Strawberry anemone Corynactis californica: the cloning corallimorph that carpets kelp forest reefs — how it feeds, clones and spreads.
The strawberry anemone (Corynactis californica) is a thumb-nail-sized pink polyp that reproduces by tearing itself in half, and does it so relentlessly that entire rock faces in the kelp forests of California end up upholstered in thousands of genetically identical clones. It is one of the most photographed animals on the Pacific reef — the "strawberry patch" that turns grey granite into a candy-pink carpet — and one of the most mislabelled, because despite its name it is not a true sea anemone at all.
It belongs to the corallimorphs, an odd, ancient order of cnidarians that sit between the anemones and the stony corals. That distinction matters: it explains nearly everything strange about the animal, from its clubbed tentacles to the way a single polyp becomes a colony.
Corallimorpharia is a small order — a few hundred species worldwide — of solitary-to-colonial polyps that look like anemones, lack skeletons like anemones, and yet share key features of their internal anatomy and tentacle batteries with stony corals. You can think of them as corals that never learned to build rock, or anemones that kept coral habits.
The strawberry anemone is the group's Pacific-coast celebrity. Each polyp stands one to two centimetres tall, a neat pink-red column crowned by a ring of short tentacles, each ending in a swollen, pale-knobbed tip — the "clubs" that give the species its other common name, the club-tipped anemone. Those knobs are ammunition depots, packed with nematocysts, the microscopic harpoons that all cnidarians use to sting prey.
Compare it to its neighbours and the oddness shows: the giant green anemone is solar-powered by symbiotic algae and hunts big prey with a wide oral disc; the strawberry polyp carries no symbionts at all, lives off drifting plankton, and never stands alone for long.
A strawberry anemone colony begins with a single settled larva. The founding polyp feeds, grows and then splits — a process called longitudinal fission, in which the animal literally tears down the middle from mouth to foot, each half regenerating the organs it is missing. Repeat weekly for a few years and you have a mat: hundreds to thousands of clones packed shoulder to shoulder, every one of them genetically identical to the founder.
The mats have architecture. Polyps along the edges face out into the current; interior polyps crowd for space. Where a mat meets a genetically different clone — a stranger colony that settled nearby — the boundary stays crisp and sometimes combative, with polyps along the frontier stinging rivals into retreat. Where it meets its own flesh, resources share freely.
From the reef's point of view the result is a living shag-pile in shades from soft rose to screaming magenta, most spectacular on the overhangs, pinnacles and shadowed walls of Southern California, where a single boulder face can hold multiple clone-lines laid over each other like quilts.
Every polyp in the mat is a net unto itself. With tentacles spread — most dramatically at night or in a running current — each knobbed crown sieves the water for copepods, larval crustaceans and other zooplankton, as well as edible scraps of kelp-borne detritus drifting through the surge. The sheer density of polyps means a mature carpet extracts a meaningful tax on the plankton flowing over a reef, which is one reason these mats favour current-swept walls and headlands: the food comes to them.
Cloning builds the local empire, but it cannot found a new one across the bay — for that the species uses old-fashioned sex. Mature polyps release eggs and sperm, and fertilised larvae join the plankton before settling on fresh rock elsewhere. This dual strategy is the corallimorph signature: asexual fission dominates space at home, sexual reproduction exports the genotype.
It also makes strawberry anemone carpets interesting objects for the science of larval dispersal. Genetic studies of the broader corallimorph and anemone lineages have shown how coastlines sort drifting larvae according to currents and temperature; Corynactis mats, with each colony wearing a single genotype like a uniform, let researchers literally see those patterns at a glance. Two neighbouring carpets of subtly different hue are often two different clone-lines — the reef keeping its genealogy in paint.
Not much, and that is part of the success story. Fish generally avoid the mats, and most scavengers cannot handle the nematocyst batteries. The specialist exception is the leather star, a soft-skinned, garlic-scented sea star that grazes anemones and corallimorphs with apparent relish, working across a strawberry patch like a slow combine harvester. Some nudibranchs nip at the edges as well. Urchins bulldoze the mats incidentally when barrens advance across a reef — one of the subtler losses when kelp falls and the barrens takeover.
The strawberry anemone ranges from British Columbia to Baja California, but abundance is uneven. It is a creature of the subtidal — from just below the low-tide line on shaded faces down to 30 metres and beyond — and it thickens dramatically toward Southern California and the Channel Islands, where current-fed pinnacles wear it like wallpaper. The classic encounter is a vertical or overhanging wall, kelp thinning overhead, and a swath of pink so dense the rock beneath is rumour.
For divers, it is gateway macro photography: polyps hold still, crown flaring in the strobe, and composition is a matter of finding clean clone-lines against contrasting hydrocoral or encrusting sponge. Fans of kelp cathedral dives such as those around Catalina Island know the species well — the pink bands on shaded rock at depth are often Corynactis.
A few field manners worth keeping: never touch. The mats are delicate, and while the sting is trivial to human skin at worst mildly sticky, careless fin kicks shear polyps off by the dozen. The colonies recover — cloning is what they do — but a kicked bald patch can take seasons to re-upholster.
For reef ecologists, Corynactis is cover with meaning. A healthy, spreading carpet tells you a wall gets consistent current, clean water and zooplankton flux, and that urchin fronts and sediment smothering haven't reached it. In the layered zoning of the subtidal — described in our guide to subtidal zonation — corallimorph mats occupy the low-light middle bands where kelp above has filtered the sun and the surge still feeds. When monitoring divers log the fraction of rock wearing strawberry pink, they are indirectly logging the physics of the site.
That is the deeper charm of the animal: it is both ornament and instrument. The reef's gaudiest carpet is also one of its most legible status reports — soft bodies doing hard accounting on light, food and flow.
Not taxonomically. It is a corallimorph — order Corallimorpharia — a group anatomically closer to stony corals despite having no skeleton. The common name persists because it looks and behaves like a small colonial anemone, but "club-tipped anemone" or "strawberry corallimorph" is more precise.
Only trivially. The nematocysts are scaled for plankton-sized prey; at most you might feel a slight stickiness if you brush a dense mat with bare skin. The real reason not to touch is to protect the colony, which is easily torn by gloves and fins.
Colour varies with clone-line genetics and local conditions. Each uniform patch of colour is typically a single clone — one founder's descendants — so neighbouring patches of different hues are different genetic lineages sharing the same wall.
Under good current and feeding, a polyp may divide on a timescale of weeks, and a mat can visibly expand within a season. Recovery after storm or urchin damage takes longer — seasons to years — because new polyps must fission outward from surviving edges.
Indirectly. They favour the shaded, current-fed bands beneath and beside kelp canopies, and they intercept detritus shedding off the kelp. The canopies also moderate light and surge in ways that suit the mats — one more thread in the reef's tightly woven economy.
The leather star (Dermasterias imbricata) is a smooth, slippery, garlic-scented sea star that hunts anemones and sea cucumbers — biology, range and how to find it.
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