AquaticCare difficulty: AdvancedLegal complexity: Low

Mertens' carpet anemone

Stichodactyla mertensii · also called Merten's carpet anemone, Mertens' sea anemone

The largest sea anemone known, with a disc that may exceed a metre, and unusual among big carpets in gripping rock or coral instead of sitting on sand. Keeping it means strong light, frequent meaty meals and a huge tank, and wild animals host at least 13 anemonefish species. Its sting is severe enough to damage corals and any fish other than a clownfish, so nothing should sit close to it. Treat it as able to injure people: a 2015 case report describes prolonged, reversible neurological symptoms in a pet store worker stung by a carpet anemone, and S. haddoni has caused anaphylactic shock. It may also eat small fish.

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Quick facts

Size	Regarded as the largest sea anemone, with a disc over 1 m across; one reference gives 90 cm as typical, up to 150 cm. Tentacles are about 1-2 cm.
Lifespan	—
Social needs	solo
Native region	Indo-West Pacific, from Mauritius to Fiji and from southern Japan to Australia
Origin	Old World
Climate	Tropical
Water type	Marine
Family	Stichodactylidae
Genus	Stichodactyla

Part of the Sea Anemones

Stinging, sessile cnidarians ranging from clownfish-hosting giants to nano-sized carpet species. Many are demanding, mobile, and can sting corals or be drawn into pumps — careful placement and rock-stable water are essential.

Beaded sea anemone Bubble tip anemone Carpet anemone Christmas anemone Condy anemone Haddon's carpet anemone Hell's fire anemone Hemprich's sea anemone Long tentacle anemone Magnificent anemone Mini Maxi Anemone Pizza anemone Rock flower anemone Sebae Anemone +2 more →

Color & pattern variants

Natural variants occur in the wild; selectively bred (man-made) variants were developed in captivity.

Natural

Gold Tip Mertens' Carpet →

Named for gold-coloured tips.

Yellow Spark Mertens' Carpet →

A hobby colour name that points to yellow tones. No fuller description is on record.

Habitat & enclosure

Provide strong light, moderate flow and stable rock for its foot in a very large tank. One care reference gives 100 gal (380 L) as the floor, and an adult will outgrow that. In the wild it sits on rock, coral and rubble on reef slopes at about 1 to 20 m, between Mauritius and Fiji and from southern Japan down to Australia.

Keep stable reef water: SG about 1.025, 24-27 °C (75-81 °F), pH 8.1-8.4, with low phosphate.

Substrate

Provide stable, well-secured rock or rubble for the foot. Unlike S. haddoni it does not need open sand, but the rockwork must not shift under its weight.

Equipment & setup

Use strong reef lighting across a wide area and moderate flow. Guard pump intakes, run a capable protein skimmer and keep the rockwork secure.

Diet

Relies on light and on food. Like other carpet anemones it keeps zooxanthellae, so it needs strong lighting, and it also takes meaty food. Offer pieces of fish several times a week, as one care reference finds it prefers fish flesh to crustacean meat. It may also eat small fish in the tank.

Behavior & temperament

It drapes over hard surfaces on the fore reef, unlike its sand-living relatives. It is not choosy about partners, with 13 or more anemonefish species on record plus the three-spot dascyllus. Field observations have also recorded it reproducing asexually.

Health

Stings hard. Corals and any fish other than a clownfish are at risk, as with other big carpets, and it may eat small fish. Treat it as able to injure people. A 2015 case report describes prolonged, reversible neurological symptoms in a pet store worker stung by a carpet anemone, and S. haddoni has caused anaphylactic shock. One reference calls its tentacles non-sticky and repeats the nickname non-stinging carpet anemone, yet the same page warns that it stings whatever it touches, so ignore that nickname. Loss of colour points to bleaching. If a large anemone dies, remove it quickly, because it can foul the water.

Tips, DIY & hacks

Add it before fixed corals so it can pick its spot, then keep corals out of its reach. Its sting can damage corals and any fish other than a clownfish, so keep a clear gap around it. It may eat small fish. Plan for its full size from the start. Treat it as able to injure people, and wear gloves when working near it.