Depth
Acetabularia · Plants, Algae & Seagrass

Mermaid's wine glass

Acetabularia acetabulum

0-40m
Depth Range
Variable
Max Size
Mediterranean
Distribution
0-40m
Depth Range
Variable
Max Size
Reef & Open
Habitat
Photosynthetic
Diet
Meadow-forming
Social
LC
IUCN Status
Kingdom Plantae
Division Tracheophyta
Genus Acetabularia
Species acetabulum

Marine Plant

Identification & Biology

  • IdentificationA tiny, distinctive single-celled green alga shaped like a small umbrella or wine glass on a slender stalk. Bright green. Each individual is a single giant cell, making it one of the largest single-celled organisms in the world.
  • SizeHeight up to 5 cm. Cap diameter up to 1.5 cm. Each individual is a single cell.
  • Social HabitFound in groups on rocky surfaces in shallow, sheltered water. Each wine glass is one giant cell with a single nucleus in the base.
  • HabitatShallow, sheltered rocky pools, harbour walls, and calm coastal areas with clear water.
  • Depth0 to 10 m. Most common in very shallow, well-lit water.
  • Feeds OnPhotosynthetic. Produces its own food from sunlight, carbon dioxide, and dissolved nutrients through photosynthesis.
  • DistributionMediterranean Sea and adjacent eastern Atlantic. Present in Maltese sheltered bays and rock pools.
  • DescriptionAcetabularia acetabulum is one of the most remarkable organisms in the sea. Despite looking like a tiny umbrella, each individual is a single giant cell containing one nucleus located in the base of the stalk. This makes it one of the largest single-celled organisms on Earth. It has been extensively used in biological research to study how the nucleus controls cell development.

Range

Habitat & Distribution

Found across the Mediterranean, inhabiting reef & open environments. Active from the surface down to 40m depth.

Where Malta divers have spotted this species

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Sightings are logged by divers using our What Did You See? dive-log tool. View the full live sightings map.

Detail

Preferred Environment

Reef & Open habitats, typically at depths of 0-40m. Most commonly encountered by divers at the shallower end of its range.

Encounter Tips

Best approached slowly and calmly. Avoid casting shadows directly over the animal. Neutral buoyancy and patience increase encounter success significantly.

Mermaid's wine glass species card

Biology

Behaviour & Diet

Feeding Strategy

Produces energy through photosynthesis using sunlight penetrating the water column. Forms dense meadows that are critical nursery habitat and oxygen producers for the Mediterranean ecosystem.

Photosynthetic

Reproduction

Reproduces vegetatively and sexually. Vegetative growth is the dominant strategy; sexual reproduction is seasonal and infrequent.

Seasonal spawning

Behaviour & Defence

Posidonia and other Mediterranean seagrasses form protected meadows under EU Habitats Directive. These habitats are sensitive to anchor damage, trawling, and water quality. Recreational divers should avoid contact with the meadow.

Defensive

Dive with diveshack

Where to Encounter in Malta

The following dive sites offer strong habitat match for Acetabularia acetabulum. All are accessible on a guided dive with diveshack.

5-30m
North Malta

Cirkewwa

Rocky reef with caves, arches and ledges hosting a rich diversity of reef species.

View dive site ›
5-50m
Gozo

Blue Hole

One of the Med's most famous reef dive sites. Rocky walls and archways covered in life.

View dive site ›
18-36m
South Malta

Um El Faroud

The wreck lies on a sandy bottom surrounded by rocky reef -- a diverse habitat attracting reef species.

View dive site ›
IUCN Red List Least Concern

Conservation Status

This species is assessed as Least Concern on the IUCN Red List. Mediterranean populations face ongoing pressure from fishing activity, habitat degradation, and climate-driven changes to prey availability.

Source: iNaturalist Guide #888
by Lesley Clements (CC BY-SA)
diveshack Mediterranean Marine Life guide