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The Impact of Ocean Acidification on Juvenile Fish Digestion

Paper Reviewed
Jacob, H., Pouil, S., Lecchini, D., Oberhänsli, F., Swarzenski, P. and Metian, M. 2017. Trophic transfer of essential elements in the clownfish Amphiprion ocellaris in the context of ocean acidification. PLoS ONE 12: e0174344.

Writing as background for their study, Jacob et al. (2017) say that "little information exists on the effects of ocean acidification (OA) on the digestive and post-digestive processes in marine fish." Therefore, it was the aim of these six scientists to investigate this important topic. In doing so, Jacob et al. exposed juvenile clownfish (Amphiprion ocellaris) to normal (pH = 8.0) and reduced (pH = 7.5) seawater pH and fed them radiolabeled-food, which allowed them to monitor the absorption kinetics of essential elements (including Co, Mn and Zn) to determine the assimilation efficiencies of those elements.

Results of the analysis revealed there were "no statistically significant differences in the assimilation efficiency of juvenile clownfish exposed to high-level treatments of pCO2 when compared to [that of] the fish in the control treatment." Jacob et al. also report that the stomach pH of the clownfish during digestion was not affected by OA either, suggesting that "OA impacts do not affect element assimilation in these fish," while adding that "this apparent pCO2 tolerance may imply that clownfish have the ability to self-regulate pH shifts in their digestive tract, or that they can metabolically accommodate such shifts."

The results of Jacob et al.'s analysis are important in that they counter initial prevailing wisdom on the subject. Previously, researchers found that OA led to substantial decreases in digestive enzymes (Frommel et al., 2011; 2014; Pimentel et al., 2015; Rosa et al., 2016), which finding has been interpreted as an indicator that OA interferes with fish digestion. The new work of Jacob et al., however, demonstrates that although "OA can reduce the enzyme activity of juvenile fish, it may thus not ultimately result in a decrease in assimilation (integrative process). Indeed, some metabolic functions can be affected by a variation of seawater pH (or pCO2) but, according to the present study, the ultimate process (viz. trophic transfer of essential element) may not." And that is one reason why it is important not to jump to conclusions about the future impacts of OA on marine life -- a suspected problem may well turn out to be a non-problem!

Frommel, A.Y., Maneja, R., Lowe, D., Malzahn, A.M., Geffen, A.J., Folkvord, A., Piatkowski, U., Reusch, T.B.H. and Clemmesen, C. 2011. Severe tissue damage in Atlantic cod larvae under increasing ocean acidification. Nature Climate Change 2: 42-46.

Frommel, A.Y., Maneja, R., Lowe, D., Pascoe, C.K., Geffen, A.J., Folkvord, A., Piatkowski, U. and Clemmesen, C. 2014. Organ damage in Atlantic herring larvae as a result of ocean acidification. Ecological Applications 24: 1131-1143.

Pimentel, M.S., Faleiro, F., Diniz, M., Machado, J., Pousão-Ferreira, P., Peck, M.A., Pörtner, H.O. and Rosa, R. 2015. Oxidative stress and digestive enzyme activity of flatfish larvae in a changing ocean. PLoS ONE 10: 1-18.

Rosa, R., Pimentel, M., Galan, J.G., Baptista, M., Lopes, V.M., Couto, A., Guerreiro, M., Sampaio, E., Castro, J., Santos, C., Calado, R. and Repolho, T. 2016. Deficit in digestive capabilities of bamboo shark early stages under climate change. Marine Biology 163: 60.

Posted 25 August 2017