That fire corals are not actually corals but animals called hydrozoans more closely related to the sinister, tentacle-trailing Portuguese man-o-war is not the most interesting thing about them.
Nor is it that they leave anyone who touches them with a strange, burning sensation as a result of the stinging cells embedded in their skeletons that inject venom into their victims.
What is most intriguing about them is their ability to grow in two completely different ways and what that means for the environment in which they live.
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Fire corals, like numerous marine species such as other corals, sea anemones and many shellfish, can’t move – they are described by scientists as sessile, anchored to the seabed or other substrates.
They feed on passing organisms such as zooplankton, animals ranging from single-celled organisms to tiny crustaceans such as copepods that drift in the sea currents.
As the prestigious journal Science reported, fire corals either look like sheets of organic matter that grow on rocks or they can adopt a more tree-like formation, resembling a wacky plant that you might imagine growing on an alien planet. Either way, they do create – like true corals – a calcareous skeleton in which the living polyps dwell.
But (in contrast to true corals) fire corals adapt to what’s taking place within their reef habitat by changing their shape. Studies show that when hurricanes destroy other reef dwellers such as macroalgae, fire corals quickly move in and colonise the vacant spots.
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“And when the reef gets crowded, fire coral sprouts into its branching tree form, so it can continue to thrive in tight spaces and provide an upright structure that other organisms nibble on, live in, or otherwise use,” it carries on.
“In a world with frequent storms and stiff competition for space on the bottom, fire corals are poised to inherit the shallow reefs,” says the researcher Peter Edmunds who carried out the study that showed how their unique adaptability was giving them the edge.
The cells that can deliver a nasty sting to the unwary diver are also, of course, essential for how fire corals survive – they also use them to paralyse their zooplankton prey and then draw the morsels into mouth openings.
But (again like true corals, even though they’re not), fire corals also get their energy needs from a mutualistic association with symbiotic algae – the algae benefit from the shelter provided by the hard skeleton, while at the same time transferring some of the sugars and amino acids produced through photosynthesis to the fire corals.
To sum up: when is a coral not a coral? When it’s a fire coral. But it still looks and largely behaves like a coral.
