Classwork Series and Exercises {Biology – SS2}: Aquatic Habitat

Biology SS 2 Week 3

Topic: Aquatic Habitat

Introduction

Aquatic habitat is a body of water in which certain organisms live naturally. In other words, aquatic habitats are habitats or places that relates to lives in water. Organisms that live in water are called aquatic organisms. Examples of aquatic organisms are fish, crabs, toads, plants etc.

Types of Aquatic Habitats

There are three types of aquatic habitats. These are marine or salt water habitats, estuarine or brackish water habitats and fresh water habitats

MARINE HABITATS

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

Characteristics of Marine Habitat

The marine or salt water habitat has the following characteristics:

1. Salinity: Salinity is defined as 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.
2. Density: 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.
3. Pressure: 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 atmosphere 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.
4. Size: Marine habitats represent the largest of all the habitats. The ocean alone occupies over 70% or 360 million square kilometers of the earth’s total area of 510 million square kilometers. Examples of oceans are Atlantic ocean, Indian ocean, Pacific ocean (the largest)
5. Currents: 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: 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.
7. Oxygen concentration: The concentration of oxygen in the ocean is highest at the surface while it decreases with depth, and in the very deep parts of the oceans there is practically no oxygen.
8. Hydrogen ion concentration: Salt water is known to be alkaline in nature with pH of about 8.0-0.9 near the surface.
9. Waves: Waves are movement of surface waters of the oceans and it can take any direction and are caused by winds. Waves bring about the mixing of sea water especially on the surface of the ocean.
10. Light penetration: Light penetrate 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 turbidity.

Major Zones of the Marine Habitats

 

The major ecological zones of the marine habitats include:

The two major marine provinces: the benthonic (bottom) and the pelagic (water column).

• The benthonic environment is divided by depth into the:
  Littoral zone                  Inter tidal zone
  Sublittoral zone,                 0 to 200m     (continental shelf)
  Bathyal zone,                 200 to 2000m    (shelf wall)
  Abyssal zone,              2000 to 6000m    (abyssal plains)
  Hadal zone.                          >  6000m    (deep sea trenches)
• The pelagic environment is divided into the:Neritic Zone       (water over the continental shelf, no sub divisions)
  Oceanic Zone.  (water beyond the shelf break, deep ocean water)

Because of the range in depths, the oceanic zone is subdivided further into the:

• Epipelagic                 0     to  200m
• Mesopelagic         200     to  1000m
• Bathypalagic       1000m  to  2000m
• Abyssalpelagic   2000m   to  6000m
• Hadelpelagic                    >  6000m

The oceanic zone can also be divided into different zones based upon depth of light penetration.

• The photic zone is the depth where light is sufficient for photosynthesis during the day.    ( 0 to 100m)
• The dysphotic zone (twilight zone) is where illumination is too weak for photosynthesis.   (100 to 450m approx)

The aphotic zone receives no light from the surface because it is all absorbed by the water above. ( > 450m)

Distribution of Organisms in Marine Habitats and their Adaptive Features

The organisms in marine habitats include plants and animals

Plants in Marine Habitat

• Sea weeds: They possess hold-fast for attachment. They also possess mucilagenous cover to prevent dissociation. They have divided leaves, floating devices or air bladder for buoyancy.
• Algae, e.g. sargassus: Algae possess chlorophyll for photosynthesis activities, small size or large surface area for drifting or floating
• Sesuvium: Sesuvium possesses thick leaves or reduced leaves for water conservation
• Planktons, e.g. diatoms: They possess air spaces in their tissues, rhizoids (fake feet) for attachment to rocks and air bladder for buoyancy

Animals in Marine Habitats and their Adaptive Features

Barnacles: Barnacles have protective mantle or pad for attachment or anchorage to rock shore, cilia for feeding, shell which prevents dessication and mantle which retains water.

Cartilaginous fishes: Cartilaginous fishes like shark and dogfish have the ability to retain urea in their body to cope with high salinity

Bony fish: Fishes like tilapia and herring drink salt water to cope with high salt content of the ocean. They also possess salt secreting glands in their gills or eyes to enable them maintain osmoregulation or salt balance

Shrimps: They possess powerful claws or chelipods for seizing or holding food or prey.

Crabs: Crabs are capable of burrowing fast into the mud to protect them against predators, strong waves or tides

Periwinkles: They possess lungs for breathing and foot for attachment

Starfish: They possess tube feet which enable them to hold on to rock shores, and hard shell which prevents dessication or drying up

Factors Affecting Marine Habitats

Some of the major factors affecting marine habitats are:

Temperature

Sunlight

Wind

Density

pH

Salinity