The Great Barrier Reef in Australia has been destroyed by its fourth catastrophic bleaching episode in less than a year. Scientists have stated that immediate action on climate change is required if the world's biggest reef system is to survive. But what about the fish who rely on these reefs?
There is significant fear that many species may become extinct after a new study published in the journal Proceedings of the Royal Society B showed that certain reef fish find it difficult to detect competition following major bleaching episodes.
Reef Fish Making Poorer Decisions, Getting Into Unnecessary Fights
Marine biology senior lecturer, Dr. Sally Keith at Lancaster University, said their study showed reef fish are making poor decisions that lead them to be less able to avoid unnecessary fights. Recognizing a competitor will help a fish decide whether to escalate or retreat from a contest to conserve energy and avoid injuries, MailOnline reported.
Dr. Keith added that these rules evolved from a particular playing field, but it seems to be changing due to mass coral bleachings in the past years. Repeated disturbances could alter the abundance and identity of corals and the food source of fish. It is unclear whether these fish, like butterflyfish, could update their rule book fast enough to adapt to their changing environments.
Researchers believe that changes in fish behavior could have implications for species' survival as climate change and global warming worsen, which might lead to further coral loss.
They conducted 3,700 observations on 38 butterflyfish species across five Indo-Pacific regions and studied how they behaved before and after mass coral bleaching. They found that encounters between fish of different species before the event resulted in chases 72% of the time, but it increased to 90% after one coral bleaching event.
Furthermore, they found that the distance these chases increased, which means fish expend more energy than they would have previously. They believe that as corals die, fish are forced to change and diversify their diets and territories, which causes them to act differently but not necessarily to their advantage.
This led to disruptions in relationships, which matured over thousands of years to allow other species to coexist. The team fears it will only worsen if global warming continues to heat the oceans and cause more mass coral bleaching events.
Coral Bleaching Disrupting Diversity in Fish
The Great Barrier Reef saw its first widespread bleaching episode in 1998. It was also witnessed in 2002, 2016, 2017, 2020, and 2022. The reef was revered for its kaleidoscope of color, but the mass coral bleachings have significantly affected it. A 2018 research by an international team of scientists reveals that coral bleaching events can also reduce the variety of fish living in these ecosystems.
The team noted that scientists have been studying the widespread impacts of heat stress on corals and are learning that some corals are more sensitive to heat stress than others. Reef fishes respond differently to these disturbances.
According to Science Daily, the loss of corals has caused a sharp drop in the diversity of fish communities as the mix of fishes has changed. Before the 2016 bleaching event at the Great Barrier Reef, experts noticed a significant variation in the number of fish species, total fish abundance, and functional diversity. Six months later, that diversity was almost lost.
RELATED ARTICLE : Awaiting the Evidence of Coral Bleaching to the Great Barrier Reef
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