Ocean acidification and global warming impair shark hunting behaviour and growth.

Jennifer C A Pistevos,Ivan Nagelkerken,Maxime Olmos,Sean D Connell,Tullio Rossi

doi:10.1038/srep16293

Abstract

Alterations in predation pressure can have large effects on trophically-structured systems. Modification of predator behaviour via ocean warming has been assessed by laboratory experimentation and metabolic theory. However, the influence of ocean acidification with ocean warming remains largely unexplored for mesopredators, including experimental assessments that incorporate key components of the assemblages in which animals naturally live. We employ a combination of long-term laboratory and mesocosm experiments containing natural prey and habitat to assess how warming and acidification affect the development, growth, and hunting behaviour in sharks. Although embryonic development was faster due to temperature, elevated temperature and CO2 had detrimental effects on sharks by not only increasing energetic demands, but also by decreasing metabolic efficiency and reducing their ability to locate food through olfaction. The combination of these effects led to considerable reductions in growth rates of sharks held in natural mesocosms with elevated CO2, either alone or in combination with higher temperature. Our results suggest a more complex reality for predators, where ocean acidification reduces their ability to effectively hunt and exert strong top-down control over food webs.

Highlights

Global average sea surface temperatures are predicted to rapidly rise due to the greenhouse effect by 1°–3 °C in 2100 and this is in addition to an increase of ~0.76 °C in the last 150 years[16]
This study aims to determine: (i) the extent to which temperature and/or ocean acidification modify somatic growth through altered foraging rates, when food supply is unlimited, (ii) the effects of CO2 on hunting behaviour through olfaction, and (iii) the interactive effects of elevated temperature and CO2 on shark growth in mesocosms containing natural habitats and prey, where sharks need to hunt for their food
Elevated temperature increased the rate of embryonic development of sharks (Fig. 1, ANOVA; temperature, F 1,12 = 49.565; P = 0 .0001) but CO2 had neither an independent nor an interactive effect on hatch rates (Table S1) and 100% of the eggs hatched successfully with no mortality across any treatments

Summary

Introduction

Global average sea surface temperatures are predicted to rapidly rise due to the greenhouse effect by 1°–3 °C in 2100 and this is in addition to an increase of ~0.76 °C in the last 150 years[16]. Studies on the interactive effects of warming and ocean acidification on the performance of larger predators such as sharks are very limited[14], preventing us from better understanding their fate due to future change and how this might affect a change in the intensity of predation Another concern is that studies regularly use unrealistic elevations of temperature or CO2 and that most studies are done over short time periods and under simple laboratory conditions requiring cautious interpretation when applied to natural conditions. This study aims to determine: (i) the extent to which temperature and/or ocean acidification modify somatic growth through altered foraging rates, when food supply is unlimited, (ii) the effects of CO2 on hunting behaviour through olfaction, and (iii) the interactive effects of elevated temperature and CO2 on shark growth in mesocosms containing natural habitats and prey, where sharks need to hunt for their food. The direct effects of ocean warming on physiological performance was assessed in the laboratory, while in large mesocosms we studied the longer-term effects on shark performance by integrating metabolic effects and potential CO2 effects on hunting behaviour under more natural conditions

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Conclusion