Crown-of-Thorns Starfish: Predators Survive Heat Waves That Kill Corals by Eating Survivors

Corals may be relentlessly destroyed by heat waves, but predators, like crown-of-thorns starfish, live on by devouring other survivors, in addition to regenerating from cuts.

Juvenile Crown-of-Thorns Starfish vs. Heat Waves

Researchers at the University of Sydney discovered that juvenile crown-of-thorns starfish outperform their adult counterparts in tolerating heat waves, a concerning revelation with implications for coral reefs and climate change. These predator starfish, known for their destructive impact on the Great Barrier Reef, rank only below cyclones and bleaching events in coral mortality.

Led by Professor Maria Byrne, the recently published study found that juvenile crown-of-thorns starfish can endure heat levels causing coral bleaching nearly three times more effectively than adults. This implies that as adult starfish decline due to ocean warming, herbivorous juveniles can patiently transform into carnivorous predators, posing a threat to regenerating coral.

The research also identified contributing factors, such as their small size and versatile food consumption habits. This newfound resilience in juveniles intensifies concerns about the vulnerability of coral reefs in the face of climate change.

Outbreaks and Stresses

This discovery has significant implications for understanding climate change's impact on marine ecosystems, especially lesser-studied species. The rise in rubble habitat from coral bleaching may allow juvenile starfish populations to grow, potentially leading to adult starfish outbreaks.

This will, in turn, worsen the effects of climate change. These outbreaks may stem from overfishing of their predator, the giant triton, if not by natural factors. When corals are already stressed, crown-of-thorns starfish can be highly destructive, especially during coral bleaching or human-induced stresses.

Also Read: Starfish Facts: Misnamed Stars of the Oceans 

Eating Other Survivors and Regenerating From Cuts

Crown-of-thorns starfish employs a unique feeding strategy, extending their stomachs through their mouths to digest soft coral tissue while absorbing vital nutrients directly in the open environment. Concerns over their potential damage to local reefs have prompted collaborative efforts between fishermen and conservationists. Historically, attempts to control their population involved chopping them into pieces, which often led to regrowth.

Present methods focus on complete removal or targeted poisoning, sparing other reef species, especially corals.

In a fascinating twist, some animals like guard crabs, belonging to the Trapezia genus, have formed mutualistic relationships with specific corals. These crabs dwell among cauliflower and branching corals, actively defending their colonies from crown-of-thorns starfish. They employ tactics like pinching the starfish's tube feet and stomach lining.

In this symbiotic partnership, the crabs safeguard the coral colony from potential threats while securing a haven and protection from their predators. This intricate dance of predation and protection underscores the complex relationships within marine ecosystems.

Broadcast Spawning

Crown-of-thorns starfish reproduce via broadcast spawning, where multiple females release eggs and males release sperm simultaneously. This strategy enhances fertilization success and protects eggs from reef surface predators. Populations of these starfish fluctuate between high-density outbreaks and lower numbers. Although not exploited by humans, their local overabundance poses a threat to other species, making them a species of concern among scientists.

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