Israel fish deaths linked to rapid warming of seas

https://www.theguardian.com/science/2020/sep/21/israel-fish-deaths-linked-to-rapid-warming-of-seas

 Natalie Grover
Mon 21 Sep 2020 15.00 EDT

High temperatures and the persistent warming of oceans have triggered profound changes in marine ecosystems, but a new study suggests that the rate of onset of warming – rather than the peak – could also play a key role in the damage fuelled by climate change.

In early July 2017, researchers were drawn to the coast of Eilat, Israel, following sightings of fish carcasses, a rare occurrence in the region’s coral reefs.

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The same pattern emerged in two earlier documented mass coral reef fish deaths in Kuwait Bay in 2001 and western Australia in 2011. Both were immediately preceded by rapid warming spikes, suggesting that the rapid onset of warming, regardless of the final temperature, might trigger widespread mortality, the researchers wrote in the Proceedings of the National Academy of Sciences.

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“Ocean systems are being stressed out in many different ways – and like the background stress of Covid-19 on people, it makes everything else in life just that much more difficult,” he said.

When you add events such as sudden warming to overfishing, pollutants, changes in ocean acidity and oxygen levels – the abruptness of it can be devastating because fish are already metabolically and physiologically stressed, he suggested.

It is unlikely coral reef fish will swim to cooler water to escape, given their shallow habitat, he added. “There’s no food there, no grocery stores for them in deep water.”

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“What you have here is one biotic (bacterial infection) and one abiotic (increase in temperature) challenge that occurred at the same time. It is possible that the infection lowered the thermal tolerance of the fish, and this resulted in the number of mortalities … but it certainly is very unlikely that it was temperature alone,” said Dr Kurt Gamperl from the Memorial University of Newfoundland, Canada, who was not involved in the study.

The authors did not make any direct connection between the mortality and the rapid warming, he cautioned. “The evidence is all circumstantial.”