How do cold, deep water upwellings increase organisms in an area?

Upwelling is a process in which currents bring deep, cold water to the surface of the ocean. Upwelling is a result of winds and the rotation of the Earth. There are many reason's how could deep water upwelling increase organisms in an area, here are a few:

Biodiversity and productivity

Because the deep water brought to the surface is often rich in nutrients, coastal upwelling supports the growth of seaweed and plankton. These, in turn, provide food for fish, marine mammals, and birds.

Upwelling generates some of the world's most fertile ecosystems. A 25,900-square-kilometer (10,000-square-mile) region off the west coast of Peru, for example, undergoes continual coastal upwelling and is among the richest fishing grounds in the world. Overall, coastal upwelling regions only cover 1 percent of the total area of the world's oceans, but they provide about 50 percent of the fish harvest brought back to shore by the world's fisheries.

During El Niño, a weather phenomenon that typically occurs every three to seven years, the Pacific Ocean's climate changes dramatically. The transition zone between warm surface water and cold deep water deepens. Trade winds are also weak during El Niño. The combination of weak winds and deeper water limits upwelling. The reduction in nutrient-rich water leads to a lower fish population in the area, and therefore to a smaller fish crop.

Animal movement
Upwelling affects the movement of animal life in the area. Tiny larvae---the developing forms of many fish and invertebrates---can drift around in ocean currents for long periods of time. A strong upwelling event can wash the larvae far offshore, endangering their survival.

Coastal climate
The cold water welling up to the surface cools the air in the region. This promotes the development of sea fog. The city of San Francisco, California, is famous for its chilly, foggy summers, brought on by seasonal upwelling in the area.