Impact of hypoxia, warming and acidification on the early ontogeny of tropical sharks

Chair: Elvira Poloczanska

Rui Rosa (1)*, Ana Couto (1), Maria Rita Pegado (1), Catarina Santos (1), Marta Pimentel (1), Tiago Repolho (1) and José R. Paula (1)

1 MARE – Marine and Environmental Sciences Centre, Laboratório Marítimo da Guia, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal

Background
Sharks occupy high trophic levels in marine habitats and play a key role in the structure and function of marine communities. Their populations have been declining worldwide by ≥90% and their adaptive potential to future ocean conditions is believed to be limiting.

Methods
Here we investigated the combined effects of overnight hypoxia (2 mg l-1 O2; usual in coral flats at night), ocean warming (+4 °C; 30 °C) and acidification (ΔpH=0.5) on survival, metabolic and ventilation rates, food intake, lateralization and other behavioural traits, and respiratory, neuronal and antioxidant enzymatic machinery of recently-hatched bamboo shark (Chiloscyllium punctatum).

Findings
Thirty days post hatching, juvenile sharks revealed a significant decrease in survival, metabolism, food intake and brain aerobic potential (citrate synthase activity) under hypoxic-warm-acidified conditions. Besides loss of lateralization, neonates revealed a more lethargic behaviour. An array of antioxidant enzymes (glutathione S-Transferase, superoxide dismutase activity and catalase) acted in concert to detoxify ROS, but this significant up-regulation was not enough to minimize the drastic increase in brain’s peroxidative damage and cholinergic neurotransmission.

Conclusions
We argue that the future conditions may elicit deleterious deficiencies in sharks’ critical biological processes which, at the long-term, may have detrimental cascading effects at population and ecosystem levels.