As warming seas threaten coral reefs across the globe, a small, unassuming coral in the Mediterranean Sea is defying the odds. Oculina patagonica, a modest species that doesn’t build massive reefs or depend entirely on algae for survival, is not only enduring rising temperatures that devastate other corals it’s thriving.

A Coral That Breaks the Rules

Most corals rely on a delicate partnership with microscopic algae called zooxanthellae, which live inside their tissues. These algae perform photosynthesis, providing energy that fuels coral growth. When seawater gets too warm, the relationship breaks down the coral expels the algae, turns ghostly white, and often dies in a process known as coral bleaching. Oculina patagonica, however, plays by different rules. When Mediterranean waters climb past 29°C (84°F), it too bleaches, but instead of dying, it switches survival modes. The coral continues to live without its algae, feeding directly on plankton and organic matter until temperatures drop and its symbiotic partners return. That remarkable ability to live independently and later rebuild its partnership has made Oculina a subject of fascination for marine scientists seeking hope in a warming ocean.

An Ancient Survivor Hidden in Plain Sight

First described near Genoa, Italy, in 1966, Oculina was once thought to be an Atlantic invader. Decades of research later, scientists realized it had long been a native Mediterranean species, quietly persisting for millions of years in small, overlooked colonies. Today, Oculina is spreading rapidly across shallow Mediterranean coasts, thriving in waters that swing dramatically from under 10°C in winter to above 30°C in summer.

“When first documented in Levantine waters, it was thought that O. patagonica would not survive because summer temperatures were too high,” explained Dr. Shani Levy from the Centre for Genomic Regulation (CRG) in Barcelona. “But against all predictions, it established itself and populations are growing.”

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Life Without Algae: A Hidden Superpower

When Oculina’s algae vanish, the coral shifts from photosynthesis-based nutrition to heterotrophy feeding by capturing prey from its surroundings. Its cells reconfigure: digestive tissues expand, and immune-like cells clear away dying algae-hosting cells, allowing the coral to feed directly on plankton and organic detritus.

“Oculina’s ability to live without a photosynthetic partner allows it to thrive in deeper or murkier waters where light is limited,” said Dr. Xavier Grau-Bové, one of the study’s co-authors. “That’s a huge advantage in the human-altered Mediterranean Sea, where turbidity from shipping and sedimentation is increasing.”

This adaptability means Oculina can persist where other corals fail not by resisting stress, but by outsmarting it.

Inside the Coral’s Molecular Playbook

To uncover the secrets of Oculina’s resilience, researchers examined its genome and single-cell biology, comparing it to two tropical coral species highly dependent on algae. They discovered that Oculina’s cells behave like a biological hybrid, able to toggle between two energy modes. When algae are present, Oculina absorbs fats and lipids produced through photosynthesis, building long-term energy reserves. When algae are gone, it reverts to its primitive feeding machinery, hunting and digesting particles from the water column. According to Professor Arnau Sebé-Pedrós, who co-led the study, this flexibility isn’t a new trick, it’s an ancient ability that other corals may still possess but rarely use.

“Oculina didn’t invent a new lifestyle,” Sebé-Pedrós said. “It reactivated old genetic pathways tools that many corals still have, but which remain dormant.”

A Glimpse into the Future of Coral Survival

The Mediterranean Sea serves as a natural stress lab, a semi-enclosed environment with extreme swings in temperature, salinity, and nutrient flow. That volatility makes it a testing ground for climate resilience.

“It acts like a preview of what’s to come for other oceans,” said Dr. Levy. “Species that can handle these extremes give us valuable clues about adaptation.”

Still, Oculina’s success doesn’t mean the global coral crisis is over. Unlike tropical reef-builders such as Acropora, Oculina doesn’t form massive calcium carbonate structures that support marine ecosystems. Its resilience offers hope for adaptation, not a replacement for the world’s vanishing reefs.

“The best way to help any marine ecosystem withstand this warming world will always be to prevent the warming in the first place,” added Dr. Grau-Bové.

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Resilience Rooted in Evolution

The study, published in Nature, reframes how scientists think about coral survival. Oculina’s endurance shows that evolutionary memory, the ability to switch between ancient and modern survival modes may be more widespread than previously believed. In a time when ocean heat records are breaking year after year, the coral’s story stands as a reminder that nature often holds solutions hidden in plain sight. The challenge now is not only to understand those strategies but to give them a chance by keeping oceans stable enough for resilience to matter.

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