El Nino and La Nina in Galapagos
The climate of the Galapagos Islands is shaped by powerful ocean currents and trade winds that converge at the Equator. Most years, these forces keep the archipelago’s weather fairly predictable: cool, nutrient-rich waters feed one of the most productive marine ecosystems on Earth, while the highlands receive gentle rainfall that sustains lush vegetation. But every few years, this balance shifts dramatically.
When the Pacific’s normal currents falter or reverse, the result is El Nino, a period of warm water, heavy rain, and marine scarcity. When they surge in the opposite direction, the islands experience La Nina, bringing cooler seas and drier skies. Together, these two oscillations, known as the El Nino–Southern Oscillation (ENSO), create the natural rhythm of boom and bust that defines life in Galapagos.
This map shows the Pacific Ocean during the 1982–83 winter, highlighting the unusually warm sea surface temperatures that characterised the event.
What causes El Nino and La Nina
Under normal conditions, the South Equatorial Current and Pacific trade winds push warm surface water westward across the ocean, drawing up cold, nutrient-rich water from the depths along the Galapagos platform. This process, called upwelling, fuels plankton blooms that feed fish, sea lions, penguins, and countless other species.
Every three to seven years, however, these currents weaken or even reverse. The upwelling slows, the cold water disappears, and the surface temperature around Galapagos rises from its usual 18 °C to nearly 30 °C. This is El Nino. The phenomenon was first noted centuries ago by Peruvian fishermen who called it El Nino de Navidad, “the Christ Child”, because it arrived around Christmas.
When the pattern flips and the currents strengthen, the opposite occurs: colder, nutrient-rich water surges to the surface, marine productivity soars, but rainfall dwindles. This cooler phase is La Nina.
The effects of El Nino – at sea
El Nino spells hardship for the sea. As nutrients vanish, the base of the food web collapses. Algae and plankton decline, starving fish and invertebrates, which in turn affects higher predators.
Historical records show the devastating scale of these events. During the 1982–83 El Nino, researchers documented the bleaching of coral reefs, the disappearance of red and green algae, and catastrophic losses across species. Even a small increase in ocean temperature can trigger coral bleaching, as corals expel the microscopic algae that sustain them, leaving their skeletons ghostly white and vulnerable to death.
Marine Iguanas
Around 67% of marine iguanas in some colonies perished. The loss of their preferred red and green algae leaves only brown algae, which they can barely digest. In an extraordinary act of adaptation, marine iguanas respond by shrinking their skeletons by up to 20%, even reabsorbing parts of their own bones. A smaller body needs less energy and warms more quickly in the sun, a life-saving trade-off until cooler waters return. On some islands, iguanas have even been observed nibbling on terrestrial vegetation in desperation, though this is rare and offers little nourishment.
Boobies and Penguins
Blue-footed boobies, Nazca boobies, and Galapagos penguins suffered population crashes of up to 70% during strong El Nino years, abandoning nesting sites when fish became scarce. Galapagos penguins, which rely on cold-water schools of fish, were particularly affected. Their numbers dropped by 77% in 1982–83 and 65% in 1997–98, and most pairs skipped breeding altogether.
Fur Seals and Sea Lions
Male fur seals were among the first to die as food supplies collapsed, and sea lion mothers struggled to feed their pups. Many colonies experienced widespread starvation as fish migrated into cooler waters.
Green Turtles
Green turtles face food shortages as the seaweed they graze on dwindles in warm water. The shift in ocean temperature also affects nesting behaviour and hatchling survival.
More recent events, such as 1997–98 and 2023–24, show the same pattern in milder form. Warmer seas reduce the algae that marine iguanas depend on, forcing them to shrink their skeletons to survive until cooler waters return.
The effects of El Nino – on land
While marine life suffers, El Nino brings abundance to the land. As warm water builds in the eastern Pacific, so do the clouds. Rainfall in Galapagos can increase tenfold, transforming arid landscapes into temporary green oases.
Land Birds
This burst of moisture fuels plant growth and insect life, triggering prolific breeding among finches, mockingbirds, and other landbirds. However, wetter conditions can also encourage diseases such as avian pox, which sometimes spread rapidly through island populations.
Giant Tortoises
For giant tortoises, El Nino brings both benefit and challenge. Lush vegetation provides ample food, helping tortoises grow and thrive, but excessive rainfall can flood nesting areas, wash away eggs, and disrupt reproduction cycles.
Land Iguanas
Some species, such as land iguanas, positively flourish. Heavy rainfall causes cactus pads (Opuntia spp.) to swell with water and collapse under their own weight, creating an abundance of fallen food. Iguanas feast on the moisture-rich pads and often increase in number during El Nino years.
Invasive Species
The same rains, however, also favour invasive species such as fire ants, rats, goats, cats, and tree frogs, which place increased pressure on native wildlife and fragile habitats. Their rapid spread during wetter periods can undo years of conservation effort.
In contrast, La Nina years bring the opposite conditions: cooler seas that enrich the marine ecosystem, but extended drought on land that tests terrestrial species and the resilience of those who depend on them.
The effects of El Nino – on humans
El Nino affects people as much as wildlife. Tourism, which supports most of the Galapagos economy, can suffer when key wildlife populations decline. Fishing communities face uncertainty as warm seas drive fish away and alter upwelling patterns. Flooding can damage infrastructure and increase mosquito populations, raising disease risks.
These environmental shifts ripple through local livelihoods and conservation programs alike. As Galapagos faces more frequent and intense ENSO cycles due to global climate change, monitoring and adaptation are essential. Scientists from the Galapagos National Park Directorate and international research teams continue to study El Nino’s effects on the islands, from marine iguana foraging behaviour to long-term ecosystem resilience.
Video: Explaining El Nino and La Nina
The short video (under 7 minutes) below offers a simple visual explanation of how El Niño and La Niña begin. It illustrates how shifting trade winds and ocean currents in the Pacific set off a chain of climate effects around the world, from flooding in Ecuador to droughts in Indonesia, and why these events matter so much to the Galapagos ecosystem.
Cycles of Change
The alternating cycles of El Nino and La Nina have shaped evolution in Galapagos for millennia. Many species, from penguins to tortoises, have adapted to endure scarcity and abundance in rhythm with the sea. But as the climate warms, models predict that these events will become both stronger and more frequent, pushing fragile ecosystems to their limits.
The story of El Nino in Galapagos is a reminder that life here is never static. The same forces that shaped Darwin’s observations continue to test the resilience of the islands today. It’s a delicate dance between ocean, climate, and the extraordinary wildlife that depends on both.
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