Australia’s beaches are glowing electric blue—and science explains why

It isn’t unusual to see beaches lit up during an evening stroll on summer vacation, often from bars, restaurants, and other attractions along the promenade.

At St Kilda Beach near Melbourne in Australia, however, a “magical” and “ethereal” blue glow has been spotted coming from the water itself. While it might sound like something out of a sci-fi movie, it is actually a completely natural phenomenon which occurs in numerous parts of the world.

The science behind the glow

Bioluminescent algae, which appear as bright pinkish-orange clouds during the day, are responsible for the stunning underwater light show at night.

Richard Pensak, a marine ecologist who works in St Kilda, was the first to discover the presence of the algae, which is unofficially referred to as “sea sparkle.”

Pensak explains that the electric blue hue covering the water and sand results from a chemical reaction that occurs when algae are disturbed or agitated. In many cases, this happens when a predator disturbs them, but it could also be caused by sharp movements in the water, including waves, swimmers, or boats.

A defense mechanism

According to Pensak, the phenomenon is “likely a defense mechanism” used by algae to fend off predators, either directly or by attracting larger predators that target their smaller attackers.

While the algae are not believed to be toxic to humans, they can be dangerous for fish due to high levels of ammonia, an inorganic chemical compound of nitrogen and hydrogen, and their ability to lower oxygen levels in the water.

A sign of changing oceans

Bioluminescent algae have become more common and larger in size since the 1990s, Pensak says, as a direct result of rising ocean temperatures around the world, which create conditions for them to flourish. “It can be a sign of an unhealthy ocean,” he summarized.

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