| Summary: | Anthropogenic atmospheric CO₂ levels are rapidly increasing; however, much of this CO₂ (ca. 30%) dissolves into the surface ocean (upper 200 m) where it reacts with seawater and disrupts both ocean pH and carbonate chemistry, a process termed ocean acidification. Average pH of the surface ocean has already decreased by 0.1 units since the beginning of the Industrial Revolution and is expected to drop another 0.2 to 0.4 units by the end of this century. Of primary concern is the potential for ocean acidification to dramatically disrupt biological processes, especially biogenic calcification. Different life history stages may also be affected in different ways. Furthermore, interactions between ocean acidification and other environmental perturbations are often non-additive and thus result in non-predictive outcomes. Here, I investigate the effects of ocean acidification on different life history stages of an endangered abalone, Haliotis kamtschatkana. I reared larvae and adults under elevated CO₂ conditions (800 and 1800 ppm), representing levels expected by the end of this century and beyond. Adults were also reared under two temperatures (9 and 12°C) to investigate interactions between CO₂ and temperature. Larval survival, shell size and shell morphology were negatively affected by elevated CO₂. At 1800 ppm, almost all larvae completely lacked a shell. Adults seem more tolerant of elevated CO₂. Survival, growth and feeding rates were unaffected by elevated CO₂, at either temperature. Early life history stages may be more sensitive due to differences in calcification processes. Near future levels of ocean acidification may dramatically impair early development of H. kamtschatkana but later life history stages may be more tolerant. Since H. kamtschatkana population growth is thought to be currently limited by successful fertilization, decreases in larval survival may have severe consequences for the recovery of this endangered species. Efforts to mitigate the dramatic population decline of H. kamtschatkana will need to consider the potential repercussions of ocean acidification.
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