The aquatic biome is definitely the largest biome out there. The aquatic biome, estuary, oceans, lakes, rivers, ponds, coral reefs. Aquatic regions house numerous species of plants and animals, both large and small. The aquatic biome can be broken down into two basic regions, freshwater (i.e, ponds and rivers) and marine (i.e, oceans and estuaries).
Let's start with standing freshwater biomes, from a river to a lake or pond. The water doesn't move very quickly here. Water is the common link among the five biomes and it makes up the largest part of the biosphere, covering nearly 75% of the Earth's surface Scientists divide lakes into two major levels, limnetic (the top), and profundal (the deeper part). They even have names for the shore (littoral) and the very bottom on the floor of the lake (benthic).
Scientists break this biome into three layers. At the surface is the euophotic zone. There is a large amount of sunlight and oxygen but very few nutrients. They all fall to the bottom of the ocean. You'll find many small organisms that are photosynthetic. As we move down, we get to the bathyal zone. The light is very dim. No little organisms are found here, just some fish who feed on the organisms at the surface. At the bottom of the ocean is the abyssal zone. This zone is pitch black, with no producers, little oxygen, extremely cold, and high pressure. There are living organisms down there. They usually feed on the dead stuff that falls from the surface layers. Then, of course, there are the predators that swim through the murky depths.