Classwork Series and Exercises {Biology SS2}: Estuarine Habitats

Biology SS 2 Week 4

Topic: Estuarine Habitats

Introduction

 

Estuarine habitat is a body of water formed at the coast as a result of the action of tides which mix salt water from 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

• 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
• 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
• 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 long enough to join the sea at another end while bay is very small and not long enough to rejoin the sea in another end

Characteristics of Estuarine Habitats

The followings are the characteristics of the estuarine habitats:

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.

Turbidity: Turbidity of estuarine habitat increases especially during the rainy season when lots of debris is brought down by rivers to the habitat. This high turbidity also reduces the rate of photosynthesis and respiration by organisms

Shallowness of water: Unlike the sea water which is deep, the water in estuarine habitat is very shallow

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.

Water is affected by tides: Sea water usually flows rapidly into estuaries at high tides and rushes back into the ocean at low tides

High level of nutrients: The estuarine habitat contains abundant nutrients especially the organic detritus which form the bulk of producers in the habitat

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

Plant Species and their Adaptive Features

Planktons (Diatoms): They possess air spaces in their tissues, rhizoids or false feet for attachment to rock shores and air bladder for buoyancy

Algae: They possess chlorophyll for photosynthetic activities and small size or large surface area for floating

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 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

White mangrove (Avicennia nitida): It has pneumatophores or breathing roots for exchange of gases

Animals species and their Adaptive Features

Mosquito larvae and pupae: These organisms possess breathing trumpets for gaseous exchange

Crabs: They can burrow fast into the mud against predators, strong waves or tides

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

Worms: They have strong protective and impermeable covering against high salinity

Mud skippers: These animals have fins adapted for crawling when on land and for swimming when in water

Fishes: Fishes like Tilapia have fins for movement and swim bladder for buoyancy

Factors Affecting Estuarine Habitats

The factors which affect estuarine habitats are common to aquatic habitats; these include:

• Temperature
• Wind
• Relative humidity
• Light
• pH, etc.