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Tara Pacific expedition - november 2017 North Ema Reef, Kimbe Bay, Papua New Guinea, 2 Crown-of-Thorns Starfish (Acanthaster planci) are being killed by a local dive guide, taking them out of the water.The Crown-of-Thorns Starfish (Acanthaster planci) feeds on branching corals and table-like corals, such as Acropora species. In experiments, large starfish (40 cm and greater diameter) killed about 60 cm²/day. Outbreaks are considered a danger for reefs. Some ecologists suggest that the starfish has an important and active role in maintaining coral reef biodiversity, driving ecological succession. Before overpopulation became a significant issue, crown-of-thorns prevented fast-growing coral from overpowering the slower growing coral varieties. D: 5 m. (KEYSTONE/BIOSPHOTO/Christoph Gerigk)