Researchers in the Red Sea have discovered a remarkable survival technique that gall crabs use to hide in coral reefs: they use fluorescence to camouflage themselves.
Measuring just one centimetre, gall crabs are a small type of crab that live inside hollows in the coral known as galls. Usually, a certain species of gall crab will always make its home in a particular coral species.
After noticing these crabs glowing on a night dive, researchers at King Abdullah University of Science and Technology (KAUST) decided to investigate the phenomenon further.
- Forget Harry Potter these creatures have real invisibility cloaks
- Birds of paradise ‘glow’ in secret biofluorescent courtship dance
“Gall crabs are one of the many types of invertebrates living in association with corals on tropical reefs,” says Francesca Benzoni, associate professor of marine science at King Abdullah University of Science and Technology (KAUST).
“Much remains to be discovered on cryptic and poorly studied reef invertebrates and their fundamental biology, ecological role, and the role they play in the resilience of coral reef ecosystems in the Red Sea and worldwide.”
KAUST marine science PhD student Susanne Bähr knew that many types of reef fish fluoresce for different reasons – including for visual communication, camouflage and recognising mates. So, when she noticed the gall crabs fluorescing, “this observation was particularly intriguing,” she says. “I wondered if we could find similar patterns in crustaceans as we’ve observed in fish.”
- Rainbow animals: a dazzling display of colourful fur, feathers and scales
- Why do crabs walk sideways?
The team collected 286 gall crabs from 14 different groups in the Red Sea and Indian Ocean and identified which parts of different crabs fluoresced. Different species of gall crabs have different types of dens – for example, an open tunnel compared with an enclosed hollow – and the researchers noticed that the pattern of fluorescence impacted how visible they were in their little hidey-holes.
For example, some species of gall crab live in cylindrical coral pits. “The back of the crab is sticking out a little bit. It has this striking fluorescence pattern that disrupts how the crab looks,” says Bähr. “It disguises the crab's outline, so you can’t see a crab shape.”
This led the scientists to the hypothesis that this fluorescence evolved as a way of helping the little crabs camouflage themselves while inside their coral home. This ability could help them keep out of sight of predators and stay safe in their coral hideout.
There’s still much more to learn about these peculiar crustaceans, including what role they might play in protecting vulnerable coral reefs. “I want to use my research to highlight the importance of these coral-associated invertebrates and their significance for coral reef ecosystems,” says Bähr.
“They’re generally overlooked, and we need to understand how many there are, why they’re there, and what they do for reef persistence and resilience.”
Image and video credit: King Abdullah University of Science and Technology (KAUST) Habitat and Benthic Biodiversity Laboratory
More amazing wildlife stories from around the world
- More than 100 swamp alligators caught in Georgia – something worrying has been found in their blood
- 100-million-year-old fossil found INSIDE belly of gigantic dinosaur in Australian desert
- 83 whale bone tools pulled from Bay of Biscay caves are oldest ever discovered
- Scientists stunned to see humpback whales trying to send messages to humans
