Noctiluca scintillans: plankton lights up the Hobart night

This dazzling Hobart light show signifies the exuberance of life on Earth, right? Not quite.

TWAM-20150711 EMBARGO FOR TWAM 11 July 2015 NO REUSE WITHOUT PERMISSION Bioluminescence, Hobart Pic : James Garlick

The night owls of Hobart were treated to one of the freakiest light shows in nature when a tide of bioluminescent plankton washed ashore in May.

Wherever the water was agitated – where it lapped at the shore, say, or surged over a shallow reef – it glowed neon blue. A handful of lobbed sand splashed down like a shower of sparks; a swimming dog looked positively psychedelic. James Garlick took this 30-second exposure – a finalist in this year’s David Malin Awards – with the Milky Way as a backdrop. It’s tempting to see it as a photo about the exuberance of earthly life, but that’s not quite right. The eerie blue glow is actually billions of organisms starving to death.

Noctiluca scintillans is neither an animal nor a plant, but “in the twilight between them”, says Gustaaf Hallegraeff, a professor of marine science at the University of Tasmania. It’s a dinoflagellate, a single-celled blob barely visible to the naked eye in daylight, with a sticky tentacle that’s used to snare other plankton, fish eggs and larvae. Noctiluca is a “voracious predator”, Hallegraeff says; it forms dense blooms that terrorise and devour microscopic marine life – and when the food is finished, billions float en masse to the surface so the wind can blow them to richer waters. In this case, though, they ended up in Ralphs Bay, a dead end. Within a couple of days they’d starved and every trace of them was gone, their bodies consumed in turn by bacteria.

Why do they light up? No one knows, not even Hallegraeff, who’s studied them for 30 years. Alas, he missed the golden age of funded research during the Cold War. Strange, but true: the superpowers once cursed Noctiluca’s ability to light up a “stealth” submarine like a Christmas tree.