The neritic zone is the portion of the world's oceans stretching from the edge of the intertidal zone to approximately the edge of the continental shelf. It forms part of the epipelagic zone, the 200 meters closest to the surface, which is also known as the sunlight zone. Accordingly, this is the province of the ocean most full of life. Yet the life here is heavily influenced by the abiotic factors present — that is, the factors that influence the diversity and quantity of life in an ecosystem that are themselves nonbiological or nonliving.
Sunlight is key in nearly all ecosystems of the earth. This is certainly true for the neritic zone — it forms part of the epipelagic zone. This zone's boundary is approximately the so-called compensation depth, the lowest depth at which photosynthesis can take place in sufficient quantity, generating enough energy to sustain life. Thus the presence of sufficient sunlight in the neritic zone is an important abiotic factor in the quantity and diversity of life that the zone supports.
Because the neritic zone has close contact with the tidal region and its own seafloor, the water of this zone is much richer in minerals and other nutrients that support life than the waters of the ocean beyond the edge of the continental shelf. A number of specific elements are essential for life, among them nitrogen, phosphorus, calcium and silicon. These elements are extracted almost exclusively from the soil in land-based ecosystems. These and other relatively insoluble elements important to life, such as iron, copper, magnesium and zinc, are thus heavily recycled in ocean ecosystems. Because of the neritic zone's closer association with the crust, which carries such nutrients, it is easier to maintain life in this environment.
The reaction rate of all chemical reactions is heavily influenced by the temperature at which they occur. Reactions are speeded up when temperatures are higher; reactions are slowed down at lower temperatures. A temperature increase of only 10 degrees Celsius will double a reaction's rate! The neritic zone is the warmest zone in the ocean because of its relatively shallow depth, giving it more heat input from the sun per unit of water compared with the rest of the ocean. Thus life can carry on its necessary chemistry most efficiently here.
A number of different gases are important to sustain life, among them oxygen. Oxygen is required for the last and most efficient step in cellular respiration, known as oxidative phosphorylation. Because of the neritic zone's close contact with the atmosphere, levels of dissolved atmospheric gases such as oxygen and carbon dioxide in the seawater are much higher than in nonepipelagic zones of the ocean. These gases can thus more readily be harnessed for respiration and photosynthesis — making the processes of life happen more readily.
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