Some of the world's most important commercial fisheries are on the continental shelves, including the North and Barents Seas of western Europe, the Grand Banks and other shallow waters of northeastern North America, the Gulf of Mexico, and inshore waters of much of western North America. In certain regions of the ocean, conditions make possible upwellings to the surface of relatively deep, nutrient-rich waters. Because of the increased nutrient supply, upwelling areas are relatively fertile, and they support sizeable populations of animals, including large species of fishes and sharks, marine mammals, and seabirds. Some of Earth's most productive fisheries occur in upwelling areas, such as those off the west coast of Peru and other parts of South America and large regions of the Antarctic Ocean. An estuary is a region along a coastline where a river empties into the ocean.
Estuaries display characteristics of both marine and freshwater biomes.
They typically have substantial inflows of freshwater from the nearby land, along with large fluctuations of saltwater resulting from tidal cycles. Examples of estuaries include coastal bays, sounds, river mouths, salt marshes, and tropical mangrove forests. Because the nutrients carried into them by rivers, estuaries are highly productive ecosystems. They provide important habitats for juvenile stages of many species of fish, shellfish, and crustaceans that are later harvested for food. The seashore biome is formed where the land meets the ocean.