Life on the Great Barrier Reef is experiencing major transformations due to climate change and various human-induced pressures, according to a recent study. Reef fish play an essential role in marine ecosystems, contributing to food security, controlling seaweed growth, and generating sand for beaches, providing numerous benefits for both humans and coral reefs. Recent research conducted by an international team of marine scientists from the UK and Australia, led by researchers at Lancaster University and published today in the journal Nature Communications, highlights significant changes in the fish communities of the Great Barrier Reef, the largest coral reef system in the world.
Life on the Great Barrier Reef is experiencing major transformations due to climate change and various human-induced pressures, according to a recent study.
The fish in these reefs are crucial for many reasons, including ensuring food security, managing seaweed growth, and even contributing to the formation of sandy beaches.
Research from an international team of marine scientists, led by Lancaster University and including experts from the UK and Australia, shows that fish communities on the Great Barrier Reef have undergone notable changes since the 1990s, with the rate of transformation increasing. This calls into question long-established patterns of biodiversity around the globe.
Interestingly, the study found that coral diversity—rather than just coral quantity—plays a critical role in supporting the fish species that rely on coral reefs.
The Great Barrier Reef faces numerous challenges, with issues like coral bleaching and cyclones becoming more severe and frequent in recent years. Extreme heat stress has led to six major coral bleaching events between 1998 and 2022, with an additional event occurring in 2024 after the completion of this study. These challenges are exacerbated by factors such as tropical storms, water pollution, and outbreaks of crown-of-thorns starfish, impacting coral reefs by altering the amount and composition of coral, as well as the diversity of fish inhabiting these reefs.
The research team utilized data from the Australian Institute of Marine Science’s (AIMS) Long-Term Monitoring Program, which has been surveying fish and coral for over three decades, from 1995 to 2022. The monitoring covers more than 1,200 km of the Great Barrier Reef (from 14°S to 24°S).
One notable observation in biodiversity is the ‘latitudinal diversity gradient’, where species richness typically increases as one approaches the Equator. This study has revealed significant fluctuations in this gradient.
Traditionally, latitudinal diversity patterns have remained stable over long geological periods, with these patterns also reflected in fossil records. However, the study indicates that while the Great Barrier Reef still aligns broadly with this pattern, there are emerging signs that it might be changing due to mounting pressures.
In the northern sections of the Great Barrier Reef, closest to the equator, the diversity of fish, particularly omnivores, plankton feeders, and herbivores, has declined. Conversely, these groups have increased in the southern parts of the reef, raising questions about the potential impacts on this ecosystem’s function.
The southern areas of the Great Barrier Reef have seen significant fluctuations in reef fish diversity—alternating between periods of high species variety and times of very low diversity.
The researchers not only documented changes in the number of fish species but also examined how the makeup of fish communities has evolved. They found ongoing changes in fish communities as species are replaced in response to disturbances, which have become more frequent over time.
Javier González-Barrios, the lead author and a PhD researcher at Lancaster University, commented, “Our results indicate that the biodiversity of the Great Barrier Reef is experiencing long-term and significant changes due to ongoing disturbances driven by climate change. Since monitoring began in the 1990s, both the number of fish species and their composition have changed remarkably, and these shifts continue as pressures on the reef intensify.”
“We have observed not only changes in the numbers and make-up of fish species throughout the reef but also an increase in species turnover, where one species replaces another, which is accelerating in recent years with no signs of stabilization.”
“These changes offer important insights into established geographical patterns, such as the latitudinal diversity gradient, and pose questions about whether these patterns are diverging from their original driving factors.”
Another important insight from this study is that changes in coral species composition serve as a better predictor of shifts in fish patterns than merely looking at the percentage of hard corals—a common measure used to evaluate coral reef health.
“The Great Barrier Reef has seen dramatic changes, with many reefs experiencing cycles of hard coral decline followed by recovery after significant disturbances,” noted Dr. Mike Emslie from AIMS. “However, just focusing on coral cover can obscure the underlying shifts in coral species composition. Corals create a three-dimensional habitat structure that supports various organisms, including fish, and the diversity of coral species can significantly influence the complexity of that habitat. If some coral species recover but do not provide the same structural complexity, this can affect the fish communities that depend on it.”
“Our study illustrates that changes in fish diversity on the Great Barrier Reef were closely linked to shifts in coral composition, much more so than fluctuations in coral cover, underscoring the essential role of a diverse coral community for sustaining reef fish populations.”
Professor Nick Graham from Lancaster University added, “Reef fish play an essential role in several ecosystem processes, including managing seaweed to prevent its overgrowth on ocean floors, and contributing to the sand we enjoy on tropical beaches. They are also crucial for fisheries and a vital food source for millions around the world. With disturbances growing more frequent and severe, the traditional patterns of fish diversity and abundance we have relied on are changing, which will impact the benefits these fish provide for ecosystems and for us. It’s crucial that we enhance our understanding of the changing biodiversity patterns on coral reefs, along with the ecological and social consequences of these changes.”
The authors of the paper include Javier González-Barrios, Sally Keith, and Nick Graham from Lancaster University, Michael Emslie and Daniela Ceccarelli from AIMS, and Gareth Williams from Bangor University.
The Australian Institute of Marine Science (AIMS) is a government-funded organization in Australia that supports the Long-Term Monitoring Program. Javier González-Barrios received funding from a Natural Environment Research Council (NERC) studentship through the Envision Doctoral Training Centre.
