites with similar geomorphology, seawater temperature and salinity, that fringe the D'Entrecastraux Islands, Milne Bay Province, Papua New Guinea.Co2 has been streaming from the seabed for over 70 years (likely much longer), resulting in localised acidified conditions: seeps (pCO2 ,500 to 900 ppm, pHTotal 7.8 – 7.9) adjacent control areas (pCO2 ,390 ppm,pHTotal ,8.0 – 8.05)Field surveys were conducted from 2010 to characterise seawater chemistry and ecological and physiological conditions in coral reefs control sites and seeps. See Fabricius et al. (2011) for further details.Environmental parameters (measured: pH, dissolved inorganic carbon, total alkalinity, salinity, and temperature; calculated with CO2SYS software: pCO2 and aragonite saturation state) were obtained across a 4-year period (2010–2013) at 1–5 m depth in both control and seep sites.A total of 433 colonies were sampled from six species of scleractinian coral: Acropora millepora, Pocillopora damicornis, Seriatopora hystrix, Poritescylindrica, massive Porites sp. and Galaxea fascicularis. Favites pentagona was the only species that occurred in moderate abundance at the extreme seep site and 10 colonies were sampled from the Upa-Upasina seep.DNA sequencing and statistical analysis was conducted, see Noonan et al. (2013)Samples of A. millepora, G. fasciularis, P.damicornis, and massive Porites. Analysis were analyised for skeletal porosity, bulk density and micro-density as described in the paper Prada et.al (2021), led by the team at the University of Bologna, Italy.