Quiet reefs keep life away
A new study shows damaged reefs can be too quiet to attract new juvenile fish.
Dr Mark Meekan from the Australian Institute of Marine Science (AIMS) says listening to a healthy coral reef through underwater microphones is like “listening to bacon frying in a pan”.
Normally, the sound of a living reef is “punctuated by the chirps and tweets and all sorts of screeches that come from fish”.
But when coral is harmed by bleaching or cyclones, they “lose their zooxanthellae, they starve to death, they die and live coral cover is replaced by algae”, Dr Meekan said.
“Those young fish graze the reef and keep the algae down. Without the fish suppressing the growth of algae, the corals have essentially no space on the reef and can't get through.”
According to a new paper in the Proceedings of the National Academy of Sciences, reefs off the coast of Queensland hit by Cyclone Ita in 2014 and Cyclone Nathan in 2015 saw “the most severe global mass-bleaching event on record” in 2016.
New recordings show the damage “significantly reduced acoustic complexity, richness and rates of invertebrate snaps” when compared to earlier recordings.
Dr Meekan says it interrupts the lifecycle of fish that spawn in the open water before heading back to the reef.
“Baby fish that have been drifting off into the open water have to find their way back home, and what they use is sound,” he said.
“Turns out that the sounds of the degraded reef — the reefs that have undergone the bleaching and the cyclones — are both much quieter and much less attractive to the baby fish.”