Slaughter of coral-eating starfish protects Australia’s Great Barrier | Climate change

What can Australia do knowing that it faces what could be the worst summer for its Great Barrier Reef? Focusing on threats that can be acted upon directly, scientists suggest – which, in this case, means continuing to proactively and sustainably manage a species of starfish that devours corals alarmingly.

Cyclones, coral bleaching episodes and starfish outbreaks Acanthaster planci are the main factors in coral reef mortality in the region. It is difficult to control natural phenomena exacerbated by the climate crisis – such as the rise in ocean temperatures –, but it is possible to carry out targeted slaughter of the coral-eating species, also known as the crown-of-thorns.

“Resilience-based management is essential to protect ecosystems in the Anthropocene. Unlike large-scale climate threats to Great Barrier Reef corals, outbreaks of coral-eating crown-of-thorns starfish (Acanthaster) can be managed directly through targeted slaughter”, write the authors of a study published this Wednesday in the scientific journal Plos One.

The study evaluates the results of a decade of management strategies for these hungry sea stars with the aim of suppressing outbreaks and protecting coral reefs. Among the authors of the study are researchers from Great Barrier Reef Marine Park Authorityincluding the first author, Samuel A. Matthews.

Scientists compare the density of Acanthaster planci and coral cover during the third and fourth wave of outbreaks, in different areas of the coral reefs. The crown-of-thorns management strategy only began in the fourth wave of outbreaks, hence the interest in using the previous wave as a parameter.

The study suggests that reefs where there were higher levels of starfish culling saw greater increases in coral cover, while the rate of coral loss was more than 50% in areas where there was low culling effort.

“The clear coral protection results demonstrate the value of targeted manual harvesting as a scalable intervention to mitigate crown-of-thorns starfish outbreaks and a powerful resilience-based management tool to ‘buy time’ for coral reefs, protecting reef ecosystem functions and biodiversity as the climate changes”, reads the study of Plos One.

The species Acanthaster planci, or simply crown-of-thorns, feeds on coral polyps, from which it extracts nutrients. These sea stars are described as very voracious echinoderms and can have a devastating impact on reefs if populations grow too large.

A 2012 study, published in Proceedings of the National Academy of Sciencesindicated, for example, that this predator alone had been responsible for more than 4% of the damage that led, over 27 years, to the loss of more than half of the Great Barrier’s coral area.

Cyclones and other challenges

The Great Barrier Reef is facing multiple challenges this summer (in the Southern Hemisphere). In addition to the episode of massive coral bleaching – the fifth in a time window of eight years – Australia has cyclones, floods and the aforementioned outbreaks of hungry starfish on its list of challenges, according to an official report from the Australian government.

A further report from the Great Barrier Reef Marine Park Authority, which included a detailed study of 1080 reefs, precisely highlights the increase in cumulative impacts in this season. According to the document, 39% of the studied area was found to be affected by very high or extreme levels of bleaching, with the southern reefs showing the highest levels of bleaching. stress thermal.

The Great Barrier Reef has considerable weight in the country’s tourism sector, contributing around six million Australian dollars (3.6 billion euros) and representing approximately 64,000 jobs. In other words, there is an urgency on the part of national authorities to protect this natural heritage for environmental but also socioeconomic reasons.

The North American Agency for Atmosphere and Oceans (NOAA) had already warned in March that the entire planet was heading towards a fourth episode of massive coral bleaching, which could cause the death of vast areas of tropical reefs, including parts of the Great Barrier Reef.

Once exposed to very high temperatures, corals lose the colorful algae that inhabit their tissues and become colorless. O coral bleaching occurs following consecutive months in which record temperatures were recorded in the ocean, a phenomenon driven by climate change and worsened by the standard El Niño.