Reasons that the deep ocean is a difficult environment for organisms include the

Ocean Zones     To better understand regions of the ocean, scientists define ocean zones based on depth of water or distance from shore. By depth of water, the entire ocean is divided into two major zones: the photic zone and the aphotic zone.     - The photic zone consists of the top 200 meters of ocean water. This is the depth to which sunlight can penetrate ocean water. Organisms that photosynthesize depend on sunlight for food, so they are restricted to the photic zone. Tiny photosynthetic organisms known as phytoplankton supply nearly all of the energy and nutrients to the rest of the... Show more

Ocean Zones    
To better understand regions of the ocean, scientists define ocean zones based on depth of water or distance from shore. By depth of water, the entire ocean is divided into two major zones: the photic zone and the aphotic zone.    
- The photic zone consists of the top 200 meters of ocean water. This is the depth to which sunlight can penetrate ocean water. Organisms that photosynthesize depend on sunlight for food, so they are restricted to the photic zone. Tiny photosynthetic organisms known as phytoplankton supply nearly all of the energy and nutrients to the rest of the marine food web. Therefore, most other marine organisms live in, or at least visit, the photic zone.    
- The aphotic zone includes all ocean water below the top 200 meters. In the aphotic zone, there is not enough sunlight for photosynthesis. The aphotic zone makes up the majority of the ocean. However, it contains a relatively small proportion of its organisms, both in diversity and in numbers.    

By distance from shore, the ocean is divided into three major zones: the littoral, neritic, and oceanic zones.    
- The littoral, or intertidal, zone is closest to shore. It comprises the region between high and low tide marks.    
This zone is characterized by constant change, as the tides rise and fall and ocean waves crash on shore. By depth of water, the entire littoral zone is in the photic zone.    
- The neritic zone extends from the low tide mark to the edge of the seaward side of the continental shelf. By depth, some of this zone is in the photic zone, and some of it is in the aphotic zone.    
- The oceanic zone is the rest of the ocean beyond the continental shelf. The top part of the oceanic zone is in the photic zone, but the vast majority of it is not.    

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