Final answer:
The neritic zone is the marine zone rich in photosynthetic organisms like phytoplankton, which are critical for the oceanic food chain. This zone provides the right conditions for photosynthesis, supporting diverse marine life and serving as a primary area for fisheries.
Step-by-step explanation:
The zone with abundant life forms and photosynthetic organisms like phytoplankton as the base of marine food webs is the neritic zone. This zone extends from the intertidal zone to the depths of about 200 m (650 ft) at the edge of the continental shelf. Due to sunlight penetration, photosynthesis can occur in this well-oxygenated, low pressure, and stable temperature environment, making it rich in marine life and the primary area for the world's fisheries.
Specifically, the neritic zone is where phytoplankton and floating Sargassum create a habitat for various marine life such as zooplankton, protists, small fishes, and shrimp, forming the basis for the food chain. These photosynthetic organisms are crucial for the ecosystem as they perform a significant portion of the world's photosynthesis. Unlike the deep ocean zones where light does not reach and photosynthetic organisms are not found, the neritic zone is productive and supports a wide variety of organisms.