A review of comprehensive effect of ocean acidification on marine fishes

Increasing anthropogenic atmospheric CO2 is not only increasing global temperature but also rapidly acidifying seawater through the formation of carbonic acid. This results in another serious ecological problem: a process known as 'ocean acidification'. If the current trajectory of global emissions is maintained, atmospheric CO2 concentrations will exceed 500 μL/ L by mid-century and could reach between 730 and 1020 μL/ L at the end of the century. This would cause ocean pH to decline by 0. 3-0. 4 units compared with current-day levels (8. 06), with a rate of change many times faster than at any time during the past 650000 years. Research of ocean acidification involves many fields, including chemistry, ecology, biogeochemistry, and so on. Ocean acidification is expected to influence marine ecosystems through its effects on marine calcifying organisms (which biomineralize calcium carbonate into hard parts such as shells and skeletons), such as shelled mollusks and coral reefs. Most papers on ocean acidification have been published in the past decade, and have highlighted effects on marine calcifiers from a range of marine ecosystems including deep-sea and tropical corals. There are still some problems that need to be resolved. These effects are not well understood at the community and ecosystem levels, especially for non-calcifying species such as marine fishes, although the consequences are likely to involve range shifts and population declines. A current focus in ocean acidification research is to understand the resilience that organisms possess to withstand such changes, and to extend these investigations beyond calcification, addressing impacts on other vulnerable physiological processes. In general, marine fishes appear to be relatively tolerant to mild increases in CO2 and decreases in pH; however, the research on ocean acidification effects has been very scarce. Although we know little about the impacts of ocean acidification on marine fish, it does not mean that ocean acidification will have little or no effect on them. In fact, there is increasing evidence from laboratory experiments that elevated levels of dissolved CO2 and reduced seawater pH can affect developmental, metabolic and behavioral processes of some marine species, including some non-calcifying species, with highly significant consequences for population replenishment and sustainability. In general, ocean acidification could affect marine fish at all ontogenetic stages and mostly physiological duration. Most benthic marine species have a planktonic larval phase that must transition to a benthic existence to join the adult population. This life-history transition is usually associated with high rates of mortality and can be a period of strong sensitivity to environmental factors. Thus, the highest sensitivity of marine fishes is in the early life history stages, during which serious adverse impacts on the whole wild fish populations can arise. This paper summarizes empirical evidence for the impacts of ocean acidification on marine fish, and we hope that special emphasis will be placed on this important area of research.