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The Physiological Acclimation of the Common Clownfish to Global Warming

Paper Reviewed
Madeira, C., Madeira, D., Diniz, M.S., Cabral, H.N. and Vinagre, C. 2017. Comparing biomarker responses during thermal acclimation: A lethal vs non-lethal approach in a tropical reef clownfish. Comparative Biochemistry and Physiology, Part A 204: 104-112.

Model projections envision a world in which rising atmospheric CO2 concentrations raise future global sea surface temperatures 3 to 4 °C by the end of this century under a business-as-usual scenario. Such a temperature increase, if correct, is postulated to harm marine life, particularly those species living at or near levels of their assumed thermotolerances. And thus climate alarmists fret over potential global warming with projections of future species declines and possible extinctions in the years and decades ahead unless CO2 emissions are drastically reduced. New research, however, suggests the afore-mentioned concerns may well be vastly overstated, at least for a particular reef-dwelling fish.

The common clownfish (Amphiprion ocellaris) is a tropical reef fish popular in the aquarium trade. Given that it inhabits relatively warm waters presently, as well as its propensity to spend its entire life cycle attached to an anemone host, this species is considered to be particularly vulnerable to projections of future global warming. Or so it has been assumed. Working with a series of juveniles in a controlled laboratory experiment, Madeira et al. (2017) set out to examine the acclimation potential of A. ocellaris to rising temperature. This was done by exposing juvenile fish to seawater temperatures of either 26 or 30 °C for a period of four weeks, during which time they measured two biochemical markers -- one involved in preventing protein damage (heat shock protein 70, Hsp70) and another involved in dealing with it (ubiquitin, Ub) -- to determine the presence of thermal damage to cellular proteins. So what did they find?

In describing their findings, Madiera et al. say that there were no differences in survival rates among the control and elevated temperature treatments. However, they report that thermal stress was observed in the fish after one week of exposure (both biomarkers increased significantly), after which Ub levels decreased, which decrease the authors say suggests "the animals were able to acclimate." Thereafter, they continue, "as the juveniles acclimated to the new temperature conditions, Hsp70 kept showing increased levels in order to maintain cellular homeostasis, while the degree of irreversible damage (protein denaturation) started to decrease, as shown by lower Ub levels." Thus, Madiera et al. conclude that "A. ocellaris is capable of displaying a plastic response to elevated temperature by adjusting the protein quality control system to protect cell functions, without decreasing survival."

Commenting on their work, Madiera et al. say the observed physiological acclimation in A. ocellaris "may come as counterintuitive, considering that tropical species have evolved in a relatively stable thermal environment, and are therefore expected to exhibit narrower thermal reaction norms," yet acclimate they did, which finding indicates that this fish species (and likely many others with it) "do not seem to be in immediate danger due to direct effects of warming oceans." And that is exceedingly good news for this important reef-dwelling inhabitant.

Posted 27 September 2017