New study shows that most coral reef sharks eat prey that are smaller than a burger, and typically eat small fishes, mollusks and crustaceans.
Researchers from James Cook University's ARC Center of Excellence for Coral Reef Studies examined stomach contents of reef sharks and conducted chemical analyses of shark body tissue to find out what they had been eating.
Somewhat surprisingly after pumping sharks' stomachs to identify the contents of the last meal, the most common thing to find was in fact, nothing.
"These results suggest that reef sharks eat small meals infrequently and opportunistically," Lead author Dr Ashley Frisch said.
To understand what the sharks were eating over longer periods, the researchers analyzed shark body tissue. They found that the chemical structure of the sharks' body tissue actually matched closely with that of large reef fishes such as groupers, snappers and emperors.
Not apex predators
In turn, this means that reef sharks do not occupy the apex of coral reef food chains, but instead have functional roles similar to those other large predatory fishes.
Co-author of the study, Dr Justin Rizzari, said the new research changes how scientists think about food webs on coral reefs and acts as a reminder that large, conspicuous predators are not always at the top of the food chain.
"We now know that reef sharks are an important link in the food chain, but they are not the last link in the food chain. In most cases, the top predators are tiger sharks, hammerhead sharks, or people," Rizzari said.
In the case of reef sharks, the dietary analyses suggest they should be reassigned to an alternative trophic group such as high-level mesopredators. This change will facilitate improved understanding of how reef communities function and how the removal of predators (e.g., via fishing) might affect ecosystem properties.