Ocean Acidification and Otolith Development in Clown Fish

According to Munday et al. (2011b), "in general, marine fish appear to be relatively tolerant to mild increases in ambient CO₂, presumably because well-developed mechanisms for acid-base regulation allow them to compensate for cellular acidosis caused by exposure to elevated pCO₂ (Portner et al., 2005; Ishimatsu et al., 2008; Melzner et al., 2009)." However, due to the fact that "fish otoliths (earbones) are composed of aragonite," they say there is a concern they "could be susceptible to the declining carbonate ion concentrations associated with ocean acidification," which could well be imagined to be quite serious, due to the fact that "fish ears detect sound, body orientation and acceleration from the position of the otoliths in the inner ear and movement of the otoliths over sensory hair cells (Helfman et al., 1997; Popper and Lu, 2000)."

In further exploring this intriguing subject, Munday et al. reared larvae of the marine clown fish Amphiprion percula throughout their entire larval phase at three different ocean acidification levels -- ambient or control conditions (CO₂ ~ 390 ppm, pH ~ 8.15) and higher CO₂/lower pH conditions (CO₂ ~ 1050 ppm, pH ~ 7.8; CO₂ ~ 1721 ppm, pH ~ 7.6) representative of conditions predicted to prevail in AD 2100 and AD 2200-2300, respectively -- in order to determine if the elevated CO₂/reduced pH conditions would alter otolith size, shape, symmetry (between left and right otoliths) or chemistry compared to current conditions.

The four researchers report that "there was no effect of the intermediate treatment on otolith size, shape, symmetry between left and right otoliths, or otolith elemental chemistry, compared with controls." In the more extreme treatment the story was much the same, except that otolith area and maximum length were slightly larger than controls, while "no other traits were significantly affected."

Munday et al. state that their data suggest that the larval clown fish is "capable of regulating endolymphic fluid chemistry even in waters with pH values significantly lower than open ocean values," and they thus conclude that "the larval clown fish is robust to levels of ocean chemistry change that may occur over the next 50-100 years," which conclusion is about the same as that reached by Munday et al. (2011a), who they say "detected no effects of ~850 ppm CO₂ on size, shape or symmetry of otoliths on juvenile spiny damselfish, a species without a larval phase."

Additional References
Helfman, G.S., Collette, B.B. and Facey, D.E. 1997. The Diversity of Fishes. Blackwell Science, Malden.

Ishimatsu, A., Hayashi, M. and Kikkawa, T. 2008. Fishes in high-CO₂, acidified oceans. Marine Ecology Progress Series 373: 295-302.

Melzner, F., Gutowska, M.A., Langenbuch, M., Dupont, S., Lucassen, M., Thorndyke, M.C., Bleich, M. and Portner, H.-O. 2009. Physiological basis for high CO₂ tolerance in marine ectothermic animals: pre-adaptation through lifestyle and ontogeny? Biogeosciences 6: 2313-2331.

Munday, P.L., Gagliano, M., Donelson, J.M., Dixson, D.L. and Thorrold, S.R. 2011a. Ocean acidification does not affect the early life history development of a tropical marine fish. Marine Ecology Progress Series 423: 211-221.

Popper, A.N. and Lu, Z. 2000. Structure-function relationships in fish otolith organs. Fisheries Research 46: 16-25.

Portner, H.O., Langenbuch, M. and Michaelidis, B. 2005. Synergistic effects of temperature extremes, hypoxia, and increases in CO₂ on marine animals: From earth history to global change. Journal of Geophysical Research 110: 10.1029/2004jc002561.