Acanthaster planci—the crown‑of‑thorns starfish (COTS)—is a major coral predator on Indo‑Pacific reefs (family Acanthasteridae). It bears numerous venomous spines and typically 12–20 arms. By everting the stomach it feeds on live tissues of scleractinian corals. At natural densities it can promote coral turnover, but during outbreaks it rapidly strips reefs of corals.
Ecology & Biology
Diet: prefers reef‑building corals (e.g., Acropora), digesting tissues via external digestion.
Reproduction: broadcast spawner with extremely high fecundity; larvae are planktonic and widely dispersed.
Predators: include the giant triton Charonia tritonis, humphead wrasse Cheilinus undulatus, puffers and certain crustaceans.
Outbreak drivers: a combination of nutrient enrichment (larval survival), predator depletion and oceanographic transport/settlement events.
Identification
Large disc with many arms (commonly 12–20, range ~7–23) and dense, long toxic spines dorsally. Colour varies from grey‑violet and reddish‑brown to bluish‑green depending on region and individual.
Size & Longevity
Size: arm‑to‑arm diameter typically 25–60 cm, exceptionally 80 cm+.
Life: about 3–8 years depending on food and conditions.
Range & Habitat
Widespread across the tropical Indo‑Pacific on shallow reef slopes, flats and crests.
Conservation & Management
Impact: outbreaks can slash coral cover within weeks to months and alter fish assemblages and ecosystem services.
Control: targeted culling (mechanical removal) and injections (e.g., vinegar/citric acid/bile salts) are effective; watershed nutrient control and predator protection are long‑term solutions.
IUCN: taxonomy is under revision (regional forms/cryptic species); statuses vary by entity. This overview is marked Not Evaluated (NE).
