Phytoplankton are very small single cell plants which float in the water and play a key role in the marine food chain. As the main primary producer they convert sunlight, carbon dioxide and nutrients into carbohydrates on which nearly all life in the ocean - including shrimps, fish and whales - depend.

In most parts of the Earth's ocean, phytoplankton concentration is extremely low. However, in "upwelling areas", deep water is pumped up to the surface by strong winds, such as trade winds blowing parallel to the coast. This deep water is rich in nutrients and as this supplies phytoplankton with the nitrogen, phosphate and silicate they need for their growth, this process supports the whole food chain.

The most important fishing grounds can be found in upwelling areas. When this upwelling process collapses, as for instance off the Peruvian coast during El Nino events, the ecosystem is dramatically perturbed. Climate change has an impact on the intensity and geographical position of upwelling areas, which in turn has important consequences on fishing industries thus affecting the livelihoods of the local people.