If you see an eerie, glowing blue light dancing across the waves at the beach this New Year’s Eve, don’t be alarmed – though it’s more likely that someone’s kid just broke a glow stick in the water, if you’re lucky it might be caused by bioluminescent algae.
Bioluminescence is the light made within the bodies of living organisms, and it’s super cool. Not just because it looks astonishingly alien, but it also gives off very little heat.
Like a glow stick – which gives off light through chemiluminescence – the chemical reaction in bioluminescence involves two chemicals meeting in the presence of oxygen to produce light.
In bioluminescent organisms these substances are usually compounds called luciferins and enzymes generally known as luciferases. If you think those names sound reminiscent of a certain horned devil, you’d be right, as both are derived from the Latin lucifer: light bearer.
There are at least 11 different types of luciferins, and dozens of associated luciferases, which suggests that bioluminescence has evolved independently many different times across the tree of life. In fact, a recent estimate suggests it has occurred at least 94 times.
By changing the polarisation and microclimate of the luciferins, and by mixing and matching them with structurally different luciferases, organisms can produce different colours of light.
These colours are usually associated with the kind of habitat the organism it calls home: pelagic and deep sea species usually emit blue light, coastal marine species are typically shifted towards green, and freshwater and terrestrial species are more often shifted towards yellow. Though, as always, there are exceptions.
The phenomenon of bioluminescence is found in more than 700 genera across the Earth – from terrestrial plants, to animals, fungi, bacteria, and almost every marine phylum.
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Here are some of those incredible marine organisms that illuminate our oceans:
In a split-second response to threats, many soft-bodied organisms give off a sudden flash when disturbed. Comb jellies (in the phylum Ctenophora) in particular are a perfect example of this.
Flash luminescence is also common in stinging cnidarian jellies. Siphonophores – a group of colonial jellies that includes bluebottles – have even evolved to use light as scare-tactics, lures, and mimics of other species. In particular, Erenna twitches red-glowing filaments to lure small fish.
Sometimes, instead of a single flash there are a propagation of flashes. In the deep-sea crown jellyfish Atolla, this flash races around the body in a circular pattern like a car on a racetrack.
Now, we can’t talk about light-emitting organisms and fail to mention the squids. One species, Vampyroteuthis infernalis (which from Latin translates to “vampire squid from hell”), has two modes of bioluminescence. Mild stimulations evoke a glowing or flashing bright blue light at the ends of all of its arms simultaneously, while a stronger stimulation causes a viscous fluid laced with glowing particles to be emitted from the tips of said arms.
Many fish are also able to glow, and some of them have photophores that appear as lines of small silvery beads in species specific patterns. These patterns may be a way for deep sea fish to tell who’s who, because it’s no good to spend time with species that can eat you or that you can’t mate with. One such example is the lantern fish, which has photophores along its belly and a nasal “headlight” organ.
And back to those glittering blue waves I was talking about earlier. The spectacle is aptly called sea sparkle and is caused by a spherical microalga called Noctiluca scintillans – a Latin name in which aptly means sparkling night light.
Though their blooms are actually a detriment to other species – stripping oxygen and food from the water because these algae don’t photosynthesise – there’s no denying its an incredible sight to behold.
For more science of bioluminescence, and images, see marine biologist Dr Lisa-anne Gershwin’s article “A Light at Sea” in Cosmos Magazine #97 December 2022.
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