AQUATIC HABITAT

AQUATIC HABITAT

An aquatic habitat is a natural body of water in which certain organisms live naturally. There are three types of aquatic habitats:

1. Marine habitat (salt water habitat)
2. Estuarine habitat (brackish water habitat)
3. Fresh water habitat

MARINE HABITAT

Marine habitat is an aquatic habitat that contain salt water e.g. oceans, seas, lakes, sea shores.

Characteristics of marine habitat

1. Salinity: salinity of marine habitats is high, at about 35.2 parts of salt per thousand (35‰)
2. Size: size of marine habitats is very large
3. Density: density of marine water is high at about 1.028g/cm³; this causes organisms to float in it.
4. Pressure: the water pressure of marine habitat increases with depth at one atmosphere for every 10m. The pressure at the bottom is high.
5. Temperature: the temperature of marine habitats decreases with increase in depth. The temperature is about 30̊C at the top and 4̊C at the ocean floor.
6. Oxygen concentration: the oxygen content of marine water is highest at the top where atmospheric oxygen dissolves in the water and decreases with depth.
7. Hydrogen ion concentration (pH): marine water is alkaline with a pH of 8.0 - 9.0.
8. Light penetration: light penetrates the marine habitat to a depth of about 200m. This is due to water turbidity.
9. Marine habitats are usually affected by waves, ocean currents and tides.

Major Ecological Zones of Marine Habitat

1. Supratidal zone (splash zone): this is the exposed zone of the marine habitat; it is land where water splashes when waves break at the sea shore.
2. Intertidal zone (neritic zone): this zone is exposed at low tide and submerged at high tide.
3. Subtidal zone: is about 200m deep and constantly submerged by water.
4. Bathyal zone: this zone is about 3000m deep and is characterized by low light penetration
5. Abyssal zone: this zone is ab0ut 7000m deep. It is characterized by low temperature, low light penetration and high pressure
6. Hadal zone: this zone is up to about 10000m deep. It is characterized by no light penetration, very low temperature, high pressure and no photosynthetic activity.

On the basis of light penetration, marine habitat can be categorized into:

• i. Euphotic zone: has enough light penetration. Photosynthetic activities are high. Producers, consumers and decomposers are present here.
• ii. Disphotic zone: has dim light. Only consumers and decomposers are present.
• iii. Aphotic zone is the dark ocean bottom with no light penetration. Very few organisms are present here.

Distribution of organisms in marine habitat

Plants in the splash zone include grasses and Ipomea. Animals found here are sand crab and ghost crab.

Organisms in the intertidal zone include starfish, bivalve mollusc, mole crab, Limpet, barnacles, crabs, sea anemones, sea urchins, crabs and worms. Plants found here include Sargassum, sea lettuce and brown algae.

Organisms in the subtidal zone include starfish, polychaete worms, brown algae, red algae, prawn, shrimp, phytoplankton, zooplankton, squid, cartilaginous fish and bony fishes.

Other organisms of the deep ocean are shark, ray, sea catfish, croaker and angler fish.

Adaptive features of Organisms in Marine habitat

1. Star fish, bivalve mollusc, mole crab, sand crab and ghost-crab burrow into the soil to prevent being washed away by waves and to avoid desiccation during low tide.  They also possess gills for gaseous exchange in water and spongy tissue for gaseous exchange on land.
2. Star fish and bivalve mollusc have protective colouration like sand to prevent being detected by predators.
3. Limpets, barnacles, sea urchins and sea anemones attach themselves firmly to the rocks by the feet to prevent being washed away by waves
4. Barnacles have protective shell and enclose water in its shell to prevent desiccation.
5. Sea weeds possess hold fast for attachment and air bladder for buoyancy.
6. Algae, phytoplankton have small sizes to enable them float to reach light for photosynthesis.
7. Prawns and shrimps have gills for gaseous exchange, appendages for locomotion and exoskeleton to prevent water-loss from the body.
8. Bony and cartilaginous fish have gills for gaseous exchange, scales to prevent water-loss from the body and air bladder to adjust its depth within the water body.
9. Organisms of the benthic zone have fluorescent organs that produce light to attract their prey, have large mouths to capture their prey and can withstand high pressure and low oxygen concentration.

Food chain in marine habitat

Diatom → krill → squid → whale

Algae → limpet → whelk → seagull

ESTUARINE HABITAT

Estuarine habitat is a body of water where salt water from the sea mixes with fresh water from the land to produce brackish water. In Nigeria, estuaries are found in coastal zones of Lagos, Ondo, Edo, Delta, Akwa Ibom, Bayelsa, Rivers and Cross rivers.

Types of Estuaries

There are three types of estuaries

    a.  Bay: a little portion of sea water that enters into land to mix with fresh water.

    b.  Delta: where a river divides into many channels before entering the sea.

    c.  Lagoon: this is when sea/ocean water enters into land by means of a canal.

