Aquatic habitat and it\’s features

Aquatic habitat and its functions, WHAT IS AQUATIC HABITAT this is a body of water in which certain organisms live naturally.

In other words, aquatic habitats are habitats or places that relate to lives in water.
Organisms that live in water are called aquatic organisms. Examples of aquatic organisms are fish, crabs, toads and plants.

Types of aquatic habitat

There are three types of aquatic habitats. These are:
1. Marine or salt water habitats.
2. Estuarine or brackish water habitats.
3. Fresh water habitats.



Marine habitats refer to aquatic habitats which contain salt water. Marine habitats include the oceans, lakes, shores and the open seas.


The marine or saltwater habitat has the following characteristics:

Salinity of marine habitat:

salinity is the degree of saltiness or concentration of salt solution in oceans.

The marine habitats have a high salinity and its average salinity is put at 35.2 per 1000. In other words, the average salinity of the ocean is 35.2 parts of salts by weight per 1000 parts of water.

The density of the world\’s aquatic habitat:

the density of marine water is high, hence many organisms can float in it. While the density of ocean water is about 1.028, that of fresh water is 1.00. So, the density of ocean water is higher than that of fresh water.

water pressure increases in depth at the rate of one atmosphere for every ten metres. In other words, pressure varies from one atmosphere at the surface level to about 1000 atmospheres at the greatest depth.

This is why animals in marine habitats have features which enable them to adapt especially at the deep level of the sea.

Size of the world\’s aquatic habitat:

marine habitats represents the largest of all the habitats. The ocean alone occupies over 70% or 360 million square kilometres of the earth’s total area of 510 million square kilometres.

Examples of oceans are Atlantic Ocean, Pacific Ocean, (the largest), Indian Ocean etc.

Currents of aquatic habitat
currents are always produced by wind at the surface of the ocean. Currents are also produced down the ocean as a result of certain variations such as salinity and changes in temperature.
6. Tides of aquatic habitat-tides are the alternate rise and fall of the surface of the ocean approximately twice a day.
This alternate rise and fall in water level is due to the gravitational effects of the moon and sun. read about the water cycle here and see the impact of it on the ocean tides

Oxygen concentration in Aquatic habitat:

the concentration of oxygen in the ocean is the highest at the surface while it decreases with depth, and in every deep part of the ocean, there is practically no oxygen.

Hydrogen ion concentration:

salt water is known to be alkaline in nature with pH of about 8.0-9.0 near the surface.

Waves of aquatic habitat:

waves are movement of surface waters of the oceans and they can take any direction and are caused by winds. Waves bring about the mixing of seawater, especially on the surface of the ocean.

10. Light penetration: light penetrates the ocean water only to a maximum depth of 200 metres. Therefore, plant life is limited to the upper layers of the ocean where light can penetrate. Penetration of light depends on the water\’s turgidity.


major ecological zones of the marine habitats include:

Supratidal or splash zone:

this is the exposed zone of the marine habitat. It has occasional moisture since it is the area where water splashes when the wave break at the shore.

Intertidal or neritic zone:

this zone which is also called planktonic or euphotic zone is only exposed at low tide or covered by water at high tide. It has high photosynthetic activities because of abundant sunlight. There is also fluctuation of the water temperature.

Littoral or sub-tidal zone:

this zone is about 200m deep. It is constantly under water, it has abundant sunlight and therefore abundant nutrients.

Benthic zone:

benthic zone is also underwater and is about 500m deep. It has low light penetration and low nutrients.

Pelagic or abyssal zone:

this zone is about 7000m deep. It has low temperature, low light penetration, high pressure, low photosynthetic activities and the primary production of food is by chemosynthesis.

Hadal or aphotic zone:

this is the deepest zone of the marine habitat. It is over 7000m deep. It forms the floor or bed of the ocean. There is no light penetration and no photosynthetic activities.

On the basis of depth or light penetration or vertical zoning of marine habitat, there exist three major zones.

These are euphotic, disphotic and aphotic zones.

Euphotic zone:

this is an area which is directly connected with sunshine. Producers, consumers and decomposers are present here. There is enough light penetration for photosynthesis to take place.

Disphotic zone:

this is a region of dim light. Consumers and decomposers are also found there. Light penetrates water but the intensity is too low for photosynthesis to take place.

iii. Aphotic zone:

this represents the bottom or bed of the seas and oceans. It is characterized by cold dark water without light penetration and very few living organisms are found in this zone.


The organisms in marine habitats include plants and animals


  1. Seaweeds: they possess hold-fast for attachment. They also possess mucilaginous cover to prevent dissociation. They have divided leaves, floating devices or air bladders for buoyancy.
  2. Algae, e.g. sargassum: algae possess chlorophyll for photosynthetic activities, small size or large surface area for drifting or floating.
  1. Sesuvium: Sesuvium possesses thick leaves or reduced leaves for water conservation.
  2. Planktons, e.g. diatoms: possess air spaces in their tissues, rhizoids (fake feet) for attachment to rocks and air bladder for buoyancy.


  1. Barnacles: barnacles have protective mantle or pad for attachment or anchorage to rock shore, cilia for feeding, shell which prevents desiccation and mantle which retains water.
  2. Cartilaginous fishes: cartilaginous fishes like shark and dog fish have ability to retain urea in their body to cope with high salinity.
  3. Bony fish: fishes like tilapia and herring drink salt water to cope with the high salt content of the ocean. They also possess salt-secreting glands in their gills or eyes to enable them to maintain osmoregulation or salt balance.
  1. Shrimps: they possess powerful claws or chelipeds for seizing or holding food or prey.
  2. Crabs: crabs are capable of burrowing fast into the mud to protect them against predators, strong waves or tides.
  1. Periwinkles: they possess lungs for breathing and foot for attachment.
  2. Starfish: they possess tube feet which enable them to hold on to rocky shores and a hard shell which prevents desiccation or drying up.


A typical food chain in marine habitats could be up to three or four trophic levels. The phytoplanktons, e.g. diatoms serve as the major producers which support the food chain. Some examples of food chain

i. Diatoms==Zooplanktons==Tilapia==Shark
ii. Diatoms==Crabs==Tilapia


Some of the major factors affecting marine habitats are temperature, sunlight, wind, density, pH and salinity. These factors have been explained under the characteristics of marine habitats.

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