Starfish, also known as sea stars, are captivating marine invertebrates found in diverse ocean habitats globally, from shallow intertidal zones to the deep-sea floor. These fascinating creatures, members of the phylum Echinodermata, typically feature a central disc with radiating arms, though the number of arms can vary significantly among species. While they are often observed clinging to rocky substrates or burrowing in sand, starfish occupy a complex position within marine food webs, serving as both predators and prey.
Who Preys on Starfish
Various marine animals prey on starfish. Sea otters (Enhydra lutris) are known to consume starfish, often using their strong paws or rocks to break open their tough bodies.
Certain fish species also target starfish. Triggerfish and pufferfish possess strong jaws and specialized mouthparts to crush the starfish’s calcified skin. Sharks, particularly bottom-dwelling species like nurse sharks and horn sharks, can also prey on starfish. Manta rays, while primarily plankton feeders, may also consume starfish.
Crustaceans such as crabs and lobsters are known predators of starfish. Alaskan king crabs can tear starfish apart with their strong claws. Even other starfish species engage in predation; the morning sun star (Solaster dawsoni) and the sunflower sea star (Pycnopodia helianthoides) actively hunt and consume other sea stars, along with sea urchins, crabs, and snails. Birds like gulls occasionally feed on starfish found in intertidal zones.
How Starfish Protect Themselves
Starfish have evolved a variety of defense mechanisms to deter predators. Their most apparent physical defense is their tough, calcified skin, often covered with spines or bumps. These spines can be sharp and make the starfish unpleasant or difficult to consume for many animals. Some species, such as the crown-of-thorns starfish (Acanthaster planci), possess long, venomous spines that can inflict pain and irritation upon contact.
Beyond physical deterrents, many starfish employ chemical defenses. They can produce unpalatable compounds called saponins in their body walls, which deter predators by making them taste unpleasant. Some species, like the “slime star” (Pteraster tessellatus), can secrete large amounts of repellent mucus when agitated. Certain starfish also contain powerful toxins, such as tetrodotoxin.
Autotomy is the ability of a starfish to intentionally shed an arm when caught by a predator. This allows the starfish to escape while the predator is distracted by the detached limb. Starfish can regenerate lost arms, and some species can even regrow an entire individual from a single arm if a portion of the central disc is present. Passive defenses include camouflage, where their coloration, patterns, and irregular body textures allow them to blend with their surroundings, such as coral reefs or sandy seabeds, making them harder for predators to spot.
The Role of Starfish in Ocean Ecosystems
Starfish are important components of marine ecosystems. They primarily feed on benthic invertebrates such as mollusks, barnacles, and sponges, helping to regulate the populations of these organisms. For example, some starfish species are important predators of mussels, preventing them from overpopulating certain areas and outcompeting other species for resources.
Their feeding activities help maintain the balance and diversity of marine communities. The predation of starfish on sea urchins helps protect kelp forests from overgrazing, allowing these habitats to thrive and support a wide array of marine life.