Starfish, or sea stars, are marine invertebrates belonging to the phylum Echinodermata, found in every ocean from tropical reefs to polar waters. They play a significant ecological role, with some species, like the ochre sea star, acting as keystone species that regulate community structure in intertidal zones. While their tough, spiny skin and remarkable ability to regenerate lost limbs suggest they are well-protected, sea stars are prey for a range of specialized marine animals. These predators have evolved sophisticated methods to circumvent the sea star’s natural defenses.
Apex Predators of Adult Sea Stars
Several specialized hunters target adult sea stars as a primary food source in marine ecosystems. Among the most effective are predatory fish found on coral reefs. Triggerfish, such as the titan triggerfish, and various pufferfish are known to actively consume sea stars. These bony fish possess powerful jaws and specialized dentition for crushing the hard, calcified bodies of their prey. Specialized mollusks also pose a significant threat, particularly the giant triton, or Triton’s Trumpet snail (Charonia tritonis). This massive gastropod is a predator of the Crown-of-Thorns starfish (Acanthaster planci). The triton snail can reach lengths up to two feet, making it a formidable foe for even the largest sea stars.
On the Pacific coast, marine mammals like the sea otter occasionally include sea stars in their diet. While sea otters more commonly prey on sea urchins and bivalves, they will consume species like the sunflower sea star. Seabirds, particularly gulls, attack sea stars exposed in the intertidal zone during low tide. Invertebrate predators, including crabs and lobsters, also contribute, with the red king crab using its strong claws to break apart the sea star’s calcium carbonate skeleton.
Overcoming Defenses: How Predators Consume Starfish
A sea star’s defense is its tough outer layer, composed of interlocking calcium carbonate plates called ossicles, often covered in spines and chemically defended with saponins. Predators must possess specific adaptations to bypass this formidable armor. The pufferfish and triggerfish utilize their beak-like jaws and fused teeth. These powerful oral structures allow the fish to crush the skeletal plates of the sea star, exposing the soft internal tissues.
The giant triton snail employs a combination of chemical and mechanical tactics to subdue its prey. It tracks sea stars using a keen sense of smell, following the scent trails left by its target. Once it catches the sea star, the triton injects a paralyzing agent through its saliva, which quickly immobilizes the victim. The triton then uses its radula, a structure lined with thousands of rasping teeth, to tear through the sea star’s spiny skin. It inserts a long proboscis into the body, consuming the tissue piece by piece. This specialized feeding method allows the triton to consume even the toxic Crown-of-Thorns starfish, a toxin to which the snail has developed a tolerance.
Other invertebrates, such as predatory crabs, use force to overcome the sea star’s defense. They often target the joints between the arms or the central disc, using their chelipeds, or claws, to snip off limbs or crack open the body. The sea star may trigger autotomy, shedding an arm to escape, but the predator still gains a meal in the severed limb.
Vulnerable Stages: Predation on Larvae and Juveniles
Larval Predation
Mortality for sea stars occurs during their earliest life stages, long before they develop the defenses of the adult form. Sea stars begin as planktonic larvae that drift in the water column for weeks to months. In this stage, they are consumed by predators, including filter feeders like clams and sea squirts, as well as planktivorous fish that strain the water for food.
Juvenile Predation
Once the larvae settle and metamorphose into juveniles, they face predators in the benthic environment. Small benthic invertebrates, such as crabs, shrimp, and polychaete worms, prey on these newly settled individuals. These small predators can consume the millimeter-sized juveniles before they have a chance to grow and develop their protective spines and ossicles. The chemical defenses present in the larvae and juveniles are not universally effective against all predator types.