When the wind blows parallel to a coastline, surface waters are pushed offshore and water is drawn from below to replace the water that has been pushed away. The upward movement of this deep, colder water is called upwelling.
The deeper water that rises to the surface during upwelling is rich in nutrients. These nutrients “fertilize” surface waters, encouraging the growth of plant life, including phytoplankton. These phytoplankton serve as the ultimate energy base in the ocean for large animal populations higher in the food chain, providing food for fish, marine mammals, seabirds, and other critters.
Upwelling can also play an important role in the movement of marine animals. Most marine fish and invertebrates produce microscopic larvae which, depending on the species, may drift in the water for weeks or months as they develop. For adult marine creatures that live in shallow waters nearshore, upwelling that moves surface water offshore can potentially move drifting larvae long distances away from their natural habitat, thus reducing chances for survival. Thus, it will reduce the overall productivity by reducing the diversity of the region.
In some ways, upwelling can be a mixed blessing to coastal ecosystems. It can infuse coastal waters with critical nutrients that fuel dramatic productivity, but it can also rob coastal ecosystems of offspring required to replenish coastal populations.