Rare species of crab never sighted in WA before found at Broome reef

A rare species of crab that has never been sighted in Western Australia has been spotted among rocks at low tide in Broome. Broome local Sharmaine Donnelly was exploring Entrance Point last month when she came across a pair of unusual-looking crabs no more than 6cm long. After posting photos of the crabs to a crustacean identification group on Facebook and contacting an expert from the WA Museum, Ms Donnelly realised she had made a significant discovery. “(The expert) came back and said it was a Rathanbunaria orientalis and that it is very rare — only ever been sighted in Queensland and Singapore, never Western Australia,” she said. “He was really excited, so I posted it on iNaturalist (website) and got a lot of responses saying it definitely was a Ranthanbunaria orientalis.” Valentine de Mazancourt from the National Museum of Natural History in Paris, who specialises in the systematics of amphidromous crustaceans of the Indo-Pacific region, verified the rare finding. “There are very few records of this species globally; one in Singapore, one in Palaur and a few in Australia: Cape York and Thursday Island,” he said. “Given the known records, this species is expected to have a rather large distribution in the central Indo-Pacific area but seems to be uncommon. Mr de Mazancourt confirmed while the crab was always found in association with corals, this was the first and only documented record from Western Australia and the Indian Ocean. When observing the pair of crabs, Ms Donnelly said they stood out to her because they resembled the Spanish dessert, churros, but were very timid. “I have a habit of picking up rocks on the reef and looking underneath, because that’s where you find all the interesting marine life, and I picked it up and saw a couple of crabs running away and trying to hide from me,” she said. “So I grabbed the camera and took a couple of snaps, but they were very shy.” Ms Donnelly said she had been back to Entrance Point to look for them again but had not seen them since. “I feel very excited because it’s a Western Australian first and it’s never been documented in WA before, and even on iNaturalist it’s the very first recorded observation,” she said.