In the ocean, communities of plants, algae, and animals are distributed according to the depth of the water and distance from shore. Light reaches organisms in the photic zone, where microscopic phytoplankton and multicellular algae provide food for the animal community. Light levels in the aphotic zone are too low to support photosynthesis. The seafloor is called the benthic realm. Fishes and marine mammals swim in open water known as the pelagic realm. A distinctive biome called a(n) estuary is found where a freshwater stream or river merges with the ocean.