Acanthaster
planci
(Linnaeus, 1758)
Acanthaster
planci is the large, well-known crown-of-thorns starfish. It
eats living coral, feeding by crawling over its prey, opening its mouth wide
and extruding its stomach over the coral. The coral tissue is digested in place
and sucked into the star, leaving a completely white and empty coral skeleton
that quickly gets covered by algae. Occasionally these stars overpopulate certain
areas, forming large herds that devour much of the coral on a reef. Causes for
these population blooms are still debated, but at times teams of divers have
attempted to prune down the Acanthaster populations on some reefs,
either by removing them from the water or injecting them with some poison that
kills the entire animal. Like most seastars, just chopping them up will not
help since starfish can regenerate from pieces. It has been questioned by some
whether such pruning attempts do good or harm. In any case, these should not
be handled unless you know what you are doing. The spines covering these stars
are pointed and sharp, easily puncturing a diver's skin and delivering a venom
that causes relatively intense pain. The venom also appears to have anticoagulant
properties, causing puncture wounds from the star to bleed for quite a long
time. These stars often hide during the day, suggesting they may be subject
to predation by daytime hunters. One fish reported to eat Acanthaster
is the humphead or Napoleon wrasse, Cheilinus
undulatus, which apparently does not mind the spines sticking into
its fleshy lips. The triton's trumpet shell, Charonia
tritonis, will also eat Acanthaster, and we have seen in Hawaii
the small harlequin shrimp, Hymenocera picta, riding around on a large
star, chopping off a leg at a time to eat. Acanthaster can reach about
half meter in diameter.
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