From the ‘Carbon Dioxide, is there anything it can’t destroy?’ department and the University of Adelaide’s department of science fiction, comes this laughable press release. Let’s see, sharks have been around for about 450 million years, and in that time the planet has been significantly warmer than today, and has had far higher CO2 levels than today during that time. Somehow, sharks managed to cope with that. And of course, this isn’t an in situ study of sharks hunting ability, noooo, it’s sharks in a tank with prey thrown in while these clowns jacked around with CO2 levels in the water. Studies in captivity are NOT the same as the ocean. Just ask any salt water aquarium owner how difficult it is to keep specimens healthy under even the best aquarium management practice. Even worse, they only studied one kind of shark, yet extrapolate that to all sharks in the headline of the press release. In my opinion, this study would get laughed out of any grade school science fair, but somehow it gets a pass in peer review.
Sharks’ hunting ability destroyed under climate change
The hunting ability and growth of sharks will be dramatically impacted by increased CO2 levels and warmer oceans expected by the end of the century, a University of Adelaide study has found.
Published today in the journal Scientific Reports, marine ecologists from the University of Adelaide’s Environment Institute report long-term experiments that show warmer waters and ocean acidification will have major detrimental effects on sharks’ ability to meet their energy demands, with the effects likely to cascade through entire ecosystems.
The laboratory experiments, studying Port Jackson sharks and including large tanks with natural habitat and prey, found embryonic development was faster under elevated temperatures. But the combination of warmer water and high CO2 increased the sharks’ energy requirement, reduced metabolic efficiency and removed their ability to locate food through olfaction (smelling). These effects led to marked reductions in growth rates of sharks.
“In warmer water, sharks are hungrier but with increased CO2 they won’t be able to find their food,” says study leader Associate Professor Ivan Nagelkerken, Australian Research Council (ARC) Future Fellow.
“With a reduced ability to hunt, sharks will no longer be able to exert the same top-down control over the marine food webs, which is essential for maintaining healthy ocean ecosystems.”
PhD student Jennifer Pistevos, who carried out the study, says the Port Jackson is a bottom-feeding shark that primarily relies on its ability to smell to find food. Under higher CO2, the sharks took a much longer time to find their food, or didn’t even bother trying, resulting in considerably smaller sharks.
Most research studying the effects of ocean acidification and climate change on fish behaviour has concentrated on small fish prey. Long-term studies on the behaviour and physiology of large, long-lived predators are largely lacking.
Fellow University of Adelaide marine ecologist Professor Sean Connell says the results of the study provide strong support for the call to prevent global overfishing of sharks.
“One-third of shark and ray species are already threatened worldwide because of overfishing,” Professor Connell says. “Climate change and ocean acidification are going to add another layer of stress and accelerate those extinction rates.”
UPDATE: As is typical of alarmist science that goes for headlines, they didn’t include a title for the paper, a DOI, or a link to the paper. I’ve dug it up and that information is below.
Ocean acidification and global warming impair shark hunting behaviour and growth
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.
The paper is open source here: http://www.nature.com/articles/srep16293
The Supplementary info is here: http://www.nature.com/article-assets/npg/srep/2015/151112/srep16293/extref/srep16293-s1.doc
Update 2: Based on table S2 of the SI, it seems they only tested for 400ppm and 1000ppm, no mention if they somehow increased that gradually [to mimic the natural rate of change over years]. The point is that at our current growth rate of CO2 in the atmosphere at ~2ppm it will take approximately 300 years for our atmosphere to reach that level. Just throwing sharks in a 1000ppm tank (even given a week) isn’t anywhere close to simulating that, and removes all natural evolutionary and adaptation processes from the experiment.
Update 3: I wonder how the media will reconcile the “destroyed” hunting ability of sharks with the claims that global warming caused shark attacks this past summer? Inquiring minds want to know.
Update4: David Hoffer writes in comments about what he found in the paper:
…you have to hunt through to finally find this snippet:
The eggs were left to acclimatize over a period of seven days where temperature was steadily increased by 1 °C to the elevated temperature treatment. The eggs were kept in either control (~400 μatm) or elevated CO2 (~1000 μatm)16,58 crossed with control (~16 °C) or elevated temperature (~19 °C)
They applied a change of +3 deg C over a period of days
The applied a change from 400 uatm CO2 to 1000 uatm CO2 over a period of days
Sure, let’s cram a century of change into one week and see what happens! It gets worse:
In addition, the whole experiment was only 68 days long. 68 days! They extrapolated results by weighing the sharks at 62 days and 68 days. Yes, a whole 6 days!
When they moved the sharks from the small hatching tanks to the larger environment, the elevated temp/co2 sharks were fed DOUBLE the control group for the first little while, and then their feeding was REDUCED for the later part of the experiment to match that of the control group. Why? And how would that affect the results at the end of the experiment?
I can’t even work up the energy to come up with an acerbic sarcastic remark.