In the usually warm waters off Indonesia’s Mulut Kumbang Strait, something extraordinary happens when the sea suddenly turns cold. The temperature can drop so fast that small fish become stunned — and within hours, dolphins arrive in droves to feed.
A new study published in Progress in Oceanography (October 2025) has revealed this fascinating link between rare ocean events and dolphin behavior. The phenomenon, known as an Extreme Upwelling Event (EUE), is caused when powerful winds and deep-sea currents push cold, nutrient-rich water up to the surface.
A Shock Beneath the Waves
Under normal conditions, the tropical surface water in the region stays warm year-round. But during an EUE, the sudden rush of deep water can cool the surface by more than 10 degrees Celsius. For small fish and other marine creatures adapted to the warmth, this rapid change can be devastating.
“They’re essentially shocked by the cold,” Anindya Wirasatriya, the researchers from Diponegoro University, Indonesia explained in the study. Many fish become sluggish or lose consciousness altogether — floating helplessly near the surface.
That’s when the dolphins come. Fishermen and local observers noticed that dolphin sightings soared during these cold-water surges. The animals seemed to appear out of nowhere, circling the area and diving repeatedly into the chilled sea to feed.
For the dolphins, these events are like an all-you-can-eat buffet. “EUEs make prey more accessible, and dolphins take full advantage,” the scientists wrote.
Using satellite temperature data, time-lapse cameras, and direct field observations, the team confirmed that dolphin activity consistently peaked during and immediately after upwelling events.
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Nature’s Dolphin Behaviour
Upwelling isn’t new — it’s a vital process that nourishes marine ecosystems around the world. When deep, nutrient-rich waters reach the surface, they feed plankton, which in turn supports fish and larger predators.
What makes the Mulut Kumbang case so striking is how quickly the event unfolds — and how dramatically it reshapes animal behavior. Within a day, the entire food chain reorganizes: plankton bloom, fish freeze up, and dolphins feast.
The researchers suggest that EUEs might become more frequent or more intense as climate change alters wind patterns and ocean circulation. While that might sound like good news for dolphin feeding, the broader ecological effects are still uncertain. Repeated shocks could stress fish populations, disrupt breeding, and change how energy moves through the ocean’s food web.
A Glimpse into the Future Sea
For marine biologists, these events offer a living experiment — a chance to watch how animals adapt when the ocean itself behaves unpredictably. Dolphins, it turns out, are keenly attuned to such shifts.
“They seem to know when the sea is about to turn,” Anindya said again. “The moment the temperature drops, they’re already there.”
As the planet warms, extreme phenomena like these could become more common, revealing both the resilience and fragility of ocean life.
The sight of dozens of dolphins slicing through icy waters in the tropics might seem magical, but it’s also a reminder of how tightly life in the sea depends on temperature — and how quickly that balance can change. (Sulung Prasetyo)
