Ocean acidification and the early life history of marine fish

If the current trajectory of greenhouse gas emissions is maintained, atmospheric CO2 concentrations will exceed 500ppm by mid-century and could reach between 730-1020ppm at the end of the century. The continued uptake of additional CO2 at the ocean surface would cause ocean pH to decline by 0.3-0.4 units compared to current-day levels, with a rate of change faster than at any time during the past 650,000 years. Here, I discuss laboratory and field-based experiments designed to test the effects of ocean acidification on the early life history of tropical reef fishes. Elevated CO2 and reduced pH did not have a negative affect on embryonic duration, size at hatching, survival, and growth of larvae and juveniles in several common reef species. Similarly, skeletal and otolith development of larvae and juveniles were not affected by exposure to water acidified with up to 1000ppm CO2. In contrast, dramatic changes were observed in the behaviour of larvae and newly-settled juveniles when exposed to seawater that had been treated with CO2-enriched air. Larval damselfish reared in control seawater discriminated between a range of cues that could help them locate suitable settlement habitat and avoid predators. This discriminatory ability was impaired in larvae reared in conditions simulating ocean acidification. Larvae exposed to elevated CO2 were more active and exhibited riskier behavior in natural coral-reef habitat. As a result, they had higher mortality from predation than current-day controls. These results indicate that larval growth and development might not be adversely affected by ocean acidification, but that the disruption of larval behaviour could have profound effects on population replenishment and connectivity patterns of many marine species.

Munday, P., 34th Annual Larval Fish Conference, conference abstracts, Web site.

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