The Crown-of-Thorns Starfish (CoTS), scientifically classified as Acanthaster species, is a large marine invertebrate found throughout the Indo-Pacific region. It is recognizable by its disk-shaped body and long, venomous, thorn-like spines, which give the creature its name. The CoTS is a predator of significant concern on tropical coral reefs due to its immense appetite. Its diet centers almost entirely on living coral tissue, establishing it as a major consumer in the reef ecosystem.
Coral: The Primary Food Source
The adult Crown-of-Thorns Starfish feeds on the living tissue of hard, stony corals (Scleractinia order). These animals are corallivorous, preying on the soft polyps that build the reef’s calcium carbonate structure. The starfish exhibits a clear preference hierarchy for certain coral species when feeding.
It strongly favors fast-growing, branching and tabular corals, such as those belonging to the Acropora and Pocillopora genera. Their consumption leads to a rapid loss of three-dimensional habitat complexity. After the starfish digests the living tissue, it moves on, leaving behind a stark, white patch of coral skeleton. An individual adult CoTS can consume up to 12 square meters of coral tissue annually.
The Unique Feeding Mechanism
The CoTS consumes coral using stomach eversion. The starfish does not chew or swallow its prey whole. Instead, it climbs onto the coral and pushes its stomach out through its central mouth, draping the soft organ over the coral’s surface.
Once everted, the stomach secretes digestive enzymes directly onto the coral tissue. This external digestion breaks down the coral polyps and the organic matter they contain. The CoTS then absorbs the resulting liquefied slurry back into its body, retracting its stomach once the meal is complete. This unique method allows the starfish to feed without ingesting the hard, calcareous skeleton.
When Coral is Scarce: Alternative Diets
While adult CoTS rely heavily on hard coral, their diet is flexible when preferred food sources are scarce. This flexibility is most pronounced during early life stages. Newly settled juveniles begin life as herbivores, initially feeding on crustose coralline algae (CCA), a calcium-based algae common in reef environments.
If hard coral is unavailable, adults may switch to secondary food sources, including soft corals, sponges, and other encrusting sessile invertebrates. This dietary shift is less efficient for growth and reproduction. Juvenile CoTS can remain in a prolonged herbivorous phase, subsisting on low-energy food like biofilm for months or years, delaying their transition to the adult stage until conditions improve.
The Ecological Impact of CoTS Feeding
The feeding habits of the CoTS significantly impact the structure and health of the reef ecosystem. When populations are at normal levels, they help maintain diversity by selectively preying on fast-growing corals, preventing these species from dominating the reef. However, when populations explode in “outbreak cycles,” their high consumption rates cause widespread devastation.
These outbreaks can result in the rapid destruction of up to 90% of live coral cover, transforming complex habitats into barren rubble fields. The loss of reef-building corals reduces biodiversity, as associated fish and invertebrate species lose shelter and food sources. Extensive coral mortality can trigger a “phase shift,” where the reef becomes overrun by algae and sponges, hindering long-term recovery. Outbreaks are often exacerbated by environmental factors, such as increased nutrient runoff and the overfishing of natural predators.