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Why does upwelling make some ocean regions highly productive for fisheries?

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Diagram showing ocean zonation by depth and region, with labeled layers: littoral, sublittoral, bathyal, abyssal, and hadal along the seafloor, and epipelagic, mesopelagic, bathypelagic, and abyssalpelagic in open water. The littoral zone is at the high-tide mark. Vertical scale marks photic and aphotic zones from surface to 10,000 meters. — Marine ecosystem Zonation of the ocean. Note that in the littoral zone the water is at the high-tide mark.

Upwelling is a critical process that drives high biological productivity in marine ecosystems by transporting nutrient-rich water from the depths toward the surface.1

This influx of nutrients creates an ideal environment for phytoplankton to reproduce rapidly through photosynthesis, as they utilize these nutrients alongside solar energy. This surge in phytoplankton supports a robust food web: grazing zooplankton multiply in response to the abundant food supply, which in turn provides essential nourishment for nekton, including the fish populations that sustain major fisheries.12

Regions such as the waters off Peru, California, and the west coast of southern Africa are among the most productive in the world precisely because of these nutrient-replenishing currents. When upwelling is disrupted—often by shifts in atmospheric circulation like El Niño—the resulting lack of nutrients can lead to the collapse of these vital fisheries.12