Coleman Shrimp

Locating a Coleman shrimp requires carefully scanning venomous fire urchins (*Asthenosoma varium* or *Asthenosoma intermedium*) on tropical reefs. Once a host urchin is spotted, examine its surface for a distinct bare patch cleared of spines, where a pair of shrimp—a larger female alongside a smaller male—typically perches.

Because host fire urchins carry painful, highly toxic spines, strict buoyancy control is essential. Maintain a safe distance and never rest your hands or gear near the host substrate. While some cleaner shrimp species willingly climb onto a diver's hand, you should never attempt this with *Periclimenes colemani* due to the severe hazard posed by the urchin's venomous spines. Approach slowly and calmly to avoid startling the host urchin or causing the shrimp to retreat beneath the surrounding spine canopy. When photographing these macro subjects, set camera focus and lighting beforehand to avoid prolonged exposure to bright underwater lights.

Because *Periclimenes colemani* is a stationary, non-migratory species reliant on its host urchin, encounters are possible throughout the year across its Indo-Pacific range. Finding them relies on regional diving conditions, surface sea state, and the local abundance of healthy *Asthenosoma* fire urchins rather than seasonal animal migrations.

In major macro-diving destinations such as Anilao in the Philippines and various Indonesian regions including Komodo, Alor, and Timor, sightings occur consistently in all months. Local dry seasons generally offer optimal diving conditions, featuring calmer seas and enhanced underwater visibility for macro spotting. Along the Great Barrier Reef in Australia, diving is conducted year-round, with the settled weather between May and November providing exceptionally stable surface conditions. Because individual host urchins remain in localized areas for long periods, local dive guides are often able to locate specific pairs across multiple seasons.

*Periclimenes colemani* is distributed across the tropical waters of the Indo-Pacific, with documented sightings spanning Indonesia, the Philippines, and Australia's Great Barrier Reef. Its depth range extends from shallow coastal zones at 1 to 5 metres down to depths of roughly 30 metres on deeper reef slopes.

This species is an obligate symbiont and does not inhabit open reef substrates or free-standing corals. Its habitat is defined entirely by the presence of host fire urchins, notably *Asthenosoma varium* and *Asthenosoma intermedium*. These venomous sea urchins inhabit a variety of marine environments, including coral reef slopes, sandy rubble patches, drop-offs, and muck-diving substrates. Within this specialized microhabitat, the Coleman shrimp resides directly on the host urchin's test within a dedicated area cleared of spines, benefiting from the formidable defensive umbrella created by the host's toxic primary spines.

The diet of *Periclimenes colemani* consists primarily of algae, microscopic parasites, and planktonic organisms. Positioned on the cleared patch of the host urchin's shell, the shrimp uses its long, slender arms and small pointed claws to pick at drifting organic matter, microscopic debris, and suspended plankton from the surrounding water column.

In addition to filtering waterborne particles, Coleman shrimp consume microalgae growing on or near their host and may feed on parasites or mucus present on the urchin. They are also opportunists that readily consume nutritional scraps stirred up or discarded during the host urchin's movements across the seabed. Feeding takes place throughout the day and night as currents carry food particles past the urchin. Unlike free-swimming cleaner shrimp that operate broad cleaning stations for client fish, the Coleman shrimp's foraging is almost strictly confined to its immediate area on the host urchin.