The Bizarre Truth: 5 Shocking Foods Starfish Eat (And How Their Stomach Does The Impossible)

The ocean floor is a silent battlefield, and the starfish—or sea star—is one of its most fascinating and effective predators. Far from being a gentle, decorative creature, this echinoderm employs a bizarre and shocking feeding mechanism to consume prey that would seem impossible for an animal without jaws or teeth. As of the current date in December 2025, the latest research continues to highlight their critical role as keystone predators, shaping entire marine ecosystems through their voracious and varied appetites.

The diet of a sea star is incredibly diverse, ranging from slow-moving mollusks to fast-growing coral reefs. Their feeding habits are not just about survival; they are fundamental to maintaining the health and balance of intertidal and subtidal communities worldwide. Understanding "what do starfish eat" requires a deep dive into their anatomy and the specific ecological niche occupied by different species.

The Starfish Diet: A List of Primary Prey and Scavenged Foods

Sea stars are classified primarily as carnivores and scavengers, though some species are omnivorous, consuming both plant and animal matter. Their slow movement dictates a diet of equally slow or sessile (attached) organisms. The sheer variety of their food sources is a testament to their adaptability in the marine environment.

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1. Bivalves and Gastropods (The Staple Diet)

The most famous and critical part of the starfish diet consists of hard-shelled mollusks. These are the primary food sources for many common species and include:

• Mussels: Species like the Ochre Sea Star (*Pisaster ochraceus*) are renowned for preying on mussel beds, a behavior that earns them the title of "keystone predator." By controlling the mussel population, they prevent one species from dominating the rocky shore ecosystem.
• Clams and Oysters: Sea stars are a major threat to commercial oyster and clam beds, using their powerful tube feet to slowly pry open the shells.
• Snails and Limpets: Various species of sea stars also consume smaller gastropods and limpets that cling to rocks.
• Barnacles and Chitons: These sessile invertebrates are also easy targets for a hungry sea star.

2. Other Echinoderms and Invertebrates (The Cannibalistic Menu)

The starfish diet is not limited to mollusks. They are known to consume their own relatives and other spiny-skinned creatures:

• Sea Urchins and Sand Dollars: The Sunflower Sea Star is particularly famous for its appetite for sea urchins. In kelp forests, the decline of the Sunflower Sea Star due to factors like Sea Star Wasting Disease has led to an explosion in sea urchin populations, creating "urchin barrens" that destroy kelp forests.
• Crabs and Shrimp: Smaller crustaceans are a common meal, often scavenged or hunted if they are slow enough.
• Other Sea Stars: Cannibalism is not unheard of. Some large, predatory sea stars will consume smaller or weaker members of their own kind or other species.

3. Coral Polyps (The Reef Destroyer)

One of the most ecologically significant and damaging diets belongs to the Crown-of-Thorns Starfish (*Acanthaster planci* or COTS). This species is a specialized corallivore:

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• Hard Corals: The COTS feeds almost exclusively on the soft tissue of hard, stony coral polyps, including genera like *Acropora*, *Pocillopora*, *Pavona*, and *Porites*.
• Ecological Impact: An adult COTS can consume up to 10 square meters of coral a year. Outbreaks of this species are a major cause of coral reef degradation, particularly on the Great Barrier Reef, highlighting the devastating impact a specialized starfish diet can have on an entire ecosystem.

4. Detritus and Organic Matter (The Scavengers)

Many sea stars, especially those in sandy or muddy habitats, function as critical ocean floor scavengers. They play a vital role in cleaning up the seabed:

• Detritus: They consume decaying organic matter, including dead fish, plant material, and fragments of other organisms.
• Bacteria and Algae: Omnivorous species will also graze on films of bacteria and algae that coat rocks and sand.
• Plankton: The larvae of sea stars feed on phytoplankton and zooplankton, and some adult species may also filter-feed on these microscopic organisms.

The Bizarre Anatomy: How Starfish Eat Without a Mouth

The question of "how do starfish eat" is perhaps more compelling than what they eat. Unlike most animals, the vast majority of sea stars do not chew their food. Instead, they have evolved a truly unique and somewhat grotesque feeding strategy known as stomach eversion.

This process allows them to digest their prey externally, overcoming the limitation of their tiny mouth located on the underside of their central disc. This is the secret to how a slow-moving, shell-less creature can consume heavily armored prey like mussels and clams.

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The Two-Step Eversion Mechanism

The feeding process is a marvel of invertebrate biology, relying heavily on their hydraulic system and specialized organs:

1. Prying Open the Prey: A sea star first secures its prey—such as a clam—using hundreds of tiny, muscular tube feet on its arms. These tube feet operate using a water vascular system, generating immense suction power. The sea star pulls the bivalve's shells apart just enough to create a minuscule gap—sometimes as little as 0.1 millimeters.
2. External Digestion: Once the gap is created, the sea star performs the shocking act of stomach eversion. It pushes its cardiac stomach out of its mouth and into the prey's shell. The stomach then wraps around the soft tissue inside. Digestive enzymes are secreted directly onto the prey, turning the soft body into a liquid or slurry. The sea star then retracts its stomach, along with the pre-digested meal, back into its body.

This ability to digest food outside the body means a sea star can consume prey much larger than its own mouth. It's a highly efficient and energy-saving method, especially when dealing with tough, hard-shelled organisms.

Specialized Feeders: Starfish as Ecological Engineers

The diet of a starfish is more than just a list of consumed items; it determines their role in the ocean's complex food web. Different species have specialized diets that make them critical "ecological engineers" in their respective habitats.

The Role of the Ochre Sea Star (*Pisaster ochraceus*)

The Ochre Sea Star, common along the Pacific coast of North America, is the textbook example of a keystone predator. Its preferred food is the California mussel. If the Ochre Sea Star is removed from a rocky intertidal zone, the mussel population explodes, outcompeting and eliminating dozens of other species of algae and invertebrates. The sea star's predatory diet is what maintains the high biodiversity of the entire community.

The Impact of the Crown-of-Thorns Starfish (*Acanthaster planci*)

Conversely, the Crown-of-Thorns Starfish demonstrates how a specialized diet can be detrimental when populations are unbalanced. While a few COTS are a natural part of a coral reef ecosystem, large, unchecked outbreaks can lead to mass consumption of hard corals, fundamentally altering the reef structure and function. The ongoing management of these outbreaks is a major focus of marine conservation efforts across the Indo-Pacific.

Starfish in the Home Aquarium

For those interested in keeping sea stars in a home aquarium, their diet remains crucial, but the specific needs vary greatly by species. Sand-sifting starfish (like the *Archaster typicus*) primarily feed on detritus, tiny organisms, and organic films within the sand bed. Other species, such as the Red Fromia Starfish, are known to graze on sponges and algae. It is vital for aquarists to research the precise dietary needs of their chosen species, as many common sea stars are difficult to sustain long-term without a constant and abundant supply of their natural prey. Their unique feeding habits necessitate a well-established tank environment rich in the microscopic organisms and detritus they rely on for survival.