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Alumni explainer: the science behind sea sparkles

Gustaaf Hallegraeff

What causes the sea sparkle spectacular that light up Tasmanian and New South Wales beaches?

We asked alumnus Emeritus Professor Gustaaf Hallegraeff of the Institute of Marine and Antarctic Studies (IMAS) at the University of Tasmania.

Bioluminescent spectacles are caused by the plankton Noctiluca scintillans [“scintillating night light”, or “sea sparkle”].

The causative organism is a microscopic dinoflagellate, neither an animal nor a plant but in the twilight between them, something scientists call a “protist”.

These single celled, bubble-shaped forms, 0.5 to 1 mm in diameter, carry a sticky tentacle used to snare away other plankton that come too close.

When they were first discovered in 1810 this caused them to be mistaken for small jellyfish.

Noctiluca have no means of locomotion but can adjust their buoyancy to forage through the water column.

When the food is finished, billions float to the surface in the hope of being carried by wind or currents to richer waters.

If they end up washed ashore by onshore winds, the death throes of billions of stranded protists, stirred up by breaking waves create a spectacular light show. What a way to go out.

These little fireworks have nothing to do with the chemical element phosphorus but use a molecule luciferin, an enzyme called luciferase, which combined with oxygen generates neon blue light.

For sea creatures such as Noctiluca, the use of bioluminescence is thought to act as a burglar alarm to scare off predators.

Ironically, almost everything we know about bioluminescence dates from Navy-funded research during World War 1 when a stealth German submarine tried to sneak through the Strait of Gibraltar, but lit up like a Christmas tree and was sunk by Allied forces.

Despite all the research, these neon blue spectacles are tough to forecast with precision.

The first bioluminescent spectacle in Australia was reported from Sydney Harbour in 1860, but Noctiluca blooms became more common off Sydney from the 1990s, and started to regularly drift southwards expanding their range into Tasmanian waters from the 2000s.

Increasingly, travellers from all over the world arrive on our shores to admire the glorious show of sea sparkles in our oceans.

In daytime you can recognise Noctiluca as pink slicks, but unlike other types of algal blooms this organism is essentially harmless to humans.

Your best bet to see it is to check for tip-offs on the Bioluminescence Tasmania Facebook page.

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Published on: 10 Jun 2021 11:24am