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Lesson Note
Subject: Biology
Topic: Aquatic Habitat

Subtopic: Marine Habitat
Lesson Objectives: At the end of the lesson, learners should be able to:

  1. Say the meaning of marine habitat;
  2. Describe the characteristics of marine habitats;
  3. Describe the pattern or zone of distribution of plants and animals in marine habitat, noting the dominant ones;
  4. Recognise some adaptive features of the plants and animals in the habitats;
  5. Infer the food chain of the organisms;
  6. Determine some of the physical factors affecting marine habitat.

Lesson Summary/Discussion

Definition of Aquatic Habitat
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 and plants.

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 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 features or characteristics:

  • 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 salt by weight per 1000 parts of water.
  • 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. Therefore, the density of ocean water is higher than that of fresh water.
  • 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.
  • Waves: Waves are movement of surface of 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.
  • Light penetration: Light penetrates the an 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.
  • Size: Marine habitats represent 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, Indian ocean, Pacific ocean (the largest) etc.
  • Hydrogen ion concentration: Salt water is known to be alkaline in nature with pH of about 8.0-9.0 near the surface.
  • 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.
  • 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.
  • 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.

Major Zones of the Marine Habitat

  1. 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 waves break at the shore.
  2. 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.
  3. Litoral or Subtidal zone: This zone is about 200m deep. It is constantly under water., it has abundant sunlight and therefore abundant nutrients.
  4. Benthic zone: Benthic zone is also under water and is about 50Om deep. It has low light penetration and low nutrients.
  5. 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.
  6. 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.
  • a. Euphoticzone: 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.
  • b. Disphotic Zone: This is a region of dim light. Consumers and decomposers are found there also. Light penetrates the water but the intensity is too low for photosynthesis to occur.
  • c.Aphotic zone: This represents the bottom or bed of the seas and oceans. It is characterised by cold dark water without light penetration and very few living organisms are found in this zone

Distribution of Organisms in Marine Habitats and their Adaptive Features
The organisms in marine habitats include plants and animals.

General Adaptation of Plants in Marine or Salt Water Swamps

  1. Plants posses succulent stem or roots or store water to dilute the salt.
  2. Presence of pneumatophores or breathing roots for breathing atmospheric air or oxygen.
  3. Presence of stilt roots for anchorage.
  4. Presence ofvivi parous seedling to ensure their survival or continuity.
  5. Some secrete excess salt into swamps to maintain balance of body salt.

Examples of Plants in Marine Habitat and their Adaptive Features

  1. 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 bouyancy.
  2. Algae, e.g. sargassum: Algae possess chlorophyll for photosynthetic activities, small size or large surface area for drifting or floating
  3. Sesuvium: Sesuvium possesses thick leaves or reduced leaves for water conservation.
  4. Planktons, e.g. diatoms: They possess air spaces in their tissues, rhizoids (fake feet) for attachment to rocks and air bladder for buoyancy.

Examples of Animals in Marine Habitats and their Adaptive Features

  1. 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.
  2. Cartilagenous fishes: Cartilagenous fishes like shark and dogfish have the 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 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.
  4. Shrimps: They possess powerful claws or chelipods for seizing or holding food or prey.
  5. Crabs: Crabs are capable of burrowing fast into the mud to protect them against predators, strong waves or tides.
  6. Periwinkles: They possess lungs for breathing and foot for attachment.
  7. Starfish: They possess tube feet which enable them to hold on to rock shores, and hard shell which prevents dessication or drying up.

Food Chain in Marine Habitat
A typical food chain in marine habitat 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 are illustrated below:

Factors Affecting Marine Habitats
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 habitat which has been discussed earlier at the beginning of this lesson. kindly scroll back up for details.

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