Aquatic And Estuarine Habibat SS1 Biology Lesson Note

HABITAT (AQUATIC HABITAT)

A habitat is a place where organisms (plants, microorganisms and animals) are naturally found e. g. the habitat of a tadpole is the bottom of freshwater ponds or streams.

There are three main types of habitats, namely; aquatic habitat (in or around water), terrestrial habitat (in or on land) and arboreal habitat (in or on trees).

There are three kinds of aquatic habitat;

marine/saltwater habitat e.g. ocean, seas

brackish water habitat (where salt and fresh water mix) e.g. delta, lagoon, bay

Freshwater habitat (contain little or no salt) e.g. lakes, rivers, streams.

 MARINE HABITATS

Characteristics of marine habitats are as follows:

1. The marine habitats constitute the largest habitat in the biosphere (70% of the earth’s area)
2. They do not undergo sudden or rapid changes in physical factors such as temperature, PH and specific gravity. Hence they show the greatest stability of all habitats.
3. Chemical composition :- marine water consists of many kinds of dissolved ions including Na+, K+, Mg2+, Ca2+, Pb43-, I-, NO3- e. t. c.
4. Hydrogen (H+) concentration (PH): – salt water is alkaline in nature with PH of about 8.0 – 9.0 near the surface.
5. Salinity (salt concentration of water). The seawater has a high salinity. The average salinity of seawater is 35 parts per thousand.
6. The density of marine water is high. It is about 1.028 while that of fresh water is 1.0. This allows many organisms to float in it.
7. The temperature of the sea changes less quickly than that of the land. However, the temperature falls with an increase in the depth of the sea.
8. Oxygen concentration is highest at the surface where the atmospheric oxygen is dissolved in water. The concentration of oxygen decreases with depth.
9. Waves are temporary movements of surface water of the sea which occur in any direction. They are caused by wind blowing against the surface of water. They also bring about the mixing of seawater. 

Waves can also beat against the shore and sometimes cause it to be eroded.

10. Tides are alternate rise and fall of the surface of the sea at least twice daily. Tides are caused by water distribution resulting from the combined gravitational pull of the earth by the sun and moon.

ZONATION OF MARINE HABITAT

1. HORIZONTAL ZONATION

The marine habitat is made up of the seashore and open sea. The major zones of the marine habitat are generally as follows

The supratidal or splash zone is the exposed zone with occasional moisture being the area where water splashes when waves break at the shore.

i. Intertidal or neritic zone is the planktonic zone which is exposed at low tide or covered by water at high tide. This zone has high photosynthetic activities because of abundant sunshine. Water temperature fluctuates.

ii. The subtidal or littoral zone is about 200m deep, constantly underwater, with abundant sunlight and nutrients.

The benthic zone is about 500m deep with low light penetration and low nutrients. The water is dark, cold and with little oxygen. Hence, it is unfavourable for life.

iii. The abyssal or pelagic zone is about 7000m deep with low light penetration, low temperature and high pressure. The low light leads to low photosynthetic activities. Hence food production is primarily by chemosynthesis.

iv. Hadal or aphotic zone is the deepest, over 7000m deep. This forms the floor or the bed of the ocean. No light penetration or photosynthesis

2. VERTICAL ZONATION 

Based on light penetration or depth, the marine habitat can be zoned into three ;

i. Euphotic zone is the area in direct contact with sunshine. Hence, there is enough light penetration for photosynthesis. Therefore producers, consumers and decomposers are all present.

ii. Disphotic zone is a region of dim light. Light penetrates the water with low too intensity for photosynthesis to take place. Consumers and decomposers are found in this zone.

iii. The aphotic zone is the bottom or bed of the seas and oceans. It is characterized by cold dark water without light penetration and very few living organisms.

DISTRIBUTION OF ORGANISMS AND ADAPTATION TO MARINE HABITAT

Organisms of the splash zone include periwinkles; crustaceans e.g. ghost crabs, seaweeds and sargassum (algae). 

Those in the intertidal zone include starfish, sea anemones, sponges, sea urchins, annelids, mollusca and barnacles.

i. In the subtidal zone are snails, crabs, lobsters and crayfish.

ii. The benthic zone is unfavourable for life. The producers are absent, and only a few saprophytic animals are present.

iii. The neritic zone houses plankton (microscopic floating organisms e.g. diatom, algae, protozoa, crustaceans and worms) and nekton (e.g. fishes, crabs, prawns and whales).

iv. Oceanic water houses sharks, croakers, sea catfish, mackerel, bonga fish etc.

