The correct answer is: B. photic
The photic zone is the depth of a water body that receives enough sunlight for photosynthesis to occur. It is typically defined as the depth at which light can penetrate to a depth of 1% of its surface value. The photic zone is important for aquatic ecosystems because it is where most of the primary production occurs. Primary production is the process by which plants use sunlight to convert carbon dioxide and water into organic matter. This organic matter is then used by other organisms in the food chain.
The photic zone is typically divided into two subzones: the euphotic zone and the aphotic zone. The euphotic zone is the uppermost layer of the photic zone, where there is enough light for photosynthesis to occur. The aphotic zone is the lowermost layer of the photic zone, where there is not enough light for photosynthesis to occur.
The euphotic zone is typically much shallower than the aphotic zone. The depth of the euphotic zone varies depending on the clarity of the water and the latitude. In clear water, the euphotic zone can extend to depths of over 100 meters. In turbid water, the euphotic zone may be only a few meters deep. The depth of the euphotic zone also decreases with increasing latitude. This is because the angle of the sun’s rays is lower at higher latitudes, which means that less light reaches the surface of the water.
The photic zone is an important part of aquatic ecosystems. It is where most of the primary production occurs, and it is home to a variety of organisms. The photic zone is also important for human activities, such as fishing and aquaculture.