Starfish, often referred to as sea stars, are captivating marine invertebrates recognized for their unique radial symmetry. These animals belong to the class Asteroidea, part of the larger phylum Echinodermata, which also includes sea urchins and sand dollars. Starfish are found across all the world’s oceans, inhabiting diverse environments from shallow intertidal zones to the deep sea at depths of up to 6,000 meters.
Common Prey and Food Sources
Most starfish species are carnivorous, preying on benthic invertebrates. Their diet includes slow-moving or sessile organisms found on the ocean floor, such as mollusks (clams, mussels, oysters), gastropods (snails), and crustaceans (barnacles, small crabs).
Starfish are opportunistic feeders. Many species also scavenge, consuming detritus like decomposing organic matter, dead organisms, and leftover food particles, which helps maintain aquatic environments. Some species consume fish eggs or other smaller invertebrates.
How Starfish Consume Their Meals
Starfish have a distinctive feeding mechanism, allowing them to consume prey larger than their mouths. They use numerous tube feet on their underside to grip and manipulate prey. Operated by a hydraulic water vascular system, these feet exert a powerful grip, slowly prying open bivalve shells like clams and mussels. A gap of only 0.1 to 0.5 mm is sufficient for the next feeding stage.
Once a small opening is created or the prey is secured, many starfish species evert, or push out, their cardiac stomach through their mouth. This everted stomach then envelops the prey, even if it is still partially within its shell. Digestive enzymes are secreted by the stomach onto the prey, beginning the process of external digestion. The enzymes liquefy the prey’s tissues, allowing the starfish to absorb the digested nutrients through its stomach lining. After digestion is complete, the stomach is retracted back into the starfish’s body, leaving behind any indigestible hard parts.
Specialized Diets and Variations
While many starfish are generalist predators, some species have specialized diets. The Crown-of-Thorns starfish ( Acanthaster planci ), for example, is a predator of hard corals. This species extends its stomach over coral polyps, secreting enzymes to digest the coral tissue and absorbing the resulting “coral soup.” An adult Crown-of-Thorns starfish can consume up to 10 square meters of coral per year.
Other starfish species exhibit different dietary preferences. Some are specialized in consuming sponges, while others are deposit feeders, ingesting organic matter directly from sediments. Filter-feeding starfish capture plankton and suspended particles from the water column, utilizing their tube feet or specialized structures for this purpose. The diversity in feeding strategies highlights the adaptability of starfish to various marine environments and food sources.