The ocean can be divided into many zones, each with its own dominant organisms. The bottom of the ocean is known as the benthic zone, while the pelagic zone extends from the ocean floor to the surface. It is divided according to its proximity to land and the depth of water. The neritic zone is that part of the pelagic zone which extends from the high tide line to the ocean bottom less than 200 m deep while water deeper than 200 m feet is referred to as the oceanic zone.

The neritic zone can be partitioned based on tide levels. The upper band is known as the intertidal zone, encompassing the region from the wave splash zone to the low tide mark. The highest zone within the intertidal is known as the supralittoral zone and is the area above the high tide mark that receives only wave splash and sea-water mist. Some terrestrial organisms live here, such as saltwater-tolerant lichens. Below the supralittoral zone is the supralittoral fringe, or "splash zone", which receives a regular splashing from waves at high tide. The next zone is the midlittoral zone, which includes the majority of the intertidal zone and recieves periodic exposure and submersion by tides. The lowest zone, the infralittoral zone, includes the lowest levels exposed by extreme spring tides and extends into the subtidal zone, marking the beginning of the marine environment.

The oceanic zone is subdivided into the epipelagic, mesopelagic, and bathypelagic zones. The epipelagic (euphotic) zone receives enough sunlight to support photosynthesis. The mesopelagic (disphotic) zone, where only small amounts of light penetrate, lies below and while 90% of the ocean lies in the bathypelagic (aphotic) zone into which no light penetrates.