The discovery was made in the Bay of Rest, a location which also inspired its name, joining the Latin word otium meaning “rest”, with the suffix -ense, meaning “from”.
Like its relatives, P. otiense plays an important role in keeping the mangrove ecosystem thriving. The crabs collect fallen leaves from the mud, dragging them into their burrows to feed on, which stops layers of rotting vegetation from smothering the forest floor.
As they tunnel into their burrows, they also aerate the dense mud, allowing for more oxygen to penetrate the sediments and preventing them from turning anaerobic and toxic. It’s unglamorous work, but without it the mangroves would struggle to breathe.
Among the maze of roots in Exmouth Gulf, P. otiense lives side by side with two other mangrove crab species, P. hartogi and P. holthuisi. While they may share the same patch of mud, they can be told apart by the size, number and arrangement of tiny bumps, or tubercles, on their claws. Not just for show, these bumps make rasping sounds when they are rubbed together, allowing the crabs to communicate with each other.
To confirm that this crab was indeed a new species, researchers examined both its DNA and its physical features. Genetic sequences from the Exmouth specimens were compared with related crabs from across the Indian and western Pacific Oceans. The results revealed a clear difference, confirming that P. otiense had never been described before.
This study is part of an ongoing collaboration between the Biodiversity Research Center, Academia Sinica in Taiwan and the WA Museum’s crustacean team: Andrew Hosie and Ana Hara. Specimens were collected during two major expeditions: Bush Blitz’s 2019 Cape Range Expedition and the WA Museum’s 2016 Pilbara Conservation Systematics’ Exmouth Expedition funded by the Gorgon Net Conservation Benefits Fund.
Now formally described in the scientific record, Parasesarma otiense becomes the tenth known member of its genus in Australia and potentially the third found only in Western Australia. Excitingly, it also represents new species number 200 for the global Ocean Census.
Read the research paper, now published in ZooKeys: https://doi.org/10.3897/zookeys.1255.162897
