Aquatic Ecosystem Zones and Habitats - Class IX

The photic zone or euphotic zone is the depth of the water in a lake or ocean, that is exposed to such intensity of light at which the rate of oxygen consumption, is equal to the rate of carbon dioxide production. It extends from the surface down to a depth where light intensity falls to one percent of that at the surface, called the euphotic depth. About 90% of all marine life lives in the euphotic zone.

Benthos are the organisms found at the bottom of freshwater bodies such as lakes, rivers, and streams and since light cannot reach such deep water, therefore, they depend upon organic matter. This dead and decaying matter sustain their food chain hence, they are mostly scavengers or detritivores, belonging to primary consumers of detritus food chain.

Benthos are organisms that live on or in the bottom sediments of a body of water, such as lakes or oceans.

The abyssal zone is the deep ocean layer where sunlight does not penetrate, meaning photosynthesis cannot occur. It relies on organic matter falling from above to support consumers and decomposers.

The profundal zone is the deep, aphotic (lightless) region of a lake, located below the limnetic zone and above the benthic zone.

Benthic animals are those that live on or in the bottom substrate of aquatic environments, such as the deep sea or lake beds.

Ponds and lakes are stationary fresh water ecosystems. Ponds are generally shallower with depth less than 2 meters. Shallow lakes are eutrophic with rich biota and quick circulation of nutrients. Producers in a pond or lake ecosystem include phytoplanktons like diatoms, desmids, Chlorella, Chlamydomonas, Spirogyra, Chlamydomonas, Oedogonium etc. Littoral zones occur on the edge of large lakes and rivers, having dense growth of vegetation. Therefore, the correct answer is option B.

1. The zone at the edge of a lake or sea or in an aquatic habitat which is alternatively exposed to
   air is called 'Littoral zone'.
   2) Therefore, sunlight is also available here which penetrates to the sediment level and immersed in water, which helps and allow to grow aquatic plants.
   3) This coastal zone is rich producers from the surface to bottom, with a large number green alga
   4) Organisms which are mobile such as crabs, snails, limpets are usually found in these areas.
   So, the correct answer is 'Sea'

Aquatic light penetration creates three distinct zones. The euphotic zone receives sufficient light for photosynthesis. The disphotic zone receives some light but insufficient for photosynthesis. The aphotic zone receives no sunlight at all. This order from surface to depth is fundamental to aquatic ecosystem structure.

In stratified lakes, the metalimnion is the middle transitional layer characterized by a steep temperature gradient, also known as the thermocline. It separates the warmer upper epilimnion from the colder lower hypolimnion.

Littoral zone is the shallow coastal zone. Light is available upto bottom in this zone. Therefore, producers are found throughout from surface to bottom in this zone. Rooted vegetation occurs along shores. Consumers are also available throughout, i.e., from surface to the bottom in this zone.

The abyssal zone is the abyssopelagic layer or pelagic zone, that contains the very deep benthic communities near the bottom of oceans. The benthic zone begins from shore to continental shelf. The deep sea floor is called as the abyssal plain.

Benthos is the community of organisms that live in or near the seabed. This zone is called as the benthic zone. Chronomid larvae, phantom larva, clams, red annelids are some organisms that belongs to benthose of a lake.