Marine Biomes

Marine biomes are aquatic biomes found in the salt water of the ocean. Major marine biomes are neritic, oceanic, and benthic biomes. Other marine biomes include intertidal zones, estuaries, and coral reefs.

Neritic Biomes

• Neritic biomesoccur in ocean water over the continental shelf.
• They extend from the low-tide water line to the edge of the continental shelf.
• The water here is shallow, so there is enough sunlight for photosynthesis.
• The water is also rich in nutrients, which are washed into the water from the nearby land.
• Because of these favorable conditions, large populations of phytoplankton live in neritic biomes.
• They produce enough food to support many other organisms, including both zooplankton and nekton.
• As a result, neritic biomes have relatively great biomass and biodiversity.
• They are occupied by many species of invertebrates and fish. In fact, most of the world’s major saltwater fishing areas are in neritic biomes.

 Oceanic Biomes

• Oceanic biomes occur in the open ocean beyond the continental shelf.
• There are lower concentrations of dissolved nutrients away from shore, so the oceanic zone has a lower density of organisms than the neritic zone.
• The oceanic zone is divided into additional zones based on water depth (see above Figure).

1. 1. The epipelagic zoneis the top 200 meters of water, or the depth to which enough sunlight can penetrate for photosynthesis. Most open ocean organisms are concentrated in this zone, including both plankton and nekton.
   2. The mesopelagic zone is between 200 and 1,000 meters below sea level. Some sunlight penetrates to this depth but not enough for photosynthesis. Organisms in this zone consume food drifting down from the epipelagic zone, or they prey upon other organisms in their own zone. Some organisms are detrivores, which consume dead organisms and organic debris that also drift down through the water.
   3. The bathypelagic zoneis between 1,000 and 4,000 meters below sea level. No sunlight penetrates below 1,000 meters, so this zone is completely dark. Most organisms in this zone either consume dead organisms drifting down from above or prey upon other animals in their own zone. There are fewer organisms and less biomass here than in higher zones. Some animals are bioluminescent, which means they can give off light . This is an adaptation to the total darkness.
   4. The abyssopelagic zone is between 4,000 and 6,000 meters below sea level.
   5. The hadopelagic zoneis found in the water of deep ocean trenches below 6,000 meters. Both of these zones are similar to the bathypelagic zone in being completely dark. They have even lower biomass and species diversity.

Benthic Biomes

• Benthic biomesoccur on the bottom of the ocean where benthos live.
• Some benthos, including sponges, are sessile, or unable to move, and live attached to the ocean floor.
• Other benthos, including clams, burrow into sediments on the ocean floor.
• The benthic zone can be divided into additional zones based on how far below sea level the ocean floor is (see above Figure).

1. • The sublittoral zoneis the part of the ocean floor that makes up the continental shelf near the shoreline. The water is shallow enough for sunlight to penetrate down to the ocean floor. Therefore, photosynthetic producers such as seaweed can grow on the ocean floor in this zone. The littoral zone is rich in marine life.
   • The bathyal zone is the part of the ocean floor that makes up the continental slope. It ranges from about 1,000 to 4,000 meters below sea level. The bathyal zone contains no producers because it is too far below the surface for sunlight to penetrate. Although consumers and decomposers live in this zone, there are fewer organisms here than in the sublittoral zone.
   • The abyssal zone is the part of the ocean floor in the deep open ocean. It varies from about 4,000 to 6,000 meters below sea level. Organisms that live on the ocean floor in this zone must be able to withstand extreme water pressure, continuous cold, and scarcity of nutrients. Many of the organisms sift through sediments on the ocean floor for food or dead organisms.
   • The hadal zoneis the ocean floor below 6,000 meters in deep ocean trenches. The only places where organisms are known to live in this zone are at hydrothermal vents, where invertebrates such as tubeworms and clams are found. They depend on microscopic archaea organisms for food. These tiny chemosynthetic producers obtain energy from chemicals leaving the vents.

Intertidal Zone

• The intertidal zoneis a narrow strip along the coastline that falls between high- and lowtide water lines.
• It is also called the littoral zone.
• A dominant feature of this zone is the regular movement of the tides in and out.
• In most areas, this occurs twice a day.
• Due to the tides, this zone alternates between being under water at high tide and being exposed to the air at low tide.
• The high tide repeatedly brings in coastal water with its rich load of dissolved nutrients.
• There is also plenty of sunlight for photosynthesis.
• In addition, the shallow water keeps large predators, such as whales and big fish, out of the intertidal zone.
• As a result, the intertidal zone has a high density of living things.
• Seaweeds and algae are numerous, and they support many consumer species, either directly or indirectly, including barnacles, sea stars, and crabs.
• Other conditions in the intertidal zone are less favorable. For example, there are frequent shifts from a water to an air environment. There are also repeated changes in temperature and salinity (salt concentration). These changing conditions pose serious challenges to marine organisms. The moving water poses yet another challenge.
• Organisms must have some way to prevent being washed out to sea with the tides. Barnacles cement themselves to rocks. Seaweeds have rootlike structures, called holdfasts, which anchor them to rocks. Crabs burrow underground to avoid being washed out with the tides.