Antagonistic and Synergistic Effects of Ocean Acidification and Global Warming on Sharks

Jennifer C.A.  Pistevos(1), Ivan Nagelkerken(1), Tullio Rossi(1), Maxime Olmos(2), Sean Connell(1)

 

1 1Southern Seas Ecology Laboratories, School of Biological Sciences and The Environment Institute, The University of Adelaide, South Australia 5005, Australia

2 ENSAIA, 2 Avenue de la Forêt de Haye TSA 40602 54518 Vandoeuvre-les-Nancy, France

 

Background: Apex predators typically exert substantial top-down forcing on trophically structured food webs, but there is lack of understanding how this function might be altered due to global change. In particular, the combined effect of elevated temperature on metabolism and of elevated CO₂ on the behaviour of larger predators may not only affect their foraging behaviour, but also the communities in which their prey live.

Methods: We used a factorial design in both long-term laboratory and mesocosm studies to assess how warming and ocean acidification affect development, growth, swimming activity, feeding and hunting behaviour in a mesopredator shark.

Findings: Our results showed that the projected increases in ocean temperature and CO2 are likely to act synergistically on predators by not only increasing energetic demands, but also decreasing metabolic efficiency and reducing food intake. Additionally, although temperature increased motivational drive to locate prey, elevated CO₂ negated olfactory and visual behavioural responses that enable effective hunting. Fundamental to these effects was the negligible effect of CO2 in isolation, but its power to negate the positive effects of temperature when brought in conjunction.

Conclusions: The reduced potential to locate prey due to the interactive effects of ocean acidification and warming, in combination with increases in energetic demand, suggests that energetic trade-offs will be needed for sharks to sustain themselves at an individual and population level in a future ocean. Alteration in growth and feeding of predators has important implications for the health and functioning of ecosystems.