El Nino Is Reshaping Pacific Marine Food Webs

The 2026 El Nino is already changing marine life in the Pacific, with satellite measurements showing a substantial reduction in surface chlorophyll across part of the central equatorial ocean.

NASA Earth Observatory compared June 2025, when conditions were neutral, with June 2026 as El Nino strengthened. Data from the Ocean Color Instrument on the PACE satellite reveal lower chlorophyll concentrations around the equator north of New Zealand.

Why chlorophyll is important to marine life

Chlorophyll-a is the light-absorbing pigment found in most phytoplankton. Measuring it from space gives scientists an indicator of how much microscopic plant life is present near the ocean surface.

Phytoplankton form the foundation of many marine food webs. Zooplankton feed on them, and those organisms in turn support fish, seabirds and marine mammals. A sustained decline can therefore influence ecosystems and fisheries far beyond the microscopic plants captured in satellite data.

PACE measures different wavelengths of light reflected from the ocean. This allows researchers to study ocean colour and distinguish changes in biological activity over large areas that would be impossible to sample continuously from ships.

How El Nino reduces nutrient supply

During El Nino, easterly trade winds along the equatorial Pacific weaken. The warm surface layer extends deeper and suppresses the normal upwelling of cooler water from below.

That deeper water carries nutrients that fuel phytoplankton growth. When upwelling weakens, the sunlit surface can receive fewer nutrients even though water temperatures are higher. NASA oceanographers said the lower chlorophyll observed in the central Pacific is consistent with that process.

The scientists expect the contrast to become more pronounced if El Nino continues strengthening. The affected region could show a larger reduction, expand across a wider area or do both, depending on the behaviour of the trade winds.

NOAA's Climate Prediction Center has estimated a 97 percent chance that the event will last through early Northern Hemisphere spring 2027. Forecast probabilities can change with new observations, but the assessment indicates that researchers may have many more months of data to examine.

Fisheries can feel the effects

Past El Nino events have reduced anchovy catches off Peru as warmer surface water and weaker upwelling limited phytoplankton. Peru's Ministry of Production has repeatedly suspended fishing in 2026 to protect the country's main fishing resource.

Those actions illustrate how an ocean-climate pattern can reach coastal economies and food supplies. The effect is not identical in every location, and fishing outcomes also depend on management, species movement and local conditions.

NASA noted reports of pelicans moving into Peruvian ports and urban areas in search of food. Such observations are consistent with stress in the food web, although individual animal behaviour should not be attributed to one cause without supporting ecological evidence.

PACE offers a new view of the event

The PACE mission launched in February 2024, making the 2026 event the first complete El Nino it can observe with global, near-daily hyperspectral measurements. Scientists can use the expanded range of wavelengths to study how particular phytoplankton communities respond, rather than relying only on a broad chlorophyll total.

The satellite also measures land vegetation pigments, clouds and aerosols, giving researchers opportunities to connect ocean changes with the wider climate system.

Marine ecosystems can rebound after El Nino. Studies have found higher-than-normal chlorophyll after some events, potentially supported by iron delivered through ocean currents and dust. A later La Nina can also increase nutrient upwelling and phytoplankton growth.

Continued observation will show whether the lower-chlorophyll zone expands and how quickly marine communities respond. For now, the latest satellite maps show an early ecological signal: the physical changes associated with El Nino are reducing productivity in part of the Pacific, and those effects can travel upward through the food web.