Crown-of-Thorns

DCIM999GOPRO

The Crown-of-Thorns (CoT) sea star (Acanthaster planci) can pose serious threat to Pacific coral reefs. The CoT varies from traditional sea stars in that it may have anywhere from 7 to 23 limbs and possesses numerous, long, sharp, toxic spines. In normal quantities this invertebrate is an appropriate part of the Pacific reef ecosystem. However, recent, increased, massive outbreaks of CoTs are highly problematic because the CoT is a corallivore, meaning it feeds on coral. Thus, outbreaks have the potential to destroy entire reefs. The CoT eats the fleshy polyps of a stony coral colony leaving behind white scars of the remaining dead calcium carbonate coral skeleton. In a balanced ecosystem CoTs feed on fast-growing Acroporid coral species, however when CoT numbers are abundant they begin feeding on slow growing coral colonies like Porites, which can devastate reefs for many years into the future.

Natural predators of the adult CoT include titon triggerfish (Balistoides viridescens), white-spotted pufferfish (Arothron hispidus), napoleon wrasse, humphead wrasse (Cheilinus undulates), giant triton snails (Charonia tritonis) and painted shrimp (Hymenocera picta). Overfishing of these predators, particularly the Giant Triton, valued for its large, beautiful shell, may have led to increased CoT outbreaks. Furthermore, it is possible that our wastewater and fertilizer have also contributed to these outbreaks. Scientists theorize that nutrient-rich runoff into the ocean from human activities has enabled more CoT larvae to survive, because CoT larvae feed on planktonic algae and an increase in nutrients favors excessive algal growth. Thus more nutrients –> more algal –> more CoTs –> greater damage to coral reefs.

Methods of CoT control:

  • Land Disposal
    • Collect CoTs, handling them with large serving tongs. Bring them to land and bury them.
    • When stressed CoTs will attempt to spawn, therefore it is essential to remove them from the water as quickly as possible.
  • Cutting up and Crushing in situ
  • Tying in bags in water
  • Poison Injection (acetic acid or sodium bisulfate)
    • Injection causes the CoT to disintegrate
  • Using dead CoTs as material for compost has been practiced in Fiji

Currently, we are exploring these methods at my site and will be developing a removal program in the future!

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