There are really two basic types of aquatic zones, or biomes: marine and freshwater. These two biomes are divided even further into smaller zones. While the marine biome carries a higher salinity content than the freshwater biome, both biomes support a wide variety of plant and animal life.
The marine biome is subdivided into four zones (inter-tidal, pelagic, benthic, and abyssal) and the coral reefs. Freshwater regions, which only has a salt content of 1% or less, is divided into two zones (littoral and limnetic) and wetlands, rivers and streams, and estuaries, even though estuaries have a slightly higher salt content.
Despite the fact that the ocean covers the largest portion of this biome, it is the inter-tidal zone that connects the ocean to land. The animals and plants that inhabit there live on the bottom and on the seashore. Red mangrove and sea grape trees, eelgrass and sea lettuce are some of the most common plants that grow there. The animals that are supported by the inter-tidal zone include sea stars, crabs, Black Oystercatchers, and the great blue herons.
The pelagic zone extends farther away from land and is much closer to the middle of the ocean. The animals that inhabit this area are tuna, sharks, hatchet fish, giant squid, and any colorless and blind animals that can survive in the darkest regions. Since the bottom of the pelagic zone is extremely dark and sunlight cannot get through to support the average water plant, phytoplankton, diatoms, and dinoflagellates can exist by floating near the surface.
The benthic zone, also known as the deep sea zone, is mainly composed of sand, silt, and any decomposing organisms. If there are any animals living there, they are bottom feeders like starfish, anemones, sponges, and various micro-organisms.
The abyssal zone lays in the deepest part of the ocean where larger animals can roam. Many of these creatures are invertebrates, like sharks and whales, and some large fish. Some of the oddest fish found there is the coelacanth which was once thought to be extinct but recent evidence has found it in the Indian Ocean. There’s even some species of fish living there that glow in the dark.
The coral reefs lie in the warm shallow waters that envelopes some continents and the surrounding islands. Coral, itself, is a living organism made up of animals and algae tissues. Coral feeds on other plants using photosynthesis. This is done by using tentacles to catch micro-organisms to eat. Coral reefs do play host to a variety of other species such as starfish, octopi, and numerous mollusks.
The littoral zone lies closest to the shore and houses a warm, shallow environment for a variety of fauna and flora. Tiny crustaceans, flatworms, insect larvae, snails, frogs, and turtles can live in this region. These creatures provide food for birds, reptiles, and any other animal that inhabits the shoreline.
The limnetic zone is the open water near the surface of lakes and ponds. This area is home to a variety of phytoplankton, zooplankton, and freshwater fish like bass and lake trout.
Wetlands are full of still waters where the soil can be completely saturated or inundated only part of the time. They include marshes, glades, and swamps. Muskrats, Great Blue Herons, and Painted Turtles are some of the many animals that find living in marshes suitable for them. While living in a swamp is not a pleasant option for people, the Northern Waterthrush, beaver, muskrat, mink, and White-tail Deer love it there. There are some regions with a higher salinity that can house shrimp and shellfish. Some of the plants that can survive living in wetlands are sedges and pond lilies. Trees do not grow directly in wetlands, but the wetlands can help support them.
Because the water is colder in rivers and streams, they can support different fauna and flora than lakes and ponds. River trout, salmon, and some small scavengers such as crayfish love the cold, rapidly moving water. Rivers and streams do have warmer spots. It’s in these warmer areas that catfish, carp, and some other bottom feeders thrive. Floating weeds and algae live around submerged tree roots and rocks in these regions.
And, lastly, there are the estuaries. Although it is saltier than freshwater, it’s really the spot where freshwater and marine water merge. While each location can house different species of plant and animal life, New Zealand will used as an example. The types of plants that can survive in the estuaries of New Zealand are sea grass, mangroves, oioi, saltwort, and cordgrass. Mudworms, tunneling mud crabs, sand flounders, and mud probers are permanent fauna residents of these particular estuaries. Some animals will make estuaries their home, but there will be migrating animals that just stay there temporarily like godwits, plovers, and eels.