A team of researchers have identified unexpected ways coral reef fish living in the warmest waters on earth, in the Arabian Gulf, have adapted to survive extreme temperatures.

Some coral reef fish are more resilient to climate change than previously thought.

 July 01, 2024

Led by John Burt, co-principal investigator at the Mubadala Arabian Centre for Climate and Environmental Sciences (Access) at New York University (NYU) Abu Dhabi, and Jacob Johansen, associate research professor, Hawaii Institute of Marine Biology, the team discovered adaptations in both metabolism and swimming abilities that help fish survive the conditions of the Arabian Gulf. Surprisingly, these fish did not follow leading theoretical predictions, which expected that the maximum size of fish should be reduced due to limitations in metabolic oxygen-supply. Instead, these fish demonstrated a capacity to maintain efficient oxygen supply to fuel performance even at elevated temperatures.l

The warming of our oceans is anticipated to drastically affect marine life and the fishing industry, potentially upsetting entire ecosystems and economic structures reliant on these habitats. Current scientific models predict that by 2050, coral reef fish could shrink by 14 to 39 per cent in size due to increasing temperatures under climate change. The study’s findings challenge the prevailing view that oxygen supply limitations in larger fish are the main reason for smaller fish in warmer waters — the so-called “shrinking of fish phenomenon.” The species observed did not follow this pattern, suggesting that other factors are also at play.

The study proposes a new theory that the decrease in fish sizes and their survival in increasingly warm oceans might be more closely related to an imbalance between how much energy fish species can obtain and how much they need to sustain themselves.

In the paper published in the journal Nature Communications, the researchers compared two species of fish, Lutjanus ehrenbergii and Scolopsis ghanam, surviving under the elevated temperatures within the Arabian Gulf to those of similar age living in the cooler, more benign conditions in the nearby Gulf of Oman. Specifically, the researchers set out to determine what qualities reef fish in the Arabian Gulf have that enable them to survive there, where typical summer water temperatures are comparable to worst-case ocean warming projections for many tropical coral reefs globally by 2100.

“The hottest coral reefs in the world are an ideal natural laboratory to explore the future impact of rising water temperatures on fishes. Our findings indicate that some fish species are more resilient to climate change than previously understood and help explain why smaller individuals are evolutionarily favoured at high temperatures,” said Burt. “This has significant implications for our understanding of the future of marine biodiversity in a continuously warming world.”

https://gulfnews.com/uae/environment/fish-in-warm-waters-surprise-scientists-challenge-assumptions-1.103379694

link to full research article

Impacts of ocean warming on fish size reductions on the world’s hottest coral reefs

https://www.nature.com/articles/s41467-024-49459-8

Nature Communications volume 15, Article number: 5457 (2024) Cite this article

Abstract

The impact of ocean warming on fish and fisheries is vigorously debated. Leading theories project limited adaptive capacity of tropical fishes and 14-39% size reductions by 2050 due to mass-scaling limitations of oxygen supply in larger individuals. Using the world’s hottest coral reefs in the Persian/Arabian Gulf as a natural laboratory for ocean warming – where species have survived >35.0 °C summer temperatures for over 6000 years and are 14-40% smaller at maximum size compared to cooler locations – we identified two adaptive pathways that enhance survival at elevated temperatures across 10 metabolic and swimming performance metrics. Comparing Lutjanus ehrenbergii and Scolopsis ghanam from reefs both inside and outside the Persian/Arabian Gulf across temperatures of 27.0 °C, 31.5 °C and 35.5 °C, we reveal that these species show a lower-than-expected rise in basal metabolic demands and a right-shifted thermal window, which aids in maintaining oxygen supply and aerobic performance to 35.5 °C. Importantly, our findings challenge traditional oxygen-limitation theories, suggesting a mismatch in energy acquisition and demand as the primary driver of size reductions. Our data support a modified resource-acquisition theory to explain how ocean warming leads to species-specific size reductions and why smaller individuals are evolutionarily favored under elevated temperatures.