A groundbreaking study from the University of Newcastle has challenged long-standing assumptions about marine food webs and predator-prey relationships in Australia’s Great Southern Reef. Contrary to popular belief, large predatory fish such as the blue groper and pink snapper are not significantly preying on long-spined sea urchins—a native species linked to the spread of destructive “urchin barrens.”
What Are Urchin Barrens and Why Are They a Problem?
Urchin barrens are underwater zones where seaweed and kelp forests have been stripped away, often due to unchecked sea urchin populations. These barren areas dramatically reduce local biodiversity, lower ocean productivity, and absorb less carbon dioxide, making them a pressing concern for marine ecosystems and climate health.
In New South Wales, barrens have been strongly associated with overpopulations of Centrostephanus rodgersii—commonly known as the long-spined sea urchin. These areas are now spreading further south, notably into Tasmania, creating growing concerns among marine conservationists.
Key Findings: Predatory Fish Not Eating Long-Spined Urchins
Led by Ph.D. candidate Jeremy Day, researchers examined the stomach contents of 39 blue gropers and 111 pink snappers collected by recreational fishers along a 1,250 km stretch of the Great Southern Reef between 2021 and 2022. The results were published in the peer-reviewed journal Estuaries and Coasts.
“We were surprised to find almost no evidence that these large fish are preying on long-spined urchins,” Day explained. “Instead, they seem to consume other sea urchin species more frequently.”
Key Statistics from the Study:
- Blue Groper: Long-spined urchins found in only 5.1% of stomachs; other urchin species in 30%.
- Pink Snapper: Long-spined urchins detected in just 2.7%; other species present in 13%.
These findings indicate that while these fish may help regulate other sea urchin populations, they are not effective predators of long-spined sea urchins, contradicting previous ecological assumptions.
Implications for Reef Management and Conservation
The results are especially relevant given recent government interest in managing urchin barrens. In 2023, a Senate inquiry recommended a $55 million investment in combating long-spined sea urchin overpopulation. This new study highlights the need for more targeted strategies, as relying on natural predation by large fish may not be effective.
“Our research is an important piece of the puzzle in designing effective reef management strategies,” said Day. “It suggests the food webs of the Great Southern Reef are more complex than previously believed.”
Looking Ahead: Need for Advanced Research Methods
The research team emphasized the importance of expanding the study using molecular and isotopic dietary analysis techniques for more accurate insights into marine predation patterns.
Co-authors Dr. Megan Huggett (Senior Lecturer in Marine Science) and Associate Professor Troy Gaston (Associate Dean of Engagement and Outreach) also contributed to the project. The University of Newcastle remains committed to advancing sustainable solutions for marine resource management and climate resilience.
Citation:
Day, J.K., Huggett, M., & Gaston, T. (2025). Suspected Key Predators of Long-Spined Urchins Fail to Show Signs of Significant Predation in Gut Contents Analyses. Estuaries and Coasts. https://doi.org/10.1007/s12237-025-01518-z