| Summary: | Oceanic uptake of anthropogenic CO2 is causing substantial changes in ocean chemistry: reducing pH, increasing surface temperature and reducing dissolved oxygen. Using natural CO2 vents to study the effects on marine organisms enables better projections of future ecosystems than laboratory studies can achieve. This study outlines a preliminary investigation into the suitability of natural CO2 vents near White Island, Bay of Plenty, New Zealand (37°30.583’S, 177°10.767’E) for climate change research. Water chemistry and vent gas samples were collected from two vent and three control locations to assess the influence of White Island’s vents on the surrounding environment. Two separate vent sites are located off White Island (37°31.013'S, 177°11.647'E; 37°31.005’S, 177°11.713’E). The most active site reduced mean pH to 7.49 (SD=0.40, n=3) and increased temperatures 0.4°C above background levels during winter and the moderate outgassing site reduced mean pH to 7.85 (SD=0.23, n=3) and increased temperatures 0.2°C above background in summer. Methane release from vent gases ranged from 0.5-0.8%, similar to the range found at other CO2 vent sites. There were no significant differences in trace and major metals between CO2 vent and control locations around White Island, but open ocean water samples showed significantly lower concentrations of sulfur, calcium and potassium when compared to sites closer to the Island. Increased metal concentrations at White Island sample sites may have resulted from recent volcanic activity and requires investigation over a longer time. The low pH and increased temperatures in seawater from White Island’s vents make this a potential location for studying the multi-stressor effects of projected climate changes in a natural environment with acclimated organisms and ecosystem-scale studies. The effects of CO2 vents on the CaCO3 skeletons of an abundant sea urchin, Evechinus chloroticus, and crustose coralline algae were also examined. Specimens from vent and non-vent sites were collected to test for variation in skeletal carbonate mineralogy. Mg-calcite skeletons of urchin E. chloroticus showed a range of wt.% MgCO3 between 4.5-4.9 in primary spines and 9.3-10.0 in test plates, neither of which varied significantly between vent and control sites. Mean Mg/Ca ratio was 0.06 for primary spines and 0.12 for test plates; the less soluble low Mg-calcite spines may be a potential adaptation to protect urchin spines against dissolution in their more exposed outer body. Skeletons of Mg-calcite crustose coralline algae (probably incorporating a variety of species) also did not show significant differences in wt.% MgCO3 (range=12.0-12.9). Coralline algae showed a potential adaptation to acidic conditions as specimens from one control site had increases in less soluble aragonite which indicates these important encrusters have the potential to shift either skeletal mineralogy or species present in response to climate change. Qualitative comparisons of calcite skeletons under SEM saw greater deformation and dissolution in coralline algae calcite crystals from vent sites compared to controls. These studies, along with the observed conditions at White Island, suggest that it has considerable potential as a “natural laboratory” for the study of multi-stressor climate change impacts in New Zealand.
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