The ocean is a noisy place. If it’s not trendy humpback pop music and chatty narwhals, it’s killer whale death screams and ominous communications from the abyss – not to mention the terrifying acoustic war waged on marine life by humans every day.
But according to scientists, there’s another player in this oceanic orchestra – and it’s something so fundamental to life you could easily forget it was there at all: photosynthesis.
“My goodness we were surprised,” lead researcher Simon Freeman told IFLScience. “Pervasive natural phenomena can be so subtle, sometimes.”
Freeman, along with fellow US Navy oceanographer and spouse Lauren Freeman, first heard the high-pitched ‘click’ of the algae’s photosynthesis back in 2015, while listening to coral reefs off the coast of Hawaii.
Now, eavesdropping on these beautiful but not exactly sprightly structures isn’t as strange as it may seem. The noise coming from a coral reef, Freeman explained, can actually tell you how healthy it is – flourishing, protected reefs feature the low-frequency rumblings of animal life, while degraded reefs have a higher soundtrack, filled with snaps, crackles, and, yes, pops. But while the pair could pinpoint this noise, they couldn’t tell what was behind it.
“We wondered, what mechanism was causing the sound?” said Freeman. “There seemed to be a loose correlation between the sounds and the proportion of algae covering the sea floor.”
To test their algal observation, they designed a simple experiment, described in a paper published in the journal PLOS ONE. They kept some red algae in a tank, free from the flora and fauna it would share its natural environment with, and recorded it with a hydrophone. Sure enough, they heard the tell-tale high-pitched clicks of a coral reef struggling to survive.
“We've gone out snorkeling many times and now often notice bubbles on algae,” said Freeman. “I've been shown videos of Mediterranean sea grass beds bubbling vigorously in the Sun... Why did we not notice this phenomenon acoustically before?”