Why are phytoplankton, and not benthic algae or rooted aquatic plants, the dominant photosynthetic organisms of the oceanic pelagic zone? (See Figure 52.15.)

A photosynthetic organism is an organism that performs the process of photosynthesis.Plants, algae, and cyanobacteria are the only species capable of photosynthesis. Photoautotrophs produce their nourishment by using light, that is, sunlight.

Microalgae, or phytoplankton, are similar to terrestrial plants in that they possess chlorophyll and need sunlight to survive and grow.Phytoplankton is primarily buoyant and floats in the ocean's upper layers where sunlight enters the water.

They also need inorganic nutrients such as nitrates, phosphates, and sulfur, convertingthem into proteins, lipids, and carbohydrates.

The pelagic zone refers to the open sea area outside the coasts or on the sea bottom consisting of the water column.Oceans below the continental shelf are home to pelagic fish. The pelagic zone, where pelagic fish reside, gives them their name.

Plankton and a range of fish species live in the relatively shallow photic zone. However, the bulk of the ocean volume (the aphotic zone) is dark and contains no life because water absorbs light efficiently, and the ocean is deep