 ADAPTATION OF ANIMALS TO MARINE HABITAT   

Animals including barnacles, fishes, crustaceans etc. found surviving in marine habitats do so with the following adaptive features

1. Barnacles have:

• Protection mantle for attachment to rock shore and water retention 
• Cilia for feeding. 
•  Shell that prevents desiccation (drying up)

2. Fishes possess 

• reduced or no kidney to retain urea in their body to cope with high salinity e.g. cartilaginous fishes like shark, dogfish etc. 
• Salt-secreting glands in their gills or eyes for maintaining osmoregulation (salt balance) e.g. bony fishes like tilapia, herring etc. 
• Tube feet which enable them to hold on to rock shores and hard shells to prevent desiccation e.g. starfish, whales.

3. Whale has 

• fins for stability in water 
• An organ in front of the nostril for detecting pressure changes in water. 
• iii. A thick layer of dermal fat insulation or food reservoir.

4. Shrimps possess powerful claws for holding food or prey.

5. Periwinkles possess lungs for breathing and feet for attachment.

6. Crabs burrow fast into the mud to protect them against predators, strong waves or hide.

ADAPTATION OF PLANTS TO MARINE HABITAT

Plants such as seaweeds, algae, Vesuvius and diatoms are naturally found in marine habitats with the following adaptive features;

1. Seaweeds have 

hold–fast for attachment. 

1. mucilaginous cover to prevent desiccation. 

iii. Divided leaves or floating devices for buoyancy.

2. Algae (e.g. sargassum) have 
3. chlorophyll for photosynthesis. 
4. Small size or large surface area for floating in water. 

3. Planktons (e.g. diatoms) possess; 
4. air space in their tissues 
5. Rhizoid for attachment to rocks 

iii. Air bladder for buoyancy (floating).

Examples of food chains in a marine habitat include:

1. Diatom → crabs → tilapia
2. Diatom →zooplankton → tilapia →shark

ESTUARINE HABITATS (BRACKISH WATER HABITATS)

An estuary is a body of water formed at the coast where freshwater flowing towards the sea mixes with the sea (salt water) flowing inland. Estuarine habitats include deltas, lagoons and bays.

CHARACTERISTICS OF ESTUARIES

1. The salinity fluctuates.

2. The specific gravity is less than that of the sea.

3. They have high turbidity due to frequent disturbances. Hence the rate of photosynthesis and respiration by organisms reduces.

4. The water is shallow.

5. They have a low diversity of species compared to marine habitats.

6. They have high levels of nutrients

7. They have low oxygen content, hence anaerobic activities are common.

PLANTS DISTRIBUTION AND ADAPTATION IN ESTUARIES

Plants found in estuaries include plankton, algae, and red and white mangroves and they have the following adaptive features; 

1. Planktons (diatoms) have; 
2. air spaces in their tissues 
3. Rhizoid for the attachment to rock shores 

iii. Air bladder for buoyancy

2. Algae have: 
3. chlorophyll for photosynthesis 
4. small size or large surface area for floating in water

3. Red mangrove has; 
4. Stilt roots with rootlets that have air spaces for air conduction to the root tissues and support to prevent washing away of the plant by the tide 
5. Seeds which germinate while they are still on the parent plant, thus preventing the carrying away of the seedlings by water current.

4. White mangrove has pneumatophores (breathing roots) for gaseous exchange.

ANIMAL DISTRIBUTION AND ADAPTATION

Animals including mosquitoes, crustaceans, molluscs, worms, fishes etc. found in estuaries survive by possessing the following features;

1. Mosquito larvae and pupae possess breathing trumpets for gaseous exchange

2. Crustaceans and water snails burrow into the mud against predators, strong waves or tides.

3. Worms have strong protective and impermeable covering against high salinity.

4. Mudskippers have fins for crawling on land and swimming in water.

5. Fishes have fins for movement and swimming bladders for buoyancy.

FOOD CHAIN IN ESTUARINE HABITATS

Detritus → worms → snails → birds

Diatoms → shrimps →fishes 

Diatoms → small fish → sharks → man 

ASSIGNMENT

1. Buoyancy in salt water is ensured by the following except 
2. divided leaves B. chlorophyll C. floating devices D. air bladder

2. The mucilaginous cover in seaweed and spirogyra is mainly for  
3. protection B. osmoregulation C. avoiding desiccation D. feeding

3. Which of the following is not a freshwater habitat? 
4. puddle B. swamp C. stream      D. sea

4. Which of these is not an adaptive feature in a marine habitat? 
5. bladder for floating     B. hold fast for attachment C. fur to prevent water loss                           D. rhizoid for attachment to rock

5. The following are characteristics of freshwater habitats except 
6. low salt content      B. high salinity C. shallow water D. can be stagnant or running water

6. In a tabular form, state five differences between fresh water and a marine habitat

7. State three adaptive features of each of the plants and animals in the freshwater habitat