Paper Reviewed
Sampaio, E., Lopes, A.R., Francisco, S., Paula, J.R., Pimentel, M., Maulvault, A.L., Repolho, T., Grilo, T.F., Pousão-Ferreira, P., Marques, A. and Rosa, R. 2018. Ocean acidification dampens physiological stress response to warming and contamination in a commercially-important fish (Argyrosomus regius). Science of the Total Environment 618: 388-398.

In providing the rationale for their study, Sampaio et al. (2018) write that despite what they perceive to be "the inevitability of marine organisms having to cope with simultaneous effects of ocean warming, acidification and persistent contamination (methylmercury), no studies have focused on how the interactive effects between these three stressors will challenge fish ecophysiology." Thus, the team of eleven scientists set out to be the first to do so.

To accomplish their objective, Sampaio et al. exposed juvenile meagre (Argyrosomus regius) -- an oceanodromous teleost fish inhabiting the eastern Atlantic with increasing economic value within fisheries and aquaculture activities -- to isolated and combined warming (+4°C), acidification (pCO2 of 1100 µatm) and mercury contamination, the latter of which was accomplished be feeding fish a low- or high-contaminated mercury diet, containing approximately 0.12 or 1.6 mg Hg kg^-1 wet weight, respectively, for a period of 30 days.

Results of the analysis were quite astonishing. According to Sampaio et al., all stresses were sub-lethal; no mortalities occurred in any of the experimental treatments. They also found, not surprisingly, that mercury concentration in the fish "was enhanced under warming conditions." However, what was a surprise, was their observation that "elevated CO2 decreased mercury accumulation and consistently elicited a dampening effect on warming and contamination-elicited oxidative stress and heat shock response." Consequently, they report that "co-occurring acidification decreased heavy metal accumulation and contributed to physiological homeostasis."

In commenting on these important findings, Sampaio et al. say "we found evidence that, when co-occurring with other stressors, ocean acidification can simultaneously diminish heavy metal (mercury specifically) accumulation and its toxic effects, as well as the physiological stress response elicited by both mercury and ocean warming." Furthermore, they add that "ultimately, not only may these dampening effects translate into diminished contaminant biomagnification within the trophic chain, but also contribute to balancing fish physiology and promote homeostasis."

What is more, these several findings have key implications from a consumer perspective. For, according to the authors, "the counteracting CO2 effect (hampering warming-stimulate mercury accumulation) was consistent in the muscle, the main tissue ingested by human population." And because "this is the most relevant tissue for commercialization, such results constitute an important finding in the seafood safety research area."

Indeed they do. The human health implications of consuming A. regius under a scenario of combined ocean acidification and warming are much greater than those under a scenario of warming alone.