Starfish are marine invertebrates found in various ocean environments. While they appear to move slowly, many species are active predators with effective hunting abilities. They play a significant role in their ecosystems, with diverse feeding behaviors.
The Predatory Nature of Starfish
Many starfish species are predators, consuming other marine organisms. Their diet commonly includes bivalves like clams, mussels, and oysters. Starfish also prey on barnacles, snails, and other echinoderms such as sea urchins and other starfish species. For example, the common sea star, Asterias rubens, primarily feeds on mussels and oysters.
While many starfish are predators, not all species share this hunting lifestyle. Some are scavengers, feeding on dead organic matter or detritus. Other species are filter feeders, capturing microscopic particles and plankton from the water column. This diversity highlights the varied adaptations within the starfish group.
Unique Hunting and Feeding Strategies
Starfish employ unique methods to capture and consume prey. They use hundreds of suction-cupped tube feet for both locomotion and grasping prey. When attacking a bivalve, a starfish positions itself over the shell and uses its tube feet to exert a steady, powerful pull. This continuous force, though slow, eventually fatigues the bivalve’s adductor muscles, causing the shell to gape open slightly.
Once an opening is created, the starfish uses stomach eversion. It pushes its stomach out through its mouth and inserts it into the prey’s shell. Digestive enzymes are then released directly into the bivalve, breaking down its soft tissues. After the prey’s body is liquefied, the starfish retracts its stomach, absorbing the digested meal.
Ecological Role as Predators
Starfish play a significant role in maintaining the balance of marine ecosystems. They can greatly influence the distribution and abundance of other species, preventing single species from dominating a habitat. This regulatory function is especially evident in their impact on sessile organisms like mussels and barnacles.
An example of their ecological importance is the ochre sea star, Pisaster ochraceus, found along the Pacific coast of North America. This species is considered a “keystone species,” meaning its presence has a disproportionately large effect on its environment relative to its abundance. Pisaster ochraceus preys on mussels, preventing them from monopolizing space on rocky shores. Without this predation, mussel beds would outcompete other organisms, leading to a decrease in biodiversity.