IRCP
Pacific Coral Reef Institute
EPHE

2014 IRCP grant awarding Jodie Rummer tells us about her research with sharks

Jodie and blacktip reef shark at CRIOBE« Globally, increased greenhouse gases due to agricultural and industrial development and the growing world population are resulting in a rapid increase in atmospheric CO2 at a rate 100 times faster than has ever been recorded in history. The oceans are absorbing approximately 30% of the atmospheric CO2, and the resulting reduction in ocean pH is predicted to be by as much as 0.3-0.4 units by the year 2100. Information necessary to understand how ocean acidification will affect marine life, especially tropical species that are predicted to be some of the most affected due to warmer temperatures, is lacking. Some studies suggest that, while elevated CO2 may not negatively affect physiological performance of some species, behaviours related to predator detection and decision-making may be impaired.  Understanding the impact of elevated CO2 on higher order predators, like elasmobranchs (sharks, skates, and rays), and interactions between ocean acidification and predator-prey dynamics will be pivotal to the continued health of coral reef and tropical ecosystems.

shark release, Moorea / L. Thiault

labwork at CRIOBE, Moorea

labwork at CRIOBE, Moorea

I investigated the physiological and behavioural effects of acute and prolonged exposure to elevated CO2 – levels chosen to simulate what is projected for the year 2100 (~1000µatm) – on juvenile blacktip reef sharks (Carcharhinus melanopterus).  Newly pupped sharks were collected via gillnet from Moorea lagoons and mangroves and held in flow-through aquaria at CRIOBE throughout the duration of the study, under either control or elevated CO2 conditions.  After 3 days and after 30 days I compared maximum and resting metabolic rates, recovery from exercise, and resting blood parameters between control and elevated CO2 exposed sharks. In addition, throughout the entire duration of the study, I also compared swimming behaviours, group interactions, and responses to food odors between groups. Given that these sharks utilize shallow lagoon and mangrove habitats as soon as they are born and during the first several months of their lives, it may be crucial for them to tolerate variations in water quality in order to exploit such areas for protection from predators and food sources. If more energy is required and/or activity is impaired under these experimental conditions, it could suggest that predator-prey and food web dynamics will be dramatically disrupted with climate change.

Data analyses are underway; however, it is already clear that the combination of ecology and physiology in this study is making for meaningful conclusions important to conservation issues regarding the effects of climate change on long-living, slow-to-reproduce tropical shark species that are key to healthy ecosystems. »

Jodie L. Rummer, Ph.D.

Australian Research Council (ARC) Discovery Fellow (early career)
ARC Centre of Excellence for Coral Reef Studies
James Cook University, Australia

 

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