| Summary: | Increased atmospheric CO 2 emissions are inducing changes in seawater carbon chemistry, lowering its pH, decreasing carbonate ion availability and reducing calcium carbonate saturation state. This phenomenon, known as ocean acidification, is happening at a faster rate in cold regions, i.e., polar and sub-polar waters. The larval development of Arbacia dufresnei from a sub-Antarctic population was studied at high (8.0), medium (7.7) and low (7.4) pH waters. The results show that the offspring from sub-Antarctic populations of A . dufresnei are susceptible to a development delay at low pH, with no significant increase in abnormal forms. Larvae were isometric between pH treatments. Even at calcium carbonate (CaCO 3 ) saturation states (of both calcite and aragonite, used as proxies of the magnesium calcite) <1, skeleton deposition occurred. Polar and sub-polar sea urchin larvae can show a certain degree of resilience to acidification, also emphasizing A . dufresnei potential to poleward migrate and further colonize southern regions.
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