Fish, bold on acid

If only fish could ‘just say no’. Acidification of seawater makes the most important fisheries species on the Great Barrier Reef in Australia live dangerously. Juvenile coral trout that experience higher than normal levels of acidity venture from shelter and become bold to the point they are attracted to the odour of potential predators, Professor Philip Munday of James Cook University, Queensland, and colleagues have found.

Results of the first comprehensive study of the effects of climate change on a commercially important tropical reef fish show that near-future ocean CO2 levels, of 700 and 960 microatmospheres, may compromise coral trout populations. “We found that the physiological mechanisms that fish use to control their blood and tissue pH, when exposed to higher CO2 levels, can interfere with the function of a major neurotransmitter receptor in the brain,” says Munday.

Fish can regulate ionic changes in blood to prevent acidosis, but this itself can alter the function of GABA-A neuroreceptors. Our colleague, Goran Nilsson from the University of Oslo, was the first person to discover the link between neuroreceptor function and all the abnormal behaviours we have reported. We predict that rising CO2 levels could cause sensory and behavioural impairment in a wide range of marine species, especially those that tightly control their acid–base balance through regulatory changes in bicarbonate and chlorine levels. Carbon dioxide levels used in the study are within the range of representative concentrat ion pathway trajectories adopted by the International Panel on Climate Change for 2100 and just beyond.

Interestingly, individuals varied in their response to predator odour at 700μ atm, which might indicate some potential for adaptation. However, it is not known if this variation has a genetic basis in coral trout, or if there is sufficient time for future generations to adapt to the rapid change in carbon dioxide levels. If adaptation cannot keep pace with the speed at which climate change occurs, long-term sustainability of wild harvests of coral trout will be undermined and aquaculture may prove critical to meet national and international demands. The United States National Oceanic and Atmospheric Administration says that by the end of this century, based on business as usual emission scenarios, the acidity of surface waters of the ocean could be 150 percent higher – a pH the oceans haven’t seen in over 20 million years.

If these predictions come to pass, is the future of fisheries in a glass bowl?

Hyne J., 2014. Fish, bold on acid. In Lasker H. W. (Ed.), Reef Encounter: The News Journal of the International Society for Reef Studies 29(1):23. Article.

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