‘Cosmic’ bioluminescent algae lights up Melbourne’s St Kilda beach

Beachgoers in Melbourne have been treated to the “cosmic and magical” sight of bioluminescent algae off St Kilda beach this week.

Richard Pensak, a marine biologist at local environment group Earthcare St Kilda, spotted the bright pink-coloured cloud in the water on Sunday, and immediately knew what it was.

When he returned to the water after dark, crowds had already gathered to see the “really pretty and sparkly” spectacle.

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“It just lights people up,” Pensak said.

Bioluminescent algae is a rare but not unprecedented sight in Port Phillip bay. The natural phenomenon, known as “sea sparkles” or “red tide” is caused by an algae called noctiluca scintillans: beautiful to look at but potentially irritating to fish due to high levels of ammonia and reduced oxygen levels in the water.

Pensak described seeing the effect first-hand as a “bucket list” item, while acknowledging its flipside – that the algae’s expanded range is associated with rising ocean temperatures.

Ryan Abramowitz, a local author and illustrator, described the iridescent blue of the algae rippling on the water’s surface as “awe-inspiring” and like “shimmering galaxies whirling and swirling across the shore”.

Visiting the beach on Monday evening, he splashed through the cold early spring water to see the “stunning rhythmic trails” of light.

“I go for night swims all the time, but this was definitely the most cosmic and magical,” he said, “an exquisite unfolding for the first day of spring”.

Abramowitz said he had seen bioluminescent algae before in Sydney and Bali, but never before in Melbourne.

First documented in Sydney Harbour in 1860, the bioluminescent algae has become a much more common sight in Australian waters since the 1990s, particularly in Sydney and Tasmania.

Prof Shauna Murray, an algae expert and marine biologist at the University of Technology Sydney, said the species had proteins called luciferase that enabled it to glow at night.

The phenomenon is quite common along Australian coasts, she said, and a natural part of the ecosystem, expanding farther south into Tasmania due to warming waters off the east Australian current.