Aquatic Habitats

Habitat is a place where organisms (plants, microorganisms and animals) are naturally found e. g. the habitat of tadpole is the bottom of fresh water 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 habitats

Marine habitats refer to aquatic habitats which contain salt water. E.g are the oceans, shores and the open seas.

Characteristics of marine habitat

  1. Salinity: It has a high salinity and its average salinity is put at 35 parts per 1000 or 3.5%.
  2. Size: Marine habitats represent the largest of all the habitats. The ocean occupies over 70% of the earth's total area.
  3. Light penetration: Light penetrates the ocean water only to a maximum depth of 200 meters. Penetration depends on the turbidity.
  4. Oxygen concentration: The oxygen concentration is highest at the surface while the very deep part of the oceans has no oxygen.
  5. Chemical composition :- marine water consists of many kinds of dissolved ions including Na+, K+, Mg2+, Ca2+, Pb43-, I-, NO3- e.t.c.
  6. 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 increase in the depth of the sea.
  8. 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.

Major zones of the marine habitat

The major ecological zones of the marine habitat include:

  1. Supratidal or splash zone: This is the exposed zone of the marine habitat.
  2. Intertidal or neritic zone: This zone which is also called planktonic zone is only exposed at low tide or covered by water at high tide. This zone has high photosynthetic activities because of abundant sun shine. Water temperature fluctuates.
  3. Litoral or subtidal zone: This zone is about 200m deep, it is constantly underwater, it has abundant sunlight and nutrients.
  4. Benthic zone: It is about 500m deep, it has low light penetration and low nutrients
  5. Pelagic or abyssal zone: It is about 700m deep, low temperature, low light penetration, high pressure and low photosynthetic activities
  6. Hadal or aphotic zone: It is the deepest, over 7000m deep. This forms the floor or the bed of the ocean. No light penetration or photosynthesis

On the basis of depth and light penetration, there exist three major zones:

  1. Euphotic zone: a zone directly connected with sunshine, photosynthesis take place
  2. Disphoticzone: a region of dim light, consumers and decomposer are found here, light intensity is too low for photosynthesis.
  3. Aphotic zone: this represents the bottom or bed of the seas with cold dark ater without light penetration.

Adaptive features found in organisms in marine habitat

Plants found in marine habitats have various adaptive features:

  1. Sea weeds: They possess hold-fasts for attachments. They also possess mucilaginous cover to prevent dissociation. They have divided leaves, floating devices or air bladder for buoyancy
  2. Phytoplanktons: An example is diatoms. They possess air spaces in their tissues, rhizoids (fake feet) for attachment to rocks and air bladder for buoyancy.
  3. Algae: An example is Sargassum. Algae possess chlorophyll for photosynthetic activities, small size or large surface area for drifting or floating.

Marine animal possess a variety of traits to help them survive in their environment:

  1. Cartilaginous fishes like shark and dogfish have the ability to retain urea in their body to cope with high salinity.
  2. Crabs: They are capable of burrowing fast into the mud to protect them against predators, strong waves or tides.
  3. Bony fish: Fish 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.

Estuarine Habitat

The estuarine habitat is a region from where rivers empty their water into ocean, it is formed at the coastal line. The mixing of the ocean with fresh water as a result of the action of the tides leads to formation of brackish water. The brackish water is called estuary(estuarine).

Characteristics of Estuarine habitats

  1. Varying salinity: The salinity of estuaries fluctuates. It increases when the tide rises and sea water flows into the fresh water and decreases when the tide becomes low and water flows out from the estuary to the sea
  2. Low oxygen concentration: Oxygen content in estuarine habitat is generally very low and as a result much of microbiological activities are anaerobic.
  3. Population of species: The estuarine habitat has low number of species compared to the marine habitat.
  4. Shallowness: In estuaries, water is shallow as compare to the sea.

