JEDDAH: Marine researchers from the King Abdullah University of Science and Technology have discovered that gall crabs use highly evolved fluorescence to help conceal themselves within coral hideouts.
Susanne Bahr, a KAUST marine science doctoral student, observed that gall crabs fluoresce during night dives, according to a recent report.
Bahr said: “I had been working with these crabs for some time, so this observation was intriguing. I started reading about fluorescence.
Bahr and colleagues collected 286 gall crabs from 14 genera, sampling from all known host coral genera in the Red Sea and Indian Ocean. (Supplied)
“It’s well-studied in reef fish, which have many functions, but less is known about fluorescence in crustaceans. Crabs and shrimps are very diverse, so I wondered if similar patterns occur in crustaceans as in fish.”
Bahr and colleagues collected 286 gall crabs from 14 genera, sampling from all known host coral genera in the Red Sea and Indian Ocean.
They developed an imaging technique to identify which parts of the crabs fluoresced and how much. They also performed a morphological analysis and built an evolutionary tree based on genomic sequencing.
Gall crabs do more than just live among corals: they have a strong symbiotic relationship. Some invertebrates hide in coral branches and crevices, but for gall crabs, the connection is deeper, the report said.
The researchers suggest that fluorescence evolved in various gall crab species to help camouflage them in their coral dwellings. Different species inhabit different coral structures — such as open tunnels or enclosed galls — and their fluorescence patterns influence their visibility.
Bahr gave an example of a species living in cylindrical coral pits. “The back of the crab sticks out slightly. Its fluorescence pattern disrupts its outline, disguising its shape.”
Francesca Benzoni, Bahr’s supervisor at KAUST, emphasized the importance of understanding coral reef ecosystems. “Gall crabs are among many invertebrates living with corals on tropical reefs,” she said.
Benzoni added: “Much remains to be discovered about cryptic and poorly studied reef invertebrates, their biology, ecological role, and their contribution to coral reef resilience in the Red Sea and worldwide.”
Bahr said: “I want my research to highlight the importance of coral-associated invertebrates and their role in coral reef ecosystems.”
“They are often overlooked, and we need to understand their abundance, reasons for presence, and their role in reef persistence and resilience.”