Characteristics of Estuarine Habitat

1. Fluctuations in salinity: the salinity of an estuary is lower at the mouth of the river and higher towards the sea
2. Turbidity: the turbidity of estuarine habitat increases especially during the rainy season due to the debris brought by flood water.
3. Shallowness of water: estuarine habitat is shallow due to deposition of debris by rivers. It is not as deep as marine habitat
4. High level of nutrients: estuarine habitat is characterized by high amount of nutrients
5. Low oxygen content: the oxygen content of an estuarine habitat is very low
6. Low species diversity: the species diversity of estuarine habitat is lower compared to that of marine habitat.

Distribution of Organisms in Estuarine Habitat

Plants in the estuary are phytoplankton, algae and epiphytic plants, Spartina, Salicornia, sedges, bulrush, saltgrass, Thalassia, red mangrove (Rhizophora racemosa), white mangrove (Avicennia nitida).
The animals are oysters, anemones, clams, crabs, lobster, shrimps and salmon fish

Adaptive Features of Organisms in Estuarine Habitats

1. Planktons / Diatoms possess air spaces in their tissues for buoyancy so as to reach light. They also have rhizoids/false feet for attachment to rocky shores
2. Algae possess chlorophyll for photosynthesis and air bladder for floating.
3. White mangrove possess breathing root (Pneumatophores) for exchange of gases.
4. Mosquito larva has breathing trumpets for gaseous exchange
5. Mudskipper fish have fins adapted for crawling when on land and swimming when in water
6. Worms have strong protective and impermeable covering against high salinity.
7. Crabs burrow fast into the mud to escape predators, strong waves or tides.

Food chain in Estuarine habitat

Detritus → shrimp → Salmon

Detritus → worms → snail → bird

FRESH WATER HABITAT

Fresh water habitat is an aquatic habitat that contain very low level of salinity e.g. rivers, springs, streams, lakes.

Characteristics of freshwater habitat

1. Low salinity: freshwater habitats contain no significant amount of salt
2. Small size: the body of freshwater habitats are small compared to marine habitats.
3. Variation in temperature: the temperature of freshwater habitat varies with depth and season. The temperature at the top is slightly higher at the top than at the bottom. The temperature during the hot season is also higher than the temperature during the cold season.
4. Shallow depth: freshwater habitats are usually shallow; this allows light penetrate through to the bottom.
5. High concentration of oxygen content: the concentration of oxygen in freshwater habitats is high and evenly distributed round the water body.
6. Seasonal variation: some rivers dry up during the dry season and increases in volume during the rainy season.
7. Currents: currents are present in freshwater which affects the distribution of gases and nutrients.

Types of freshwater habitats

There are two types of freshwater habitats on the basis of their mobility:

1.  Lentic freshwater: these are standing or stagnant water e.g. ponds, pools, lakes, swamps, dams
2.  Lotic freshwater: these are running waters which flow continuously in one direction e.g. rivers, streams, springs

Major Ecological Zones of Freshwater Habitats

Lentic freshwater habitat is divided into two zones:

a)  Littoral zone: this is the shallow part of the freshwater habitat. It contains several plants and animals.

b)  Benthic zone: this is the deepest part of the freshwater habitat. It does not have as much plants as littoral zone.

Lotic freshwater is also divided into two zones:

    a)  Pool zone: this is where the rate of water flow is slow and calm

    b)  Rapid zone: this is where the speed of water flow is very fast. 

Distribution of Organisms in a Freshwater Habitat

Some of the organisms found in the littoral zone of the freshwater habitat include Spirogyra, Chlamydomonas, water lettuce, water fern, duckweed, diatoms, reeds, sedges, water fleas, water snails, water skater, ducks, frogs, toads, tadpoles, hydra, snakes, crocodiles, waterbuck and hippopotamus.

Organisms found at the benthic region of freshwater habitat include water lily, ferns, commelina, hydra, Tilapia fish, mud fish, cat fish, leech, pupae of mosquito, crayfish, water snail, water scorpion, water boatman and water bug.

Adaptive features of organisms in freshwater habitat

1. Water hyacinth and water lily have air bladders, intercellular space and light weight that enable them float in the water. They also have broad leaves that helps in absorbing sunlight for photosynthesis.
2. Spirogyra has mucilaginous cover which protect them in water.
3. Water lettuce has hairs on their leaves which help them to trap air and enable them to float
4. Water boatman carries hair bubbles with it to the bottom of the pond for respiration under water
5. Water skater has long legs with which it skates on water surface
6. Lungfish carries out gaseous exchange with gills under water and when the river dries out, it burrows into the soil and begin to use lungs

Food Chain in Freshwater Habitat

Algae → Tadpole → Dragonfly larva → water stick insect