Israeli study: Rate of sea warming, not just temperature, linked to fish deaths

Researchers say mass mortality occurred in Eilat during rapid warming episode in 2017, even though the temperatures themselves were not extraordinarily high

Tropical fish at the Eilat Dolphin Reef. (Asaf Zvuloni/ Israel Nature and Parks Authority/FLASH90)
Tropical fish at the Eilat Dolphin Reef. (Asaf Zvuloni/ Israel Nature and Parks Authority/FLASH90)

An Israeli study suggests that the rate at which sea temperatures rise — and not necessarily the peak heat they reach — can play a central role in ecological damage caused by climate change, including widespread mortality of otherwise healthy reef fish.

The study was published in the prestigious Proceedings of the National Academy of Sciences. It followed a 2017 case in Israel’s southern Red Sea resort town of Eilat, when scientists recorded the steepest rise in water temperature in 32 years, with a jump of 4.2 °C (39.56 °F) in two and a half days. They found that despite the peak temperature of the water not actually breaking any records, many fish deaths were recorded.

Collected carcasses of fish were found to be severely infected with the Streptococcus iniae bacteria. It is not clear what mechanism exactly allowed the bacteria to hit the fish so hard.

After comparing their findings to two other instances of mass fish deaths also preceded by a swift rise in water temperature, the researchers were led to believe there was a link between the two.

A scuba diver checks coral reefs in the Red Sea off the southern Israeli resort city of Eilat, June 12, 2017. (AFP PHOTO / MENAHEM KAHANA)

“What you have here is one biotic (bacterial infection) and one abiotic (increase in temperature) challenge that occurred at the same time,” Kurt Gamperl from Memorial University of Newfoundland, Canada, not involved in the study, told the Guardian.

“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.”

Earlier this month, two Tel Aviv University researchers indicated that species of reef-building corals off the coast of Eilat and neighboring Aqaba in Jordan may be facing extinction due to changes in the environment where they reproduce.

Prof. Yossi Loya and PhD candidate Tom Shlesinger of Tel Aviv University’s School of Zoology warned that ocean warming and pollution may be changing the extraordinary way in which corals synchronize the release of eggs and sperm, leading to declining growth rates.

According to the scientists, whose groundbreaking study appeared in Science, the potentially catastrophic phenomenon could spread.

According to the United Nations, ocean acidity — caused by the absorption of increased carbon dioxide that results from human activity — has risen by 30 percent since the beginning of the Industrial Revolution. This is 100 times faster than any change in acidity experienced by marine organisms for at least the last 20 million years. Business-as-usual scenarios for carbon dioxide emissions could make the ocean up to 150% more acidic by 2100, the UN has warned.

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