CrownofThorns

Crown of thorns, or crown-of-thorns starfish, refers to Acanthaster planci, a large predatory starfish native to Indo-Pacific coral reefs. It is named for the crown-like arrangement of long, venomous spines covering its upper surface. Adults can reach roughly 60 cm to 1 meter in diameter and display a range of colors from purple and brown to orange.

Crown of thorns inhabits tropical reef ecosystems, typically on shallow to mid-shelf areas. It is mainly active at night and feeds on hard corals, using its everted stomach to digest polyp tissue. When present in high densities, it can consume substantial portions of coral colonies, hindering reef growth and recovery.

Reproduction is sexual and involves broadcast spawning. During breeding, females and males release eggs and sperm into the water column, fertilization occurs externally, and planktonic larvae pass through several stages before settling as juvenile starfish. Under favorable conditions, populations can surge, leading to outbreaks that may persist for years.

Outbreaks have caused extensive coral loss in various Indo-Pacific regions, reducing reef complexity and resilience. Natural controls include predators and competition, but human factors such as overfishing of predators and nutrient pollution can promote outbreaks. Management strategies focus on rapid removal of actively feeding individuals, targeted toxin injections, and efforts to restore predator populations and reduce nutrient inputs.

Crown of thorns exemplifies how a mobile coral predator can shape reef dynamics and emphasizes the importance of balanced predator–prey interactions for reef health.