Watercress algae
Halimeda tuna
Also known as Money plant, Cactus algae, Coin algae, Calcified green algae, Watercress alga
Care at a glance
- Light
- Medium light
- CO2
- No CO₂ needed
- Growth rate
- Slow
- Placement
- Midground
- Type
- Macroalgae
- Temperature
- 73–81°F (23–27°C)
- pH
- 8.0–8.4
- Max height
- 5.9 in (15 cm)
- Spread
- 7.9 in (20 cm)
- Nutrient uptake
- Water column
- Growth region
- Submersed
- Difficulty
- Medium
- Origin
- A calcified green macroalga of tropical and subtropical reefs in the Indo-Pacific, Caribbean, and Mediterranean, anchored to rock from shallow water down to deep reef slopes.
- Family
- Halimedaceae
Overview
Because it builds a hard skeleton, it needs stable calcium, magnesium, and alkalinity, the same demands as stony corals, plus moderate light and some flow. Wedge it into rock so it can anchor, and keep reef chemistry steady for good growth. Most herbivores ignore it, since the calcified segments are unappealing to eat.
In the wild
Halimeda tuna is built from chains of flat, coin shaped green segments stiffened with calcium carbonate, giving it a jointed, cactus like look. It grows attached to rock and rubble on the reef and holds its shape thanks to its chalky skeleton. In the aquarium it makes an unusual, sculptural macroalga for the display or refugium.
Good to know
Halimeda lays down calcium carbonate as aragonite crystals inside its segments, so the alga is partly mineral. The living tissue is a single continuous cell system threaded through the calcified skeleton.
Did you know
When Halimeda dies its skeleton crumbles into fine white carbonate sand, and over long stretches of time these algae are major builders of tropical reef sand and sediment.
Appears in
Growing Watercress algae?
Track your planted tank, set reminders and plan your layout.
Related plants
Money Plant
HalimedaMedium lightMidground5.9 in (15 cm)
Red Grape Algae
Botryocladia botryoidesMedium lightMidground4.7 in (12 cm)
Caulerpa
Caulerpa proliferaMedium lightBackground5.9 in (15 cm)
Dragon's Breath
Halymenia durvilleiHigh lightMidground11.8 in (30 cm)
Grape Caulerpa
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Chaetomorpha
Chaetomorpha linumMedium lightFloating7.9 in (20 cm)