As the 2026 El Niño strengthens in the equatorial Pacific, satellites are capturing the first major signs of disruption to the marine food web.
According to by NASA’s Earth Observatory observations, satellite measurements show a substantial drop in surface concentrations of chlorophyll across the Central Pacific compared with neutral conditions in June 2025. Chlorophyll is the pigment that helps plants absorbs sunlight to generate energy, and its reduction indicates a decline in phytoplankton, the base of the ocean’s food webs.
Hyung-Gyu Lim, an associate professor of oceanography at Chonnam National University in South Korea, told Mongabay by email that a developing El Niño can slow the process of upwelling, where nutrient-rich cold waters rise from the ocean depths to the surface. “This may trigger less nutrient supply. It is not surprising for me,” Lim said.
Matthew Kehrli and Graham Trolley, oceanographers at NASA’s Goddard Space Flight Center, wrote in a NASA Earth Observatory article that El Niño can suppress upwelling because easterly equatorial trade winds weaken, causing the warm surface layer of the ocean to extend deeper.
They added that as El Niño progresses, chlorophyll concentrations will likely decrease further over a broader region.
The ecological consequences of this nutrient decline would mean less food available for zooplankton, as well as for fish, seabirds, and marine mammals, the NASA Earth Observatory article said. This affects fisheries: Peru’s anchovy fisheries, for example, saw significant declines in catch during previous El Niño events, driven by warmer surface waters, reduced upwelling, and lower phytoplankton levels. This year, the country has repeatedly suspended its vital anchovy fishery to protect vulnerable fish stocks, while starving pelicans have begun invading urban ports in search of food.
NOAA’s Climate Prediction Center estimates a greater than 90% chance the current El Niño will persist into early 2027.
Despite the severe immediate disruptions, the NASA Earth Observatory said oceans often undergo a “chlorophyll rebound” once the event subsides.
Research led by Lim also suggests higher iron concentrations from ocean currents, as well as iron dust blown from dry land in parts of Central and South America, help fuel the resurgence of chlorophyll after El Niño. Iron is a key nutrient that stimulates phytoplankton growth.
Lim said recent Earth System Model studies “suggest that oceanic drivers facilitate a post-El Niño chlorophyll rebound fueled by subsurface iron supply. Furthermore, atmospheric drivers — such as dust-iron deposition — can significantly modulate marine productivity.”
Lim added surface satellite maps only show part of the ecological picture. To truly capture the dynamics, he said, advanced observation systems must integrate both surface and subsurface observations from oceans.
Banner image: Average chlorophyll concentrations in the Central Pacific for June 2026, right, appear significantly reduced under a strengthening El Niño compared to June 2025, when conditions were neutral. Images courtesy of NASA Earth Observatory/Michala Garrison.
