Mottled Star (Evasterias troschelii): The Kelp Forest's Opportunist

Every kelp coast has a sea star that lives in the gap between the famous ones — too soft-bodied for the wave-swept rocks where ochre stars hold court, too small and drab to make posters like the sunflower star. On the northeast Pacific coast that is the mottled star (Evasterias troschelii), also sold to generations of tidepoolers as the false ochre star. It is a flexible, many-mooded predator of the low intertidal and subtidal reef edge, a specialist in snails and limpets, and — less famously — a predator of other sea stars' young. If you dive or shore-walk kelp country from the Aleutians to northern California, this is the star you are most likely to misidentify, and among the most instructive to watch. Here is how to know it, and what it does all day.

Fast facts

Scientific name	Evasterias troschelii (family Asteriidae)
Common names	Mottled star, false ochre star, true star (Canada)
Range	Aleutian Islands and Alaska south to northern California
Habitat	Low intertidal to subtidal, to ~70 m; protected rocks, kelp beds, pilings — avoids violent surf
Size	Commonly 12–20 cm across; big arms-span records near 30 cm
Colour	Enormously variable — grey, buff, rust, orange, violet, often mottled or blotched
Diet	Limpets, snails (including whelks), barnacles, small mussels and clams; also juvenile sea stars, sea urchin young, other asteroids

Knowing the false from the true

The common name says it plainly enough: generations of shore-watchers have logged this animal as an ochre star. Both are five-armed asteriids of kelp-country rock, and at a metre's distance, in poor light, the confusion is honest. Up close, they stop looking alike.

Texture and spines

The ochre star's skin feels like a coarse file, studded with dense, blunt, chalky spines in radiating fans — a star built as armour. The mottled star feels soft and slightly slippery, almost suede-wet, with spines that are longer, sparser and arranged primarily in one lengthwise row down the back of each arm rather than in starburst fans. The disc is smaller relative to the arms, which are more tapered and flexible. Pick an ochre star up (gently, briefly, attended by water) and it holds its shape; the mottled star drapes — a body plan that reads "shelter-dweller," not "surf-fighter."

Habitat is half the identification

Found in the open mid-intertidal on a surf headland? Ochre. Under a rock, in a shaded surge gulley, on a piling below the tide line, or down in the kelp shallows? Strong presumption of mottled star. It shuns both heavy surf and long exposure; its world is the low and the sheltered, including the subtidal reef fringe where it reaches its greatest numbers. In British Columbia and Alaska it is often described by divers as the commonest star on protected rocky bottom.

The colour problem

Where the ochre star offers a tidy purple-or-orange binary, the mottled star nearly refuses to be named: greys and buffs, muted browns, brick-red arms on a grey disc, violet patches, cream mottling. The pattern is literally its name. Learn structure, not paint: velvety feel, tapered arms, single spine rows, low and sheltered habitat — that cluster of characters is the animal.

The generalist's menu

An ochre star is, above all, a mussel specialist. The mottled star is the boreal reef's opportunist, and its diet reads like a roll-call of mid-sized invertebrates:

• Limpets and chitons, levered or humped over;
• Snails, including dogwhelks such as frilled dogwinkles — a predator of a predator;
• Barnacles scraped from their plates, and small mussels and clams;
• Juvenile sea urchins working through young kelp recruits; and
• other sea stars — most notably the soft-bodied young of large asteroids. Small mottled stars eat small stars; large ones have been recorded taking juvenile ochre stars and the youngsters of the sunflower star.

It also scavenges readily. In food-web terms this breadth makes Evasterias a mesopredator: too low-slung and ecologically diffuse to restructure a community the way Pisaster ochraceus does, but a constant drag on the recruitment of snails, limpets, bivalves and echinoderms alike. Where ochre stars enforce one great boundary, mottled stars apply a hundred small taxes.

A slower metabolism of violence

The hunting style matches the build. Unable to clamp against surf, it instead slides into position with a stealth the rigid stars lack, applies the same water-vascular tube feet, and evests its stomach through the usual gap. Divers report it wrapped limpet-like around a whelk for hours, or folded over a barnacle patch in slow sweep-netting arcs. Everything about Evasterias is lower and slower than Pisaster — lower on the shore, lower in profile, slower in movement — and patient.

