Coral re-bleaching caused by rising sea temperatures has led to lasting changes in fish communities, according to a new long-term study in Seychelles.
Large predatory fish, such as predators and many small fish, such as damsel, drastically decrease and are largely replaced by fish loving algae such as rabbit fish.
Publishing in the magazine Biology of Global ChangesResearchers have shown clear evidence that coral discoloration in 1998 has led to changes in biodiversity and constant changes in the range of fish species accompanying coral reefs that still exist today.
While some of the coral reefs exploded and recovered after bleaching, other reefs moved to algal fields.
Changes in fish communities are most evident in these algae-dominated reefs, but seaweed fish are the dominant part of the community on all reefs in the study.
Researchers believe that these same changes are likely to be found in similarly destroyed reefs around the world and could be described as a "new normal" state for post bleached reefs.
The research conducted by Lancaster University has been tracking the reef recovery in Seychelles for 16 years before another major coral bleaching event to affect reefs in 2016. Despite the length of time between these two large decaying corals, fish populations failed to recover until before – condition to cut.
Where previously there was a larger number of large predators, such as bites and group animals, as well as a large number of very small fish, such as damsels and butterflies, after bleaching a new community dominated by algal fish and rabbit fish and invertebrates such as emperors and passions, has taken over.
These changes have occurred because the structure of the habitats of the fish – corals – has collapsed. When coral does not recover, and algae take up space, the number and composition of fish change significantly.
Surprisingly, even in reefs where corals gradually recover between bleaching events, the number of fish species recovers but does not return to their original species composition.
Other studies have shown that the time between bleaching periods is now declining and is usually less than 10 years. In this study, the time from coral bleaching in 1998 to the next large is longer – 18 years – but fish communities have not yet been able to recover. This causes researchers to conclude that other reefs will undergo such changes, especially since bleaching events are becoming more frequent.
Dr. James Robinson of the University of Lancaster, lead author of the study, said: "Although the 18-year period between large mass whitening events has allowed the coral to recover to some reefs, we have found evidence that fish populations are unable to return to their pre-whitening levels, and they have been significantly altered to the reefs that become dominated by algae. The Seychelles-based study suggests that at current ocean warming levels – where the average frequency of bleaching is less than 10 years – constant changes in reef fish are likely on most coral reefs worldwide.
Professor Nick Graham of the University of Lancaster added, "The new normal coral reefs will be reef fish communities, which have fewer species and dominate herbaceous and invertebrate fish, which will change the way coral reefs and fishing opportunities coastal communities adjacent to coral reefs. "
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