The increase in anthropogenic carbon dioxide (CO₂) in the atmosphere is leading to higher ocean temperature and lower pH. At the same time, mercury released into the environment is also a fact, being deposited in the ocean. Thus, marine animals are being challenged by ocean warming, acidification and contamination simultaneously. However, their biological and physiological responses to these environmental changes still remain unknown. This study evaluated meagre (Argyrosomus regius) responses to the effects of ocean warming (+4ºC), acidification (ΔpH = 0.5 units) and MeHg exposure (8.02 mg kg⁻¹ dw), on Fulton condition index, degree of encephalization, acetylcholinesterase (AChE) levels, heat shock response (HSR), lipid peroxidation [malondialdehyde (MDA) concentration] and antioxidant enzyme activities [glutathione S-transferase (GST), catalase and superoxide dismutase (SOD)]. Temperature was the factor leading to an increase of MeHg accumulation in meagre. Survival and Fulton condition were not affected by any of the factors. Encephalizaton coefficient was only affected under the warming and hypercapnia non-contaminated treatment and only brain stem increased in response to warming. Moreover, AChE was only influenced under contaminated treatments. HSR only varied in muscle tissue and was mostly affected by warming treatments (non-contaminated and contaminated). In contrast, MDA levels were not influenced by warming, hypercapnia or contamination. GST increased under the warming non-contaminated treatment. Catalase was higher in samples from the contaminated hypercapnia treatment compared to the corresponding non-contaminated treatment, whereas SOD reached higher levels under the hypercapnia contaminated treatment. The present study shows that meagre will not suffer major consequences under predicted future ocean contaminated conditions. Although meagre suffered physiological alterations under these conditions, these responses were not harmful for the fish. These results suggest that meagre will be able to adapt to the predicted future ocean conditions even under mercury contamination. However, future studies will be necessary to comprehensively understand how marine biota will respond to the combined effects of future warming, acidification and pollution.
dos Reis Alves e Dias Francisco S., 2015. Combined effects of climate change and methylmercury exposure on the ecophysiology of juvenile meagre. MSc thesis, Universidade de Lisboa, 60 p. Thesis.
