Breaking the Mortality Bottleneck: Giving Reef Fish a Better Start
Healthy fish populations are essential to the health of coral reefs, increasing resilience of these fragile ecosystems. However, many fish don’t live past their earliest days – a phenomenon known as the ‘mortality bottleneck’. Alan Gojanovic, a PhD Student at the University of Western Australia, explains how IMarEST funding has helped him on his journey to help fish survive and thrive on the reef.
Coral reefs are among the most vibrant and productive ecosystems on Earth. They are home to a dazzling array of species and provide benefits that extend far beyond the reef itself. For humans, reef fish sustain food security, support coastal economies, and draw millions of visitors each year.
So how do we ensure that reefs stay healthy? Interestingly, it’s often fish that hold the key: grazers keep algae in check, predators maintain balance, and the sheer abundance of fish helps drive the resilience of these ecosystems.
Yet, the very survival of reef fish is often determined in their earliest days on the reef. After drifting for weeks in the open ocean, tiny reef fish larvae make the critical transition to life on the reef in a process known as settlement. It’s a dangerous time for the juvenile fish as they are extremely likely to be eaten within 48 hours of arriving on the reef.
This mortality bottleneck, made worse by anthropogenic stressors such as climate change and overfishing, limits the ability of fish populations to replenish themselves and contributes to global declines of reef fish. This, in turn, is bad for the health of coral reefs worldwide.
A promising tool: post-larval capture, culture, and release
One emerging approach alleviating the problem is the Post-larval Capture, Culture, and Release method (PCCR). It’s a technique where larvae are collected just before settlement, reared in captivity for a short period to get them past the danger zone, and then released back onto reefs at a more robust stage.
What makes PCCR exciting is its simplicity. It requires little more than basic equipment, is inexpensive, and can be implemented in many locations without high-tech facilities.
However, despite its promise, PCCR remains underexplored. There is still much to learn about how different factors influence survival. For instance, we don’t understand whether the length of time fish are reared, or the time of day they are released make a difference.
My PhD research has focused on testing these questions, with encouraging results. In some cases, we recorded post-release survival rates for damselfish as high as 75% over 48 hours, compared to natural survival of only 25–38% in the same period. These findings suggest that even small interventions can make a substantial difference to the odds of survival during this critical life stage.
Beyond the numbers, PCCR offers a practical pathway for conservation because it affordability and scalability make it particularly appealing for conservation initiatives in local communities or holiday resorts, where resources are often limited but the need for action is urgent.
Sharing PCCR with the world
Earlier this year, I had the privilege of presenting this work at the 12th Indo-Pacific Fish Conference (IPFC) in Taiwan. During my talk titled “Effects of Captivity Duration and Release Timing in Post-Larval Capture, Culture, and Release (PCCR)” I was able to showcase the potential of the method and have valuable conversations with scientists from across the globe.
The conference was a great chance to share ideas, hear about the latest advances in reef fish ecology, and connect with others who share a passion for coral reef conservation.
This opportunity was made possible with the support of the IMarEST student bursary, which helped me attend IPFC and bring the story of PCCR to a wider audience. The bursary helped amplify my voice at an international stage, allowing me to highlight a tool that could make a real difference to sustaining reef fish populations.
For me, the experience underscored the value of collaboration and knowledge-sharing in tackling the immense challenges facing our oceans. Scientists, conservationists, and other marine professionals each hold part of the solution. By working together and by supporting the next generation of marine researchers, we can push forward creative, practical strategies like PCCR to help secure a future for coral reefs and the communities that depend on them.
This work was supported by the Australian Coral Reef Resilience Initiative (ACCRI), jointly funded by BHP and the Australian Institute of Marine Science.
