Sharks will likely become much smaller and less aggressive hunters under the rising CO2 levels and warming oceans associatedwith climate change, according to a study published in Scientific Reports by University of Adelaide researchers. In large-tank laboratory experiments with Port Jackson sharks — a bottom-feeding variety that primarily relies on smell to find food — the researchers found that the combination of warmer water and high CO2 increased the sharks’ energy requirements and reduced their metabolic efficiency. Elevated CO2 levels also dulled the sharks’ sense of smell to the point that they were unable to locate prey — a finding confirmed in previous CO2/olfaction studies. Together, these effects led to dramatic reductions in the sharks’ growth rates. “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,” said lead researcher Ivan Nagelkerken.