Guam Hermit Crab

Calcinus guamensis

The Guam Hermit Crab, known scientifically as Calcinus guamensis, is a small hermit crab species distinguished by its unique coloration and asymmetrical claws. Its body displays a mustard brown or olive hue that transitions to white, while its walking legs are tipped in black. The left claw is noticeably larger and bluish-green, contrasting with the reddish-brown body. This species is native to the tropical waters of the Indo-Pacific, particularly around Guam and Hawaii, and is typically found in coral reefs and rocky areas. It often inhabits tide pools and surge zones, residing at depths from 3 to 20 meters, though it can be found as deep as 80 meters. As a scavenger, the Guam Hermit Crab plays a vital role in maintaining the health of reef ecosystems. It consumes detritus, algae, and small invertebrates, contributing to the breakdown of organic material and the cycling of nutrients, which is crucial for coral reef health. This species is nocturnal, becoming active at night to search for food. It frequently engages in shell-swapping behavior, competing with other hermit crabs for shells that better suit their size, which can lead to aggressive interactions. Although the conservation status of the Guam Hermit Crab has not been assessed by the IUCN, it is an important component of its ecosystem, helping to keep the reef environment clean. Divers may observe this hermit crab's behavior, including its shell-swapping and its role in cleaning the reef. Its nocturnal habits mean it is more easily spotted during night dives.