| Summary: | In light of future scenarios for the progressive decline in sea-water pH as a result of the accumulation of anthropogenic CO2 in surface waters, the present study investigates a shallow seep-site in the Tyrrhenian Sea that is venting 98% CO2 at ambient temperatures. Investigations addressed the effects of long-term exposure to elevated CO2 levels on the inter-tidal calcifying species, Patella caerulea, found on the littoral zone within 15-300 m of the vent site. Surface water pH reached 6.0 units adjacent to the vent zone, with PCO2 concentrations of 15,000 ftatm. The vents produced approximately 1.0 x 10* l ' CO2/ day. Two pH zones matching scenarios for predicted changes to surface ocean pH with 'no abated emissions' within the next 100 years (7.5-7.9) and levels expected as a result of leaks from deep-sea CO2 storage facilities (6.5-7.1) were determined. Signs of shell dissolution and weakening were evident in both of these zones. Detrimental effects to P. caerulea abundance and population structure were found where pH ranged from 6.5-7.1 units. The results obtained by this study strongly indicate that a reduction in sea-water to a pH from 6.5-7.1 pH units will be fatal for P. caerulea populations in the natural environment. Further, reductions in pH likely to be experienced by the end of this century may be harmful to shelled molluscs. Faculty of Science
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