Acetabularia

Acetabularia · also called Mermaid's Wine Glass, Mermaid's Cup

Acetabularia is a single-celled green alga with a thin, calcified stalk topped by a flat, coin-like cap, giving it the name Mermaid's Wine Glass. Its lone nucleus sits in the base, so a healthy stalk can regrow a lost cap. It draws on calcium and alkalinity, and it is difficult and short-lived in tanks.

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	Polyphysaceae
Native origin	Tropical and subtropical seas; A. crenulata ranges from the Caribbean to Brazil and the Indo-West Pacific
Care difficulty	Advanced
Light	Bright indirect
Pet toxicity	Toxicity unknown

Light

Wants bright reef lighting in a sheltered position, and full-spectrum light is the usual advice. Wild plants grow in very shallow, protected water. Caps are delicate, so choose a bright spot that is out of the main current, rather than simply raising lamp output over the whole tank.

Water

Standard reef parameters: 23-27 C (74-80 F), salinity ~1.025 SG, pH 8.1-8.4. Its stalk is calcified, so keep calcium (~400-450 ppm), alkalinity (8-11 dKH) and magnesium (~1300 ppm) stable; one reference advises slightly above normal calcium and alkalinity. It competes with corals for these.

Soil & potting

Grows from a small holdfast on rock or shell, not in sand. Leave the stalks attached to their rock, even if the caps fall off, because the nucleus sits in the base and the plant can regrow from there. Do not try to tie or glue individual stalks, since they are too thin.

Environment — humidity, temperature, placement

Native to very shallow, sheltered backreef areas. Give it gentle flow in a protected corner of a display or macroalgae tank at standard reef temperature, 23-27 C (74-80 F). Keep snails and hermit crabs away, since they can damage the thin stalks and delicate caps.

Propagation

The cap forms cysts that release swimming gametes, and one study put the A. acetabulum life cycle at about 115 days. Keepers cannot trim or split it. Lost caps regrow if stalks stay attached, and it may seed itself from cysts, but it usually fades quickly in aquariums.

Toxicity detail

No toxicity data for tank animals was found, so the rating stays unknown. One reference lists it as likely reef suitable. It has no strong deterrent: tangs, rabbitfish, sea hares, some snails and urchins are all listed as possible grazers. It poses no recorded smothering risk to corals.

Varieties & cultivars

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

Natural forms1

Mermaid’s Wine Glass

Acetabularia sp. A calcified green alga that grows thin white stalks topped with flat, coin-like green caps. The caps are delicate and easily lost, but they regrow if the stalks stay attached.

Leave the stalks attached to their rock, even if the caps fall off, and keep conditions good so new ones form.