Understanding aqua ecosystems around us
Deep water lakes contain three distinct zones namely — Littoral zone, Limnetic zone and Profundal zone. Littoral zone: It is the shallow part of the lake closer to the shore, light penetrates up to the bottom and it ‘euphotic’ (having good light). This has rich vegetation and higher rate of photosynthesis, hence rich in oxygen. […]
Deep water lakes contain three distinct zones namely — Littoral zone, Limnetic zone and Profundal zone.
Littoral zone: It is the shallow part of the lake closer to the shore, light penetrates up to the bottom and it ‘euphotic’ (having good light). This has rich vegetation and higher rate of photosynthesis, hence rich in oxygen.
Limnetic zone: It is the open water zone away from the shore and it extends up to the effective light penetration level, vertically. The imaginary line that separates the L zone from the Profundal zone is known as zone of compensation/ compensation point/ light compensation level.
It is the zone of effective light penetration and here the rate of photosynthesis is equal to rate of respiration. Limnetic zone has no contact with the bottom of the lake.
Profundal Zone: It is the deep water area present below the Limnetic zone and beyond the depth of effective light penetration. Light is absent here and so are photosynthetic organisms thus the water is poor in oxygen content. It includes mostly the anaerobic organisms which feed on detritus.
The organisms living in Lentic habitat are classified into pedonic forms, which live at the bottom of the lake and those living in the open waters of lakes, away from the shore vegetation are known as Limnetic forms.
Biota of the Littoral zone:
Littoral zone is rich with pedonic flora (especially up to the depth of the effective light penetration). At the shore, proper emergent vegetation is abundant with firmly fixed roots in the bottom of the lake, and shoots and leaves are exposed above the level of water these are amphibian plants.
Certain emergent rooted plants of Littoral zone are the Cattails (Typha), Burlushes (Scirpus) and Arrowheads (Sagittaria). Slightly deeper are the rooted plants with floating leaves, such as the water lies (Nymphaea, Nelumbo, Trapa, etc.). Still deeper are the submerged plants such as Hydrilla, Chara, Potomogeton, etc. The free floating vegetation includes Pistia, Wolfia, Lemna (Duckweed), Azolla, Eichhornia, etc.
The phytoplankton of the Littoral zone are composed of Diatoms (Coscinodisus, Nitzschia, etc), Greenalgae (Volvox, Spirogyra), Euglenoids (Euglena, Phacus) and Dinoflagellates (Gymno dinium, Cysto dinium).
Animals, the consumers of the Littoral zone, are abundant in this zone of the lake. These are categorised into Zooplankton, Neuston, Nekton, Periphyton and Benthos. The zooplankton of the Littoral zone consists of water fleas such as Daphnia, Rotifers and Ostra cods.
The animals living at the air water interface constitute the Neuston and they are of two types – Epineuston and Hyponeston.
Water striders (Gerris), beetles, water bugs (Dineutes) form the Epineuston/ Super neuston and the Hypo neuston/ Infraneuston includes the larvae of mosquitoes. Animals such as fishes, amphibians, water snakes, terrapins, and insects like water scorpion (Rantral), back swimmer (Notonecta), diving beetles (Dytiscus), which are capable of swimming, constitute the nekton.
The animals that are attached to creeping on the aquatic plants, such as the water snails, nymphs of insects, bryozoans, turbellarians, hydras, etc., constitute the periphyton.
The animals that rest on move on the bottom of the lake constitute the benthos. Example: Red annelids, chironomid larvae, cryfishes, some isopods, amphipods, clam, etc.
To be continued…
– Dr Modala Mallesh
Subject Expert
Palem, Nakrekal, Nalgonda
Ph. 9989535675
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