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What do sea stars eat
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What Do Sea Stars Eat? Clams, Coral and a Stomach That Leaves the Body

Sea stars eat clams, mussels, coral, and rock film. See how they digest prey outside their bodies and what their diet means for tanks and beaches.

Jack·7 min read·June 26, 2021·Updated October 16, 2026

You crouch over a tide pool, spot an orange star wedged against the rock, and wonder what something with no visible face could possibly eat. Most sea stars are predators. Many eat shellfish such as clams and mussels, which they pry open with hundreds of tiny tube feet before pushing their own stomach inside the shell. Diet varies by species, though. The crown-of-thorns starfish eats living coral, and some aquarium favorites graze on rock surfaces. Here is how they eat, what different species prefer, and what that means for a tank or a beach.

First, a sea star isn't a fish

"Starfish" is the common name, but NOAA points out that sea stars have no gills, scales or fins. They are echinoderms, the same group as sea urchins and sea cucumbers. There are nearly 1,900 living species, sorted into 36 families.

Their bodies work very differently from ours. A sea star has no brain and no blood. Seawater moves nutrients around its body through a network called the water vascular system. That same plumbing is what lets it hunt.

How a sea star finds and grips its food

The mouth is on the underside, at the center of the body where the arms meet. Rows of tube feet line the underside of each arm, and the sea star crawls on them.

Water enters through a small sieve-like plate on top called the madreporite. From there it flows through the stone canal and a ring canal into radial canals that run down each arm. These feed small bulbs called ampullae, which give the tube feet their suction. The result is hundreds of small, hydraulically powered grippers.

To find prey, many sea stars rely partly on light-sensitive eyespots at the tips of their arms. These eyespots can't form detailed images, but they sense light and help the animal locate food.

The stomach that goes out to the meal

A clam or mussel clamps its shell shut, so the sea star doesn't try to crack it. Instead, it grips both shell halves with its tube feet and pulls steadily. Eventually the shell gapes, even slightly.

That small gap is enough. The sea star pushes part of its stomach, called the cardiac stomach, out through its mouth and into the shell. There it releases digestive enzymes and starts breaking down the animal inside its own shell.

Digestion happens in two stages. The cardiac stomach does the first part outside the body. The partly digested food then moves to a second stomach, the pyloric stomach, where digestion is finished. Because the first stage happens outside, a sea star doesn't need to swallow its meal whole.

Not every sea star eats clams

The external stomach works on more than shellfish, and different species use it on very different food.

The crown-of-thorns starfish feeds on live coral polyps. It covers the coral, liquefies the polyps with digestive enzymes, and leaves bare white skeleton behind. Outbreaks of this species have caused widespread coral death on the Great Barrier Reef since 1962.

Other species are grazers rather than hunters. The chocolate chip sea star and many others commonly sold for aquariums pick food off rock surfaces, and some species sift through sand. So "sea stars eat mollusks" is only part of the story. What a given star eats depends on its species and where it lives.

Why one sea star's diet can shape a whole shore

On the rocky coast of the Pacific Northwest, the ecologist Robert Paine studied the ochre sea star, Pisaster ochraceus. When he removed it from a stretch of shore, the mussel Mytilus californianus took over and the community became less diverse. That work gave ecology the idea of the keystone species: one predator whose feeding holds a whole community in balance.

This is part of why scientists worry when a large sea star disappears. Since 2013, sea star wasting disease has wiped out about 90% of the Pacific population of the sunflower sea star. The California Ocean Protection Council considers the species functionally extinct in California, and the IUCN lists it as critically endangered.

In 2023, NOAA Fisheries proposed listing the sunflower sea star as threatened under the Endangered Species Act across its range, from Baja California to Alaska. In June 2026, the Center for Biological Diversity sued NOAA, arguing the agency had missed its deadline to issue a final rule. As of early July 2026, no final rule had been issued.

Feeding a sea star in an aquarium

If you're thinking about a sea star for a home tank, diet is the hard part. Starvation is the main long-term risk. One hobby profile of the chocolate chip sea star says its long-term success rate "appears to be poor, as most die of malnutrition." Many grazing species depend on the film of food growing on established live rock. A new or very clean tank may not have enough to keep them alive.

Because diets differ so much, find out exactly which species you have before planning how to feed it. No single tank size fits all sea stars. One reef database suggests about 600 liters (roughly 160 gallons) for Linckia and about 400 liters (roughly 105 gallons) for the sand-sifting Archaster. Treat those numbers as hobbyist guidance, not hard rules.

Sea stars are also very sensitive to changes in water chemistry. Drip acclimation is strongly recommended when adding one to a tank, and a sea star should never be lifted into the air while you handle it.

Before you take one home from the beach

A tide-pool sea star may be legally off-limits.

  • California: State regulations bar taking tidepool invertebrates between the high tide mark and 1,000 feet seaward of the low tide mark, except for a short list of species. Sea stars are not on that list, and a Southern California tidepool guide marks all sea stars "No Take." In state marine reserves, taking any invertebrate is prohibited.
  • Florida: Harvesting the Bahama starfish (Oreaster reticulatus) is banned, both commercially and recreationally, and so is selling it. Collecting any shell with a living animal inside requires a recreational saltwater license, even from shore. Manatee County also limits harvest to two live-containing shells per species per day, and that limit includes starfish.

In most cases, the best way to watch a sea star eat is to leave it in the tide pool. It may take hours, but you could catch it slowly pulling a mussel open.

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