Coelarthrum

Coelarthrum · also called String-of-Pearls

Coelarthrum is a red macroalgae built from chains of fluid-filled, bead-like segments, which gives the kept form its name, String-of-Pearls. It looks much like Botryocladia but is pinker and has no obvious stolon. It is rarely kept, and keepers have little experience with its care.

Educational only. Some KinStation entries are reviewed by licensed veterinarians, but none can replace an in-person exam. Always consult a licensed veterinarian or board-certified specialist for diagnosis, treatment, or any decision affecting your pet's health.

Quick facts

Category	Marine & Algae
Family	Rhodymeniaceae
Native origin	Documented species: Indian Ocean and Australian coasts; kept form unrecorded
Care difficulty	Intermediate
Light	Medium light
Pet toxicity	Toxicity unknown

Light

Keepers have little experience with its light needs. Its lookalike Botryocladia does well under moderate reef lighting and can bleach under very intense light, so moderate, steady light is the sensible start. Raise intensity slowly and watch the beads for fading.

Water

Standard reef parameters: 23-27 C (74-80 F), salinity ~1.025 SG, pH 8.1-8.4. No specific needs are recorded. Keep salinity steady and change conditions slowly. Measurable nitrate and phosphate are a better starting point than very low nutrients, as with most kept red algae, and iron or trace dosing is untested on it.

Soil & potting

Treat it as an attached alga that grows on hard surfaces, not in sand. It has no pronounced stolon to creep along rock, so anchor the base gently with line against rubble or wedge it between rocks. Avoid pinching the beads when you handle or secure it.

Environment — humidity, temperature, placement

Documented species come from the Indian Ocean and Australian coasts, and the origin of the kept form is not recorded. Moderate flow that keeps debris off the beads, at standard reef temperature of 23-27 C (74-80 F), is a cautious start in a display or macroalgae tank.

Propagation

Keepers have little record of propagating it. A short chain of beads can be trimmed and tied to rubble, and research on C. opuntia shows this genus can respond to wounds and regenerate. Handle chains gently and make clean cuts, then leave the piece undisturbed.

Toxicity detail

No toxicity data for tank animals was found, so the rating stays unknown. No grazing deterrent or coral smothering risk is recorded. The lookalike Botryocladia is generally left alone by herbivores, but that should not be assumed here. Remove any collapsed beads to protect water quality.

Varieties & cultivars

Natural forms are the wild species; cultivars are selectively-bred colour or variegation forms of the same plant.

Natural forms1

String-of-Pearls

Coelarthrum sp. Chains of fluid-filled, grape-like bladders give this red alga its name. It looks much like Botryocladia but is far pinker and lacks the obvious stolon.

Little is recorded about its care, so keep conditions stable and change lighting gradually.