Some starfish consume coral, but this feeding behavior is not universal across all starfish species. Starfish are marine invertebrates, and their diets vary widely, with many species acting as generalist predators within their marine environments.
The Crown-of-Thorns Starfish
The Crown-of-Thorns Starfish (Acanthaster planci) is a prominent coral-eating species. It is one of the largest starfish in the world, capable of reaching up to one meter in diameter. This starfish earns its name from the numerous venomous, thorn-like spines covering its upper surface. Unlike most starfish that have five arms, the Crown-of-Thorns Starfish typically possesses multiple arms, often ranging from 10 to 20.
This species is native to the Indo-Pacific region, inhabiting coral reefs from the Red Sea to the Pacific Ocean, including the Great Barrier Reef. It is a significant predator of stony corals. When its populations are at balanced levels, this starfish plays a natural role in the ecosystem by preying on faster-growing coral species, which can promote coral diversity.
How Starfish Devour Coral
Coral-eating starfish employ a distinct feeding mechanism. They extrude their cardiac stomach through their mouth, located on their underside, directly over the coral polyps. Once everted, digestive enzymes are secreted onto the coral tissue, breaking down its soft tissues externally, effectively liquefying them.
The starfish then absorbs the resulting liquefied coral material into its body, after which the stomach is retracted. This process leaves behind a distinct white coral skeleton, marking the area where the coral tissue has been consumed. An adult Crown-of-Thorns Starfish can consume a substantial amount of coral, with estimates suggesting up to 10 square meters of coral per year.
Impact on Coral Reefs
Outbreaks of Crown-of-Thorns Starfish can severely damage coral reefs. When these starfish occur in high densities, defined as 15 or more individuals per hectare, they can strip a reef of up to 90% of its living coral tissue. Such widespread coral loss leads to a reduction in overall reef habitat and can significantly decrease species diversity within the ecosystem.
The effects extend beyond direct coral consumption, leading to cascading impacts throughout the reef. These include an increase in benthic algae and a decline in the populations of other marine life that depend on healthy coral, such as fish and invertebrates. While Crown-of-Thorns Starfish outbreaks are a natural part of reef ecosystems, their frequency and intensity can be exacerbated by human activities. Factors contributing to more severe outbreaks include increased nutrient runoff, which boosts the food supply for starfish larvae, and the overfishing of natural predators that typically keep starfish populations in check. Although affected reefs can recover over time, the increasing frequency of disturbances, such as marine heatwaves and coral bleaching events, reduces the time available for reefs to regenerate.