Plumose Anemone (Metridium): Species Profile

Where the water runs cold and full of food, the rock grows white trees. Descend below the kelp line in British Columbia, southeast Alaska, Norway or the far south of Chile, and entire walls can disappear under plumose anemones: columns the colour of bone or apricot, up to waist-high, each crowned with a ruff of tentacles so finely branched it looks like ostrich plume. When a current runs, the crowns wave. When slack comes, they hang like heavy lace. A mature plumose bed is one of the great underwater spectacles of the temperate seas — and it is built entirely by animals that never move faster than a slow creep.

The family name Metridium covers a small cast of look-alike species. On the northeast Pacific coast the dominant one is the giant plumose anemone (Metridium farcimen); in the Atlantic and parts of the Pacific its smaller, ruffled cousin M. senile, the frilled anemone, fills the same role. Between them they write white cursive across the cold reefs of both hemispheres. Alongside gaudier cousins like the giant green anemone of the surf zone and the cloning strawberry anemone, the plumose plays the tower-builder: the deep-flow specialist.

Fast facts

Scientific names	Metridium farcimen (giant plumose, NE Pacific); M. senile (frilled anemone, Atlantic & Pacific)
Group	Class Anthozoa — the flower animals; relatives of corals and other anemones
Range	Cold-temperate and boreal coasts of the North Pacific and North Atlantic, south to southern Chile in similar form
Depth	Shallow subtidal to hundreds of metres; common from about 5–40 m in cold water
Size	M. farcimen columns commonly 15–30 cm; exceptional towers push toward a metre. M. senile rarely exceeds 15 cm
Feeding	Suspension feeding on zooplankton and fine particles via thousands of small tentacles
Reproduction	Sexual spawning plus cloning by pedal laceration — splitting off tissue fragments that grow into new anemones
Lifespan	Likely decades for large individuals

Anatomy of a tower

A plumose anemone is less a flower than a fountain made of meat. The design starts with three parts:

• The column. A smooth, muscular, slightly sticky tube, usually taller than wide, anchored downwards by an adhesive basal disc. Unlike many anemones, Metridium columns are bare — no attached shell fragments or gravel — and often tall with a gentle waist, swaying with the surge like a sapling. Farcimen, the giant, can lift its crown knee-high off the rock, keeping it in faster, cleaner flow.
• The crown. A lobed oral disc fringed with tentacles in dense tiers. In the plumose these tentacles are short, slender and packed by the thousand, creating the feathery, cauliflower-head texture. The mouth sits at the centre, a slit that opens wide enough to take stranded jellyfish and small fish whole.
• The arsenal. Like every anemone, the tentacles bristle with nematocysts — spring-loaded harpoons fine-tuned for plankton-sized prey. Against a human, the effect is mostly invisible: the nematocysts of Metridium are tiny, and touching a crown feels like touching stippled gelatin.

Colour runs from pure white through cream to deep burnt orange, with colour often patchy at colony level: some walls are a single burnished orange, others mixed like weathered marble. The lobing of the oral disc, more elaborate in senile, earns that species the "frilled anemone" name.

Building white forests: cloning and sharing space

Metridium's true distinction isn't the tower; it's the town-planning. Individual plumose anemones multiply faster by walking off copies of themselves than by raising planktonic larvae: small patches of tissue tear away from the spreading basal disc as the animal creeps (pedal laceration), and each fragment heals and grows into a genetically identical clone. Where conditions suit, one founding strain becomes dozens of columns sharing one genome, standing shoulder to shoulder on the same rock.

The result is the spectacular clonal carpet: whole boulders, hull sides and piling wraps converted into a single-colour orchard of swaying crowns. Colonies of one clone hold one shade — white, apricot or amber — so a mixed wall in places like the British Columbia passes or Scottish sea lochs is a map of founder strains that settled and multiplied where the flow was best.

That aggression toward space has rules, though. Where different clones meet, neighbouring anemones can joust with specialised stinging, slugging it out over centimetres with acrorhagi — marginal fighting batteries — much as their relative the giant green anemone defends its tidepool turf. Spatial economies built on stinging: ecology doesn't get much simpler or older.

The filter that runs on plankton

Plumose anemones earn their bulk by running one of the highest-throughput filter-feeding operations on the reef. A spread crown strains copepods, mysids, crab and mollusc larvae, arrow worms and even semi-drowned jelly pus from passing water. Current is everything: the animal preferentially settles on sills, ledges and headland walls where flow delivers food without smothering sediment. Low-flow plumoses close down, retract into sorry-looking white mounds, and wait.

