Increased atmospheric CO2 levels will have a major impact on marine life, in particular on corals and molluscs, through the effects of ocean acidification on calcification. A recent international collaboration by researchers from Australia, Canada and the USA suggests that non-calcifying species, such as fishes, may also be adversely affected, as increased acidity has subtle but important effects.
The researchers, led by Philip Munday of James Cook University in Australia, studied the consequences of increased levels of acidity on the behaviour of larval clownfish – the striking white and orange fish that featured in the film Finding Nemo. Clownfish live near the bottom of the sea, but their larvae (which are a dull brown) drift as plankton. As they mature, the young clownfish need to find the adult population and avoid predators. Both these behaviours rely on chemical cues, which may be susceptible to changes in pH.
Munday and his co-workers reared clownfish larvae at normal sea-water pH (8.15), and also at increasing levels of acidity, induced by higher levels of CO2. They then used a simple flume chamber, in which the fish can choose to position itself in one of two parallel water sources, to test the ability of larvae to respond to various chemical stimuli. Current CO2 levels are around 390 p.p.m. or 0.039%; in 1960 the figure was around 360 p.p.m. (an 8% increase in 40 years). When reared under 390 p.p.m. CO2, all ages of larvae were able to avoid predator cues; similar responses were seen in larvae reared under a slightly higher CO2 level (550 p.p.m.).
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Cobb, M., 2010. Acid seas block Nemo’s nose. Journal of Experimental Biology 213, iii. Full article.
