Sharks are going to have a tougher time hunting prey in the warmer, more acidic oceans of the future, according to new research.
Australian scientists put Port Jackson sharks into large tanks and cranked up the temperature and levels of dissolved carbon dioxide in the water to simulate what their natural habitats are expected to look like by the end of the century. Then they hid (dead) prey in trays of sand, and timed how long it took for the sharks to sniff it out and dig it up.
(These researchers might have the best job in the world. Who wouldn’t want to hang out and watch a shark tank all day long? And Port Jackson sharks, even among sharks, are pretty damn awesome-looking.)
The study actually contradicts earlier research that suggested warmer ocean conditions would cause sharks to eat more, resulting in greater hunting pressure on lower levels in the food chain.
It’s true that sharks are hungrier in warmer water — they both have greater calorie requirements and metabolize less efficiently. Earlier research as well as this new study confirms that given unlimited access to food, sharks eat more as the temperature rises.
But a more-acidic ocean affects a shark’s sense of smell. It could mean that even though they are hungrier, they will have a harder time finding prey, and would end up eating less. The combination of these two could lead to very hungry sharks.
In the experiments, sharks that grew up in CO2-rich water took four times (!) as long to find their food.
“With temperature-driven increases in metabolism, the likelihood of predator starvation increases when it is not matched by elevated ingestion rates; in some cases (such as the juvenile hammerhead) sharks are at provisioning limits and these stresses could push them into starvation,” the authors write.
Spending more time looking for food costs more energy, and it also leaves the sharks more vulnerable to attack from even bigger predators, like wobbegong sharks and seals.
Anything that affects a predator and its relationship to prey can have complex and not-well-understood implications for the ecosystems where they live. (Remember what happened when wolves were re-introduced to Yellowstone?)
Small sharks like the Port Jackson serve as both predator and prey, and climate change will very likely affect the food webs they are tied to in dramatic ways. Climate change is going to change these little guys’ world inevitably, but hopefully they prove to be adaptable, and humans of the future will still get to observe them in the wild, not just in laboratory and aquarium shark tanks.