Examples of estuarine

  1. Delta: Delta is where a river divides into many channels before entry into the ocean or sea. Estuary(delta) is formed at the mouth of a river as it enters the sea.
  2. Lagoon: A lagoon is a shallow body of ocean that enters into the land in the form of canal and mixes with the fresh water of rivers and streams.
  3. Bay: Bay is a small but similar form of lagoon in which ocean water enters into the land and mixes with fresh water from the 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 a bay is very small and not long enough to rejoin the sea in another end.

Adaptive features found in organisms in estuarine habitat

Plants found in estuaries include planktons, algae, red and white mangrove and they have the following adaptive features:

  1. White mangrove: Due to the low oxygen content they develop breathing roots called pnematophores, from the water-logged soil. These root project upwards for absorbing the atmospheric oxygen.
  2. Red and white mangroves: They develops stilt roots. The rootlets of such root help in absorbing the nutrients from the mud
  3. Paspalum: The leaves of this plant have thick layer of cuticle to check the rate of respiration

Animals including mosquitoes, crustaceans, mollusca, worms, fishes e.t.c. found in estuaries survive possessing the following features;

  1. Crustaceans and water snails burrow into the mud against predators, strong waves or tides.
  2. Mudskippers have fins for crawling on land and swimming in water.
  3. Fishes have fins for movement and swimming bladder for buoyancy.
  4. Mosquito larvae and pupae possess breathing trumpets for gaseous exchange

Freshwater Habitat

This is a body of water formed mainly from inland waters and it contain very low or no salt. y. Examples are rivers, ponds, streams, springs and lakes. Fresh water is of two types based on its mobility:

Characteristics of fresh water habitats

  1. Salt concentration: It contains little or no salt. Salinity is 5 parts per thousand i.e. 0.5%
  2. Oxygen concentration: Oxygen concentration is high, being available in all parts of the water body, especially at the surface.
  3. Temperature variation: The temperature of freshwater habitat usually varies with season and depth
  4. Shallowness: The water is shallow, hence sunlight penetrate to the bottom.
  5. Seasonal Variation: Fresh water habitats like streams and rivers dry up during the dry season while others reduce in volume. Speed of flow is usually high during the rainy season than in dry season.

Zones of freshwater habitat

For Lentic fresh water habitats, there are two zones. These are littoral and benthic zones.

  1. Littoral Zone: It is shallow and contains several plants and animals. It has the highest level of primary production because sunlight can easily penetrate the zone. Plants associated with this zone include Spirogyra, Chlamydomonas, water lettuce, duck weed, e.t.c. animals associated with this zone include water snails, flatworms, tadpoles, crocodiles and Hippopotamus.
  2. Benthic zone: It is the deepest zone and does not have rooted vegetation. Plants associated with this zone include water lily, fern and grasses. These have well developed root system in the mud. Animal found here include protozoa, Tilapia fish, mud fish, catfish, water scorpion, crayfish, e.t.c.

There are two zones in a lotic fresh water habitat. These are pool zone and rapid zone.

  1. Pool Zone: in this zone, water is relatively slow and calm
  2. Rapid zone: in this zone, water is fast. The lotic fresh water habitat is not as stratified as the lentic fresh water habitat.

Adaptive features found in organisms in freshwater habitat

Plants found in freshwater habitats have the following adaptive features:

  1. Water lily: The plant has air bladder, expanded shape and light weight which keeps it afloat. It has long petioles attached at the center of leaf blade which prevent them from being drawn under water by the current.
  2. SpirogyraThe plant has mucilaginous cover which protects them in water
  3. Hornwort: The plants have submerged or thin dissected leaves which increases their surface area to sunlight and gaseous exchange.

Animals found in freshwater habitats have the following adaptive features

  1. Hydra has slippery surface, hooks and suckers for attachment to water particles.
  2. Duck has webbed feet for locomotion and serrated beak for sieving food in water into its mouth.
  3. Fishes have swim bladders for buoyancy and gills for respiration
  4. Pondskatters has long legs for skating on water surface
  5. Water boatman can carry bubbles of air with it as it goes below the water surface to the bottom and uses these as their air supply under water
  6. Protozoa have contractile vacuole for osmoregulation in water.