Coral reef sharks not apex predators

Sydney, Feb 23 (IANS) They may look ferocious but one should not be too worried as coral reef sharks eat prey that are smaller than a cheeseburger.

In the latest study published in the journal Coral Reefs on Tuesday, researchers chemically analysed tissue samples -- via stable isotope analysis -- and examined the stomach contents of more than one hundred white-tip, black-tip and grey reef sharks in an effort to understand the role sharks play in the coral reef food web, Xinhua reported.

"Although black-tip, white-tip and grey reef sharks have long been thought of as top predators, we 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," led author, Ashley Frisch from James Cook University's (JCU's) said.

"This result tells us that reef sharks and large fishes have a similar diet, but they don't eat each other. So rather than eating big fish, reef sharks are eating like big fish," Frisch explained.

With coral reefs decline in response to human-induced climate change and humans killing an estimated 100 million sharks per year, understanding the exact role the important apex predators play in the ecosystem is now more important than ever.

"Humans have a very good habit of interfering in natural ecosystems," Frisch said, such as fishing a particular group of species more so than others, typically apex predators and high-level mesopredators.

The removal of species out of an apex or high level predator in a food-chain will then create a significant top-down effect which influences the population of the lower levels of the food chain, a process known as a trophic cascade, Frisch said.

However, given so many sharks are killed by humans each year, the role that sharks play in the trophic structure of the marine ecosystem has been "a big question".

"Coral reef ecosystems are very complex. The more we look, the more we realise that each and every species plays an important role," the study's co-author Justin Rizzasri said.

"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," he said.

"In most cases, the top predators are tiger sharks, hammerhead sharks, or people."