Oral Presentation Australian Society of Fish Biology and Oceania Chondrichthyan Society Conference 2016

Future ocean conditions and the development, physiology, and behaviour of shallow sharks (#116)

Jodie Rummer 1 , Connor Gervias 1 2 , Dennis D.U. Heinrich 2 3 , Martijn S. Johnson 2 , Daniel W Kraver 2 , Tiffany J. Nay 2 , Gillian M.C. Renshaw 4
  1. James Cook University, Townsville, QLD, Australia
  2. ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Queensland, Australia
  3. Southern Shark Ecology Group, School of Biological Sciences, Faculty of Science & Engineering, Flinders University, Bedford Park, South Australia, Australia
  4. Hypoxia and Ischemia Research Unit, School of Allied Health Science, Griffith University, Gold Coast, Queensland, Australia

Increasing atmospheric CO2 (43% since the Industrial Revolution) is warming the oceans (2.0-4.8°C by 2100), increasing the frequency and extent of hypoxia (low oxygen), and decreasing ocean pH (0.3-0.4 units by 2100; ocean acidification) at a rate 100-times faster than over the past million years. Tropical sharks may be some of the most negatively affected by climate change. Warmer, narrow temperature ranges and their life history – slow growing, late sexual maturity, and low reproductive output – could mean they are unable to adapt fast enough to keep pace with climate change. The epaulette shark (Hemiscyllium ocellatum) may be different. This species lives on shallow coral reef flats and in lagoons where they may frequently encounter short-term periods of challenging environmental conditions (e.g. hypoxia, elevated CO2, and temperature fluctuations) especially during low tides. Indeed, epaulette sharks are remarkably tolerant to short periods (hours) of hypoxia, and we have been recently investigating this species after prolonged exposure to elevated CO2 and temperatures – as would be relevant under climate change – in ovo, upon hatching, as neonates, and into adulthood. Overall, adults are both behaviourally and physiologically tolerant to elevated CO2, and our results from embryos reared under end-of-century CO2 conditions suggest that tolerance may start very early in life, just post-fertilization. Yet, we are only just beginning to understand the consequences of elevated temperatures and the importance of acclimation and movement to this species. Epaulette sharks may already possess adaptations that allow them to survive and thrive under the challenging environmental conditions they are already experiencing in their shallow reef habitats – adaptations that may also confer tolerance to conditions projected for the oceans by the end of this century. Projects are underway to determine whether other elasmobranchs, especially pelagic species that may not experience such fluctuations in their environment, will be equally as tolerant.