Photographers in Australia have been sharing stunning photographs of beaches glowing iridescent blue. The photos, taken in Preservation Bay on the North West coast of Tasmania, show the water close to the shore illuminated, as if lit from below. The spectacular natural phenomenon, known as bioluminescence or "sea sparkle", is typically seen in calm waters.

It is caused by billions of single-celled algae or plant plankton, called Noctiluca scintillans , which emit light as a defence mechanism when they are disturbed by waves or currents. Gustaaf Hallegraeff, a professor in aquatic botany at the University of Tasmania, told ABC News the flashing mechanism is deployed to scare off predators.

"There's actually evidence that shows if you offer an animal a choice between a luminescent plankton and a non-luminescent plankton, they avoid the luminescent one," he said. While bioluminescence is not harmful to humans, it can act like a "vacuum cleaner" disrupt the food chain of other marine species, such as shellfish, if present in large quantities.

Prof. Hallegraeff said that ocean currents and the warming of the oceans may have contributed to the spread of bioluminescence in recent years.