Final answer:
An estuary is the biome where a river meets the sea, creating brackish water and a habitat for young aquatic species. Photosynthetic organisms thrive in areas where sunlight penetrates, such as the photic, intertidal, neritic, and oceanic zones.
Step-by-step explanation:
The place where a river meets the sea is known as an estuary. Estuaries are unique biomes characterized by the mixing of fresh water from rivers and salt water from the sea, resulting in brackish water. They are crucial environments that offer protected areas for the early life stages of various species such as crustaceans, mollusks, and fish. Photosynthesis is a process that requires light and occurs primarily in areas where sunlight can penetrate the water. Considering the zones of the ocean, photosynthetic organisms are found in areas like the photic zone (where sunlight reaches), the intertidal zone (the area between the high and low tide lines), the neritic zone (the coastal part over the continental shelf), and the oceanic zone (the open sea beyond the edge of the continental shelf).