TankBud

Mertens' carpet anemone

Stichodactyla mertensii

Also known as Mertensii Carpet Anemone, Giant Carpet Anemone

SaltwaterAnemone

Mertens' carpet anemone (Stichodactyla mertensii)
Brocken Inaglory · CC BY-SA 3.0

Care at a glance

Temperature
75–81°F
24–27°C
pH
8.1–8.4
Adult size
35.4 in
90 cm
Minimum tank
53 gal
200 L
Temperament
Aggressive
Social behavior
Solitary
Tankmates
With caution
Swim level
Bottom
Difficulty
Difficult
Breeding
No record
Rarity
Rare
Reef safe
Reef safe with caution
Family
Stichodactylidae
Origin
Indo-Pacific reefs (Red Sea to French Polynesia)

Overview

Needs strong, stable lighting and vigorous flow across its whole surface, plus weekly feedings of large meaty items like squid, shrimp, or silverside once it is established. It carries a powerful sting and, unusually for a carpet anemone, is genuinely aggressive toward tankmates: give it at least a foot of clearance from any other coral or anemone, and never let it settle near a powerhead intake it could get drawn into. Clark's clownfish and ocellaris are among the most commonly seen hosts, and in the wild it accepts a broader range of anemonefish species than any of its relatives. Because of its eventual size this is a long term commitment best suited to a large, mature display; acclimate it slowly and give it a stable home from the start, since repositioning a settled adult is difficult and stressful for the animal.

In the wild

Ranges widely across the Indo-Pacific from the Red Sea to French Polynesia, where it attaches to hard reef substrate rather than burying in sand the way Haddon's and gigantea carpets do. It is the largest sea anemone in the hobby by surface area, with a mature specimen capable of covering close to a meter of reef, so it needs a large footprint of rock or reef base to settle onto and years of room to grow into. It hosts a broader range of clownfish species than any other carpet anemone.

Good to know

Stichodactyla mertensii holds the record as the largest known sea anemone species, with an oral disc that can exceed a meter across, larger even than Heteractis magnifica. It draws most of its energy from symbiotic zooxanthellae, reproduces both sexually and by fission, and hosts more anemonefish species than any other single carpet anemone, including several Amphiprion species not recorded on any other host.

Did you know

A fully grown Mertens' carpet anemone can spread wider across than a trash can lid, and it is genuinely the largest sea anemone species known, edging out even the magnificent anemone for sheer surface area.

Symbiotic relationships

Clownfish and their host anemones

A clownfish lives inside an anemone that stings and eats other fish its size. Its mucus coat keeps the anemone's stinging cells from firing, and a new fish builds that protection up over hours of brief touches. The fish gets a refuge no predator will follow it into and a nest site at the anemone's base. The anemone gets a guard that drives off the butterflyfish that would graze its tentacles, a steady supply of nitrogen from the fish's waste, and water movement at night, when the fish fans its fins among the tentacles and the anemone takes up more oxygen. Only ten anemone species host clownfish in the wild, and each clownfish species uses its own short list of them.

Captive-bred clownfish have never seen an anemone and do not need one; they settle for a coral, a powerhead or a corner of the tank. If you want the pairing, the anemone is the harder animal by far and goes in first, into a mature tank with strong light and stable water, at the tank size its own profile lists. The bubble tip anemone is the hardy host, and the one most clownfish accept in captivity even when it is not a natural host, so a clownfish profile lists it as the usual tank host where that is the case. The sebae, magnificent and carpet anemones are marked difficult, and the carpets eat fish. Expect a paired clownfish to defend its anemone against everything else in the tank.

Shrimp and crabs that live in anemones

Several small crustaceans live where almost nothing else can: among the tentacles of an anemone. Sexy shrimp perch in the tentacles in a cluster, bobbing their tails in the display that named them. The white-spot anemone shrimp is near transparent apart from its spots and lives on carpet anemones. The porcelain anemone crab sits at the anemone's edge and filters plankton from the water with two fan-like arms. Pederson's cleaner shrimp lives in the Caribbean corkscrew anemone and cleans fish from there. In every case the anemone is a bodyguard: its sting keeps off the small fish that would eat the shrimp. The anemone gains little, and the white-spot shrimp will nibble its host's tentacles when it is hungry.

Give each of them its anemone. Sexy shrimp take a rock flower anemone, a bubble tip or a carpet. The white-spot shrimp and the porcelain crab want a carpet anemone or a long tentacle anemone, both of which need a mature tank at the tank size their profiles list. Pederson's shrimp wants a corkscrew anemone or a condy. Without a host they perch on a coral or hide in the rock and are picked off by any fish that eats shrimp, so they suit a peaceful nano reef. A clownfish will evict them from an anemone it has claimed.

Every symbiotic relationship in the catalog

Common questions

What size tank does a Mertens' carpet anemone need?

A Mertens' carpet anemone needs at least 53 gal (200 L). It spends most of its time in the bottom.

What temperature and pH does a Mertens' carpet anemone need?

A Mertens' carpet anemone is comfortable at 75–81°F (24–27°C) with a pH of 8.1–8.4.

How big does a Mertens' carpet anemone get?

An adult Mertens' carpet anemone reaches about 35.4 in (90 cm).

Related species