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Crown-of-thorns starfish are nature’s ultimate coral predators, and they are winning

Recent studies from the University of Sydney have illuminated a grim reality for coral reefs globally. Juvenile crown-of-thorns starfish, notorious predators in coral environments, are exhibiting an unexpected resilience to heatwaves, surpassing the very corals they prey upon.

This discovery not only highlights a disturbing imbalance in reef ecosystems but also signals potential accelerations in the devastation of coral populations, which are already struggling due to climate change.

Unseen threat to coral reefs

Crown-of-thorns starfish (COTS) are no strangers to the warm waters of the Great Barrier Reef and the broader Indo-Pacific region. These marine animals, while native, are considered a species of concern.

Their capacity for destruction is eclipsed only by phenomena such as cyclones and coral bleaching events. However, the new research indicates that these starfish might pose an even greater threat as the planet continues to warm.

In a disturbing twist, it appears that these starfish are not just survivors but potential opportunists in the face of climate change, with their juveniles patiently biding their time before wreaking havoc on recovering coral communities.

Crown-of-thorns starfish like the heat

Led by Professor Maria Byrne, this study emphasized the surprising tolerance of juvenile COTS to increased water temperatures. These young starfish can withstand conditions almost threefold those that trigger coral bleaching, presenting an alarming scenario for coral recovery amidst frequent environmental stressors.

“This is an important finding that has implications for understanding the impacts of climate change on marine ecosystems, especially the influence of understudied small cryptic species,” explained Professor Byrne.

The resilience of juvenile COTS contrasts starkly with the vulnerabilities of coral populations, which experience bleaching and mortality with a mere 1-3 degrees Celsius increase above the typical summer maximum.

Waiting game in warming waters

One of the most sinister aspects of this discovery is the patient nature of the COTS’ lifecycle. While adult populations might decline due to various factors, including a lack of prey or increased temperatures, the juveniles can survive for extended periods on alternative diets.

The rubbles of dead corals, a byproduct of bleaching events and starfish feeding frenzies, offer an ideal habitat for these juvenile starfish. Here, they can sustain themselves and wait, sometimes for up to six years, for the corals to return. Then, as the reefs begin to show signs of life, these juveniles mature and commence their destructive feeding, continuing a vicious cycle.

Compounding factors in starfish survival

The study also identified specific characteristics contributing to the juvenile starfish’s survival in increasingly hostile conditions. Their small size potentially diminishes their physiological needs, while their flexible diets mean they don’t solely rely on corals for sustenance.

These adaptations make them particularly suited to capitalize on the adverse conditions climate change creates. “The heat resistance and potential for the juveniles to gradually build-up in the reef infrastructure in coral rubble over years might be a phenomenon contributing to the initiation of adult crown-of-thorns starfish outbreaks,” said Matt Clements, a PhD student and co-author of the study.

COTS push ecosystems to their tipping point

The implications of this research are vast and concerning. Currents threats like overfishing, nutrient build-up, and now the resilience of COTS to warming waters are pushing coral ecosystems to their limits. The crown-of-thorns starfish, with their newfound advantage, are positioned to be not just beneficiaries of a changing ocean environment but active participants in the decline of coral reefs.

This study underscores the urgency with which we need to address climate change and its multifaceted impacts on vulnerable ecosystems. Understanding the interactions between predator and prey resilience in the face of environmental stressors is crucial for implementing strategies that will protect and preserve these biodiverse underwater landscapes for future generations.

The full research paper is published in the journal Global Change Biology

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