Sharks just can’t seem to catch a break. Not only are they fished out of the ocean in the tens of millions per year and vilified as human-killing monsters, but it seems that they’re also set to be heavily impacted by the changing climate. A new study examines how an increase in ocean temperatures and acidification will affect the aquatic animals, slowing their growth and impacting their ability to detect food.
The researchers, from the University of Adelaide, found that while increasing water temperatures might initially make shark embryos develop faster, they subsequently reduce the sharks' metabolic efficiency and make it harder for them to catch prey. Overall, this will result in stunted growth for the animals. Not only that, but the rising of ocean CO2 levels, which causes the water to become more acidic, limits the predators' ability to smell prey, reducing hunting success.
“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,” explains Ivan Nagelkerken, who led the study published in Scientific Reports. “In warmer water, sharks are hungrier but with increased CO2 they won't be able to find their food.”
The scientists conducted the research using mesocosm experiments, where they took large tanks and replicated the natural habitat, including the preferred prey, of Port Jackson sharks. By bringing a small portion of the natural environment into the lab, it allows the researchers to control all of the environmental conditions and manipulate those that they are interested in, in this case temperature and CO2 levels.
What they found was that when ocean temperatures increased on their own, the sharks actually consumed more food as their metabolic rate increased, but when this was done in conjunction with increased CO2 levels, the effects changed. The sharks failed to allocate the extra nutrients gained from the food to growing cells, stunting their growth, while the increase in CO2 also affected olfaction, or their ability to smell prey. This combination of an increased metabolic rate due to higher temperatures matched with a reduction in ability to find the prey pushes the sharks into starvation.
Although only one species of shark was studied in this experiment, due to the common methods employed by other sharks in hunting, researchers think that the same impact will be seen across the board with other species. “One-third of shark and ray species are already threatened worldwide because of overfishing,” says Professor Sean Connell, who co-authored the study. “Climate change and ocean acidification are going to add another layer of stress and accelerate those extinction rates.”
Main image: Klaus Stiefel/Flickr CC BY-NC 2.0