Starfish, often called sea stars, are marine invertebrates found in diverse ocean environments. Nearly 2,000 species exist, belonging to the class Asteroidea. This article explores their dietary habits and unique feeding mechanisms.
General Diet of Starfish
Most starfish are opportunistic feeders, acting as both predators and scavengers within their marine habitats. Their diet commonly includes slow-moving or sessile invertebrates like clams, mussels, oysters, snails, and barnacles. Some species also scavenge on detritus, decaying organic matter. This scavenging behavior contributes to nutrient cycling in marine ecosystems.
Unique Feeding Mechanisms
Starfish possess a unique method for consuming their food, particularly larger prey. When a starfish locates prey, such as a bivalve, it positions itself over the organism. The starfish then uses its tube feet, which are hydraulic appendages, to firmly grip the prey and exert a pulling force on its shells. This continuous pressure tires the bivalve’s adductor muscles, causing its shells to open.
Once a small opening is created, the starfish performs stomach eversion. It pushes its cardiac stomach out through its mouth and directly onto or into the prey. This everted stomach then releases digestive enzymes, beginning the external digestion of the prey’s soft tissues. The partially digested, liquefied material is absorbed by the stomach lining and drawn back into the starfish’s body for further digestion. This unique adaptation allows starfish to consume prey much larger than their small oral opening would otherwise permit.
Diverse Diets Across Species
While many starfish are generalist predators, their diets can vary significantly among different species, reflecting specialized adaptations and ecological roles. The Crown-of-Thorns starfish ( Acanthaster planci ), for instance, is a well-known predator of hard coral polyps. These starfish can consume up to 10 square meters of coral per year, posing a significant threat to coral reefs during outbreaks.
The Sunflower Sea Star ( Pycnopodia helianthoides ) is another specialized predator, primarily feasting on sea urchins, which can constitute a large portion of its diet, sometimes ranging from 21% to 98%. They also consume crabs, snails, clams, and even other sea stars.
Some starfish species are primarily detritivores, feeding on decomposing organic matter and fecal material found on the seafloor. Others are suspension feeders, capturing phytoplankton and other microscopic particles drifting in the water column. Certain starfish, such as species of Henricia and Echinaster, are known to feed on sponges, while some, like the Chocolate Chip Star and certain Fromia species, incorporate algae into their diet.