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Lesson Note
Subject: Biology
Topic: Aquatic Habitat

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

  1. Say the meaning of Estuarine habitat;
  2. State the characteristics of Estuarine habitats;
  3. State some adaptive features of the plants and animals to Estuarine habitat;
  4. Prepare a simple food chain of the organisms in Estuarine habitat;
  5. Mention the factors affecting Estuarine habitat.

Estuarine habitat is a body of water formed at the coast as a result of the action of tides which mix salt water from the sea with fresh water from the land. The mixing of salt water and fresh water results in the formation of a brackish water. This brackish water is what is called estuarine.

Types of Estuaries
Estuary is found in the following bodies of water

  1. Delta: A delta is where a river divides into many channels before entry into the ocean or sea. Brackish water or estuary (delta) is formed at the mouth of a river as it enters the sea.
  2. Lagoon: Lagoon is a body of ocean water that enters into the land through a canal and therefore has the opportunity of mixing with fresh water from rivers and streams.
  3. Bay: Bay is a little or small portion of the sea water which enters into the land and mixes up with fresh water from rivers and streams. It should be noted that a lagoon is bigger than a bay and it may be longer enough to join the sea at another end while bay is very small and not long enough to rejoin the sea in another end. Below is what they look like:

Characteristics of Estuarine Habitats
The followings are the characteristics of the estuarine habitats:

  1. Fluctuation in salinity: Salinity fluctuates in this habitat. Salinity is lower at the mouth of a river and gets higher towards the sea. Salinity is also affected by season. While rainy season reduces salinity due to addition of fresh water, dry season increases it.
  2. Turbidity: Turbidity of estuarine habitat increases especially during the rainy season when lots of debris are brought down by rivers to the habitat. This high turbidity also reduces the rate of photosynthesis and respiration by the organisms.
  3. Shallowness of water: Unlike the sea water which is deep, the water in estuarine habitat is very shallow.
  4. Low species diversity: The estuarine habitat has low diversity of species compared to marine habitat. Common plant species are phytoplanktons algae, marsh vegetation etc while animal species are crabs, oysters, lobsters, fishes etc.
  5. Water is affected by tides: Sea water usually flows rapidly into estuaries a high tides and rushes back into the ocean at low tides.
  6. High level of nutrients: The estuarine habitat contains abundant nutrients especially the organic detritus which form the bulk of producers in the habitat.
  7. Low Oxygen content: Oxygen content of estuarine habitat is generally very low and as a result, much of the microbiological activities are anaerobic.

Distribution of Plants and Animals In Estuarine Habitats

Examples of Plant Species and their Adaptive Features to Estuarine

  1. Planktons (diatoms): They possess air spaces in their tissucs, rhizoids or false feet for attachment to rock shores and air bladder for bouyancy.
  2. Algae: They possess chlorophyll for photosynthetic activities and small size or large surface area for floating.
  3. Red mangrove (Rhizophora racemosa): It has silt roots which grow down from the stem into the soft mud and develop numerous rootlets which have air spaces for conducting air to the tissues of the roots. The roots also provide support and do prevent plants from being washed away by the tides. Again the seeds of red mangrove germinate while they are still on the parent plant thereby preventing the seedlings from being carried away by water current.
  4. White mangrove (Avicennia nitida): It has pneumatophores or breathing roots for exchange of gases.

Examples of Animals Species and their Adaptive Features to Estuarine

  1. Mosquito larvae and pupae: These organisms possess breathing trumpets for gaseous exchange.
  2. Crabs: They can burrow fast into the mud against predators, strong waves or tides.
  3. Water snails and shrimps: These animals can burrow into the mud when the tide is going out, thus escaping the periodic dilution of its external medium.
  4. Worms: They have strong protective and impermeable covering against high salinity.
  5. Mud skippers: These animals have fins adapted for crawling when on land and for swimming when in water.
  6. Fishes: Fishes like Tilapia have fins for movement and swim bladder for bouyancy.

Food Chain In Estuarine Habitat
A typical food chain in an estuarine habitat may have up to three, four or five trophic levels. The phytoplanktons such as diatoms and detritus form the basic producers which support the food chain. Some examples of food chains in the estuarine habitat are:
a. Detritus > Worms >Snails > Birds.
b. Diatoms Shrimps > Fishes.
c. Phytoplanktons> branaclesfish> bird

Factors Affecting Estuarine Habitats
The factors which affect estuarine habitats are common to aquatic habitats and these include temperature, wind, relative humidity, light and pH.

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