Predators of predators

The mottled star's flexible life has hard edges above. The morning sun star, the Pacific's specialist hunter of asteroids, pursues it; the great gumboot chiton has no quarrel with it, but the glaucous-winged gulls and sea otters do, and their toll on exposed animals is one reason this star hugs shelter. Its defences are the asteroid standbys — a tough-skinned, hard-to-swallow body; arms autotomised under attack; slow regeneration — plus a habit the ochre star has less need of: knowing when to be nowhere in sight.

Wasting disease and the protected-position story

When sea star wasting syndrome swept the coast in 2013–2014, the mottled star was among the species recorded melting on northern reefs, and observers who knew where to look watched long-familiar aggregations vanish from pilings and kelp-edge boulders. The pattern that emerged echoed its ecology: sheltered, deeper, cooler water buffered the losses compared with warm shallow enclosed sites, and recovery at deeper survey stations outran recovery on exposed shore. A decade on, the species is broadly present again through the north of its range, with the same asterisk hanging over every Pacific star — each new marine heatwave is a test it must pass again. For monitors reading reefs for health, Evasterias is part of the indicator assemblage: not a headline species, but one whose rebound tracks the subtidal community's.

Where to find a mottled star

• Under stable low-intertidal rocks on protected shores — always turned back exactly as they lay;
• on pilings, breakwaters and shaded jetty walls, often in the company of plumose anemones;
• subtidal reef margins and kelp-holdfast boulders from about 5 m down through the core kelp belt — classic territory for BC and Alaska dives such as those in Hakai Passage;
• surge gulleys and overhangs on semi-exposed coasts, where it exploits wave-baffled rock the ochre star has to abandon.

Look for the drape first, the spine row second, the mottled uncertainty of colour last — and you will stop writing "ochre?" in your notebook where the animal has been insisting, all along, on being itself.

Some predators draw the great lines of the shore. The mottled star does the fine print — and a reef is regulated by its fine print as surely as by its boldface.

Key takeaways

• The mottled star (Evasterias troschelii) is a soft-bodied, colour-variable five-armed star of sheltered low-shore and subtidal rock from Alaska to northern California.
• Tell it from the ochre star by suede-soft skin, tapered flexible arms, spines in single lengthwise rows (not radiating fans), and habitat — under rocks, on pilings, below the tide line.
• It is a generalist mesopredator: limpets, whelks, barnacles, small bivalves, young urchins and juvenile sea stars — a constant tax on recruitment across the reef community.
• Wasting disease hit it hard in warm shallow water, but deep sheltered populations buffered losses and it has broadly recovered through the north.
• Find it on protected shores and subtidal kelp-edge boulders; learn it by structure, not colour.

FAQ

Is the mottled star the same as a false ochre star?

Yes — "false ochre star" is the older common name for Evasterias troschelii, earned by its resemblance to the true ochre star (Pisaster ochraceus). Both names refer to the same single species.

How can I be sure I'm not looking at an ochre star?

Use texture and place. Ochre stars have dense, chalky, starburst-arranged spines, a rigid body, and dominate open surf-swept rock. Mottled stars feel soft and slippery, have long tapered arms with lengthwise spine rows, and stick to sheltered, shaded or subtidal habitat.

Do mottled stars really eat other sea stars?

Yes. They take the juveniles of larger asteroids, including young ochre stars and sunflower stars, and will attack smaller asteroids outright. Predation between sea-star species is a normal feature of boreal reef food webs.

Was the mottled star hurt by sea star wasting?

It was — heavily in warm, shallow, enclosed waters from 2013 onward. Losses were lighter at depth and on exposed, cooler coasts, and the species has rebounded through much of its northern range, though the disease persists and flares in warm years.

How deep do mottled stars live?

From the low intertidal down to roughly 70 metres, with their greatest densities in the shallow subtidal kelp belt and on sheltered boulder bottoms.