This is why the same physics that drives kelp productivity drives the plumose belt. Strong tidal flushing and seasonal upwelling keep plankton rich and the crowns fed; in slack, sediment-laden backwaters they dwindle. Watch a plumose wall at max tidal flow and you are watching the reef's water column mined in real time — the living bridge between open water and benthic biomass that benthic-pelagic coupling describes.

Fireworks happen too. Disturbed, a plumose can eject threads called acontia through mouth and body wall — white, stinging cords that drift toward whatever bit it. And when prey is caught, tentacles curl inward in a smooth bloom of motion, channelling food toward the mouth. Night divers occasionally catch them ingesting small fish: a sanddab or juvenile rockfish that blundered into the crown gets folded in entirely.

Neighbours, hangers-on and predators

A plumose bed is infrastructure. The lower, shaded columns host candy-stripe shrimps and squat lobsters; shells of giant barnacles and tube worms pack between stalks; and the bed's top edge is patrolled by creatures that eat anemones. The chief predator is the leather star (Dermasterias imbricata), which slides over the columns consuming crowns methodically — divers follow its soft grey hide through half-shorn groves the way you'd find a lawnmower in a field. Nudibranch relatives of Aeolidia also take plumose crowns, and in turn get relieved of the stinging cells they steal: nothing on the reef stays owned for long.

The other way plumose anemones matter is structural. Wreck, piling, pipeline — they are among the first large colonists and among the last to let go, transforming scrap into counted reef. Deepwater trawling, by contrast, strips them wholesale: a single pass can mow a colony that took decades to clone.

Where to see them

Plumose anemones reward cold-water divers everywhere over about 8°C mean water:

• British Columbia and southeast Alaska. Whytecliff, Browning Pass and the passes between the Northern Gulf Islands hold cathedral groves — the Whytecliff wall is a classic beginner encounter.
• Washington and Puget Sound. Current-scoured sills off Deception Pass and the central Sound's deeper walls, where oranges and whites stack in layers.
• Northern Europe. Scottish sea lochs such as Loch Carron, Norway's mid-coast, and the Isles of Scilly all hold dense beds.
• From the surface. Docks, jetties and low-tide bouldery lanes in cold bays publicize them without a tank.

Photograph them with ambient backlight (strobe a touch off-axis) and the crowns glow like chandeliers. Touch nothing: a retracted plumose is a bruise that took weeks to build.

Key takeaways

• Plumose anemones (Metridium spp.) are tall, feathery suspension feeders of cold-temperate reefs; M. farcimen towers higher than any other Pacific anemone.
• They clone by pedal laceration, carpeting rock in single-genome orchards whose colour patches map founder strains — and neighbours fight with stinging acrorhagi.
• Flow is their life: strong tidal currents and upwelled plankton keep the crowns fed; sediment smothers them.
• They convert water-column plankton into reef biomass, host shrimps and squat lobsters, and feed leather stars and nudibranchs in turn.
• Best seen in cold passes, lochs and deeper walls — look but don't touch; these are long-lived, slow-grown animals.

FAQ

Are plumose anemones dangerous to touch?

Their nematocysts are tuned for prey smaller than fingertip skin. Most people feel nothing or a faint tackiness, but gloves are wise, and the real issue is reverse: a grab collapses the crown and wounds the anemone. Observe, don't squeeze.

How do plumose anemones reproduce?

Two ways: sexually, by broadcasting eggs and sperm into the water column, and asexually, by pedal laceration — shedding small tissue fragments from the walking basal disc that grow into genetically identical clones. The clonal carpets you see on cold-water walls are often one animal copied dozens of times.

How big do they get?

The northeast Pacific giant plumose (M. farcimen) commonly stands 15–30 cm tall, and exceptional columns on deep walls approach a metre. The Atlantic frilled anemone (M. senile) rarely tops 15 cm but forms far denser, ruffled aggregations.

What eats a plumose anemone?

Chiefly the leather star (Dermasterias imbricata), which grazes whole groves, and certain large aeolid nudibranchs. Disturbed plumoses fire stinging acontia threads in defence — effective against the slow.

Do plumose anemones move?

They creep, millimetres at a time, by gliding on the basal disc, and can detach and drift briefly to resettle. Mostly, though, a plumose tower is a fixed address held for years — possibly decades — in the one spot the current chose.