The effects of arsenic and seawater acidification on antioxidant and biomineralization responses in two closely related Crassostrea species

Ocean acidification processes are major threats to marine calcifying organisms, mostly affecting biomineralization related processes. Abiotic stressors acting on marine systems do not act alone, rather in a combination of multiple stressors, especially in coastal habitats such as estuaries, where anthropogenic and environmental pressures are high. Arsenic (As) is a widely distributed contaminant worldwide and its toxicity has been studied on a variety of organisms. However, the effect of low pH on the toxicity of As on marine organisms is unknown. Here, we studied the combined effects of ocean acidification and As exposure on two closely related oyster species (Crassostrea angulata and Crassostrea gigas), by use of a biochemical approach. Oxidative stress related parameters were studied along with the assessment of biomineralization enzymes activity after 28 days of exposure. Results showed that both species were sensitive to all tested conditions (low pH, As and pH + As), showing enhancement of antioxidant and biotransformation defenses and impairment of biomineralization processes. Glutathione S-transferases (GSTs) activity were significantly higher in oysters exposed to As, showing activation of detoxification mechanisms, and a lower GSTs activity was observed in low pH + As condition, indicating an impact on the oysters capacity to detoxify As in a low pH scenario. Carbonic anhydrase (CA) activity was significantly lower in all tested conditions, showing to be affected by both As and low pH, whereas the combined effect of low pH + As was not different from the effect of low pH alone. Multivariate analysis of biochemical data allowed for the comparison of both species performance, showing a clear distinction of response in both species. C. gigas presented overall higher enzymatic activity (GSTs; superoxide dismutase; catalase; CA and acid phosphatase) and higher cytosolic GSH content in As exposed oysters than C. angulata. Results obtained indicate a higher tolerance capacity of the Pacific oyster C. gigas towards the tested conditions. (C) 2015 Elsevier B.V. All rights reserved.