Physiological responses to hypoxia and anoxia in Balanus amphitrite (Cirripedia: Thoracica)

The barnacle Balanus amphitrite Darwin is a dominant intertidal and major fouling organism. As its life cycle includes both sessile and pelagic phases, adaptation is a necessity to tolerate harsh conditions that are faced in the intertidal and pelagic environment. A downward trend in dissolved oxygen levels in coastal areas has been recently observed, which would have a more prominent effect on sessile organisms inhabiting the intertidal habitats. The effects of reduced dissolved oxygen levels (hypoxia) and no oxygen (anoxia) on B. amphitrite adults and nauplii was assessed. Their response was evaluated by estimating the levels of the antioxidant enzymes catalase and superoxide dismutase. The impact of desiccation on antioxidant enzymes in adult B. amphitrite collected from different tidal heights was also evaluated. When nauplii were starved, 100% mortality was observed after 64 h under hypoxia, and between 24 and 32 h under anoxia. However, when nauplii were exposed to hypoxia and anoxia along with food, their tolerance level increased. A decrease in naupliar feeding rate and oxygen consumption was observed when they were exposed to hypoxia and anoxia. A significant difference in the levels of antioxidant enzymes in adult B. amphitrite collected at different tidal levels was observed. Enzyme activity increased with increase in the duration of tidal exposure, suggesting a capability to adapt to stress in different niches. Nauplii showed antioxidant defense (increased enzyme activity) under hypoxia and anoxia. The magnitude of change in enzyme levels suggests that these enzymes could be potential biomarkers of stress.