The crown-of-thorns starfish is a coral-devouring predator with a complex, venomous defense system.

Nature · Published 30 September 2026 Swipe more like this →

In short: This large, multi-armed starfish uses a unique feeding method: it extrudes its stomach directly over coral to liquefy and absorb tissue. Covered in sharp, venomous spines, it is a formidable presence on reefs, capable of causing significant ecological shifts when its population densities spike across the Indo-Pacific region.

The crown-of-thorns starfish (Acanthaster planci) is a specialized corallivore that thrives across the Indo-Pacific. Unlike typical five-armed starfish, these creatures possess multiple arms—up to 21—and a flexible, disc-shaped body that allows them to navigate the complex contours of branching corals. Their feeding mechanism is remarkably efficient; they climb onto coral colonies using tube feet and evert their stomachs to digest coral polyps externally, leaving behind white skeletal scars that are quickly colonized by algae.

Their defense strategy is both mechanical and chemical. The starfish is covered in stiff, sharp spines that can pierce human skin, causing intense pain, swelling, and bleeding. These spines contain saponins, which act as a chemical deterrent. While some generalist predators, such as the Triton's trumpet snail or certain pufferfish, occasionally consume them, the starfish's defenses make it an unattractive target for most reef inhabitants. This resilience, combined with high fecundity—a 400-mm female can produce up to 53 million eggs—allows populations to potentially surge, leading to significant loss of reef habitat and biodiversity.

The taxonomy and evolutionary history of the genus remain subjects of scientific debate. While some molecular studies suggest the existence of four distinct cryptic species based on mitochondrial DNA, others argue that these findings are limited by the use of a single gene. Furthermore, the relationship between A. planci and its sibling species, the soft-bottom-dwelling A. brevispinus, highlights the starfish's adaptation to high-energy coral environments. Understanding these population dynamics and genetic structures is essential for developing effective reef conservation strategies, especially as environmental changes continue to influence their distribution and behavior.

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