Great Barrier Reef Fish Diversity Drops by Up to 75% Around Popular Areas
Great Barrier Reef fish populations have dropped 33-72% due to increased environmental disturbances.
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A 14-year study of coral reefs around inshore islands of Australia’s Great Barrier Reef has documented substantial declines in fish populations, particularly around popular, highly visited inshore areas. Scientists from James Cook University (JCU) and the Australian Institute of Marine Science observed fish communities at over 100 sites surrounding the Palm Islands, Magnetic Island, Whitsunday Islands and Keppel Islands. These reefs face recurrent disturbances like coral bleaching, cyclones and flood events, which have challenged the resilience of fish populations.
Coral bleaching
Coral bleaching occurs when corals expel the symbiotic algae living within their tissues in response to stress, such as high water temperatures. Without these algae, corals lose their color and are more susceptible to disease and death if conditions do not improve.The findings reveal reductions in both fish abundance and diversity, with populations decreasing by 33%–72% and fish species diversity dropping by 41%–75%, depending on the location. This study provides critical insights into the long-term impacts of environmental disturbances on fish populations in areas subject to human activities.
Inshore fish communities face mounting pressures
Fringing reefs around inshore islands, located closer to coastal populations, experience more intense human pressures. According to lead author Dr. Daniela Ceccarelli, a marine ecologist at the Australian Institute of Marine Science, reef fish populations in these inshore areas have less time to recover between stress events than those located further from the coast.
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Subscribe for FREEImpact of severe weather events on fish populations
The study found that major environmental events, such as the 2011 and 2013 floods, led to significant fish population declines in the Keppel Islands, where fish abundance fell to about 10% of pre-flood levels. While many locations saw partial recovery, the most affected sites remain largely overgrown with algae and exhibit minimal coral cover. Similarly, Cyclone Debbie in 2017 caused considerable damage to the Whitsunday Islands’ reefs, drastically reducing coral cover and available habitat for fish. This led to sharp declines in fish populations, particularly for species that depend on corals for shelter.
Mixed effects of no-take marine reserves
The study also found that marine protected zones where fishing is prohibited offered some protection for certain fish species, especially those targeted by fishers. However, Dr. Maya Srinivasan, a coral reef ecologist and co-author, highlighted that these reserves are unlikely to buffer all fish species from increasingly frequent environmental disturbances.
Shifts in fish community composition
The study observed that fish species dependent on coral habitats are particularly vulnerable to reef degradation, while herbivorous fish species like damselfish and parrotfish have shown population increases. These herbivorous species benefit from the algae-rich environments that develop on degraded reefs, yet this shift indicates a significant imbalance in the ecosystem.
Changing patterns of disturbance in the Anthropocene
The study underscores how traditional patterns of natural disturbances, such as cyclones and floods, are evolving in frequency and intensity due to human-driven climate change. Dr. Ceccarelli pointed out that these disturbances historically helped maintain diverse and complex marine ecosystems. However, under the current conditions of the Anthropocene, characterized by human-induced climate change, these events occur more frequently and with heightened severity.
Anthropocene
The Anthropocene is the current geological age, recognized by scientists as a period in which human activities significantly influence Earth's ecosystems and climate. Characterized by industrialization, habitat destruction, and climate change, this era is associated with environmental disturbances and biodiversity loss.Herbivorous fish
Herbivorous fish are species that primarily consume plant matter, including algae. Common examples in coral reef ecosystems include damselfish and parrotfish, which help control algae growth on reefs, contributing to a balanced ecosystem.Expanded monitoring to guide future conservation
Currently led by JCU’s TropWATER, the long-term monitoring program now covers eight key regions across the Great Barrier Reef, with 21 additional inshore islands included in recent years. This expanded monitoring will be essential for tracking changes in fish and coral communities and informing conservation strategies aimed at mitigating the impacts of climate change on these ecosystems.
“This adds to the mounting evidence that without global action on reducing emissions, protected areas and fisheries management alone are not sufficient to safeguard coral reef fish.”
Dr. Daniela Ceccarelli
Reference: Ceccarelli DM, Logan M, Evans RD, et al. Regional‐scale disturbances drive long‐term decline of inshore coral reef fish assemblages in the Great Barrier Reef Marine Park. Global Change Biology. 2024;30(10):e17506. doi: 10.1111/gcb.17506
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