Metasesarma aubryi
Common on Orchid Island and Green Island, Taiwan, this rust-red land crab turns up on night walks and shoreline dives year-round in 24 to 30C water.
Look for a rounded, boxy shell in shades of rust-red to brick, often with darker, almost purplish-black claws and legs. It sits low and squat rather than tall-bodied, and the shell surface looks smooth rather than spiny or hairy. Most sightings are on rock and rubble at the shoreline rather than out on open reef, which itself is a strong clue you have the right crab.
This is a shoreline crab, usually spotted tucked among wet rocks and rubble right at the waterline rather than cruising open sand or reef flat. Divers most often log it as common where it occurs, suggesting it holds fairly fixed territory around rock crevices rather than wandering far. It tends to freeze or duck into a crevice when a light or diver gets close, rather than bolt across open ground.
It belongs to the sesarmid family, a group of crabs that live right at the boundary between sea and land, and many species in the family spend more time out of water than in it, which is why you find this one clinging to splash-zone rocks rather than swimming out on the reef.
No clear seasonal pattern shows up in the data, and with a comfortable range of roughly 24 to 30C it seems to be encountered year-round on Taiwan's subtropical coastline. Plan around good sea conditions at Orchid Island or Green Island rather than a particular month.
Taiwan is where this one gets logged, and reliably so: Orchid Island and Green Island between them account for most sightings, with a smaller but steady presence around Kenting. Within these regions divers and snorkellers find it on rocky shorelines and shallow, boulder-strewn margins rather than deep reef.
Mapping where Red Apple Crab is logged…
Taiwan is the place, with Orchid Island and Green Island the two most reliable regions and a smaller presence around Kenting. Look at rocky, boulder-lined shorelines rather than open reef.
There is no strong season in the sighting data. With a comfortable water-temperature range of about 24 to 30C, it appears to be a year-round find on Taiwan's coasts.
Check for a squat, rounded, rust-red to brick-coloured shell with darker, near-black claws, perched low on wet shoreline rocks rather than out on coral. Its habitat choice at the waterline is as useful an ID clue as its colour.
Exact size figures are not confirmed for this species, but like other sesarmid shore crabs it stays small, easily fitting in the palm of a hand.
No. It poses no threat to divers or snorkellers and will typically retreat into a rock crevice rather than confront anyone approaching.
It is a sesarmid crab, a family known for living at the edge of the sea rather than fully submerged, which explains why it turns up clinging to splash-zone rocks instead of swimming out over reef.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
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