Scientists studying reefs off Australia on Friday said sharks play a fundamental role in the health of coral and overfishing of them made reefs more vulnerable to global warming and weather disasters.
A research team, led by Mark Meekan from the Australian Institute of Marine Science (AIMS), studied the impact of sharks at the Rowley Shoals and Scott Reefs 300km off northwest Australia over 10 years.
“Where shark numbers are reduced we see a fundamental change in the structure of food chains on reefs,” Meekan said.
When coral dies algae grows over it, compromising coral’s ability to regrow.
Meekan said the herbivorous fishes chewed out small spaces so regrowth could take place.
The study compared the impact of cyclones and bleaching events on the marine-protected Rowley Shoals, where fishing is banned, with the neighboring Scott Reefs, where Indonesian fishermen are allowed to catch sharks.
It found less coral and more algae on the fished reefs after a major disturbance, which Meekan said was significant as the pressures of global warming increased.
The findings showed that declining global reef shark populations due to overfishing was of “great concern” because it would leave the coral structures more vulnerable to bleaching events from warmer, more acidic oceans and to large cyclones, Meekan said.
A major AIMS study last year of the Great Barrier Reef, off Australia’s east coast, found that coral cover had more than halved in the past 27 years due to storms, bleaching linked to climate change and the predatory crown-of-thorns starfish.
According to the team their shark study, published in the latest edition of peer-reviewed scientific journal PLOS ONE, had offered a “unique opportunity” to isolate and examine the impacts of sharks on an entire reef ecosystem’s health in a way not attempted before.