Acidification of Polluted Estuaries: Is It Bad News for Shell Fish?
Ivanina, A.V. and Sokolova, I.M. 2013. Interactive effects of pH and metals on mitochondrial functions of intertidal bivalves Crassostrea virginica and Mercenaria mercenaria. Aquatic Toxicology 144-145: 303-309.
Continuing, the two U.S. researchers say "survival in these environments requires efficient mechanisms of stress tolerance and involves a variety of cellular and physiological mechanisms of stress protection," as has been described by Hochachka and Somero (2002), Menge et al. (2002) and Somero (2002). And they add, in this regard, "metabolic regulation plays a key role among those mechanisms allowing intertidal animals to maintain a positive energy balance and survive prolonged periods of extreme stress," referencing Sokolova and Portner (2001), Altieri (2006), Gracey et al. (2008) and Sokolova (2013).
In further exploring this intriguing subject, Ivanina and Sokolova examined the interactive effects of seawater pH and the presence of a pair of toxic trace metals - cadmium (Cd) and copper (Cu) at levels of 25 µM of each separately - on the mitochondrial functions of two common marine bivalves: hard clams (Mercenaria mercenaria) and eastern oysters (Crassostrea virginica).
The two scientists say their study showed "mitochondrial functions of the intertidal bivalves C. virginica and M. mercenaria are relatively insensitive to pH in a broad physiologically relevant range." But when they were impacted at more extreme values, they found ocean acidification "modulates the response of their mitochondria," such that a decrease in pH was actually proven protective of the clams and oysters.
Ivanina and Sokolova conclude "moderate acidosis (such as occurs during exposure to air, extreme salinities or elevated CO2 levels in the intertidal zone) may have a beneficial side-effect of protecting mitochondria against toxicity of metals," in that "reduced intracellular pH caused by exposure to elevated CO2 levels abolished the metal-induced generation of reactive oxygen species in isolated clam cells (Ivanina et al., 2013) consistent with a mitochondrial mechanism of the cytoprotective effects of moderate acidification," while noting that a similar mechanism had been "experimentally demonstrated for the surface proteins of unicellular algae" in the studies of Niyogi and Wood (2004), Wilde et al. (2006) and Esbaugh et al. (2013).
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