Abstract
The frequency and severity of coral bleaching events have increased in recent years. Global warming and contamination are primarily responsible for triggering these responses in corals. Thus, the objective of this study was to evaluate the isolated and combined effects of elevated temperature and exposure to copper (Cu) on responses of the antioxidant defense system of coral Mussismilia harttii. In a marine mesocosm, fragments of the coral were exposed to three temperatures (25.0, 26.6, and 27.3°C) and three concentrations of Cu (2.9, 5.4, and 8.6 μg/L) for up to 12 days. Levels of reduced glutathione (GSH) and the activity of enzymes, such as superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), and glutamate cysteine ligase (GCL), were evaluated on the corals and symbionts. The short exposure to isolated and combined stressors caused a reduction in GSH levels and inhibition of the activity of antioxidant enzymes. After prolonged exposure, the combination of stressors continued to reduce GSH levels and SOD, CAT, and GCL activity in symbionts and GST activity in host corals. GCL activity was the parameter most affected by stressors, remaining inhibited after 12-days exposure. Interesting that long-term exposure to stressors stimulated antioxidant defense proteins in M. harttii, demonstrating a counteracting response that may beneficiate the oxidative state. These results, combined with other studies already published suggest that the antioxidant system should be further studied in order to understand the mechanisms of tolerance of South Atlantic reefs.
Highlights
Ocean warming is the main factor causing bleaching in coral reefs worldwide (Hoegh-Guldberg, 1999; McWilliams et al, 2005; Yuyama et al, 2012)
Due to the importance of such symbiosis, the bleaching is directly related to episodes of mass mortality on coral reefs, which contributes to the degradation of this important ecosystem (Glynn, 1993, 1996; Hoegh-Guldberg, 1999; Suggett and Smith, 2019)
We evaluated the levels of GSH and the activity of the antioxidant enzymes superoxide dismutase (SOD), CAT, glutathione S-transferase (GST), and glutamate cysteine ligase (GCL) in M. harttii exposed to different levels of thermal stress, Cu concentrations, and the combination of both
Summary
Ocean warming is the main factor causing bleaching in coral reefs worldwide (Hoegh-Guldberg, 1999; McWilliams et al, 2005; Yuyama et al, 2012). The antioxidant defense system (ADS) includes enzymatic and non-enzymatic molecules, which reduce the amount of ROS and maintain the balance of the cellular oxidative state (Monteiro et al, 2006; Suggett and Smith, 2019). Antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), and glutamate cysteine ligase (GCL), are responsible for acting in the neutralization of ROS. Due to the important role of these molecules in redox metabolism, they can be used as interesting parameters to assess an early warning response to coral bleaching in the face of multiple stressors (Weis, 2008; Higuchi et al, 2015)
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