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Benthic zone is the zone located at the bottom of a marine or freshwater body.”

“Benthic zone is the zone located at the bottom of a marine or freshwater body.”

The benthic zone begins at the shore and extends to the bottom of a waterbody. It is found all over the world. Only a small amount of sunlight reaches this zone. This zone is characterized by low temperature and high pressure. Such conditions are not optimum for sustaining vast flora and fauna found in this zone. The sediment layers of the benthic zone help in recycling the nutrients that helps in the survival of the aquatic life in the upper column.

Following are the important characteristics of benthic zone:

The benthic zones located close to the shore are warmer than those located hundreds of metres deep. Very limited organisms can survive at such lower depths and the ones that do, move at a very slow rate.

The pressure varies from low to high depending upon the depth of the benthic zone. The pressure is lower at shallow depths when compared to hundreds of metres deep. The Mariana Trench is an example of very high pressure benthic zone with a pressure 1000 times more than the normal pressure.

At such high pressure zones, the organisms found have very large size. Also the dissolved oxygen at such great depths is higher that results in enlargement of the organisms.

As the depth increases, so does the intensity of light. The intensity of light begins to dissipate quickly between 250 to 1000 metres and this zone is known as the dysphotic zone. Due to the low availability of light, it is very difficult to perform photosynthesis here. Beyond 1000 metres, there is no availability of light and hence no photosynthesis can occur.

The organisms found in the benthic zone are known as benthos. Since the nutrient availability is scarce in the deep benthic zones, the organisms found here have adapted themselves to survive here. They are also acclimatized to high pressures and cold temperatures.

Most of the organisms found in this zone constitute detritivores. Dead organic matter is the main source of energy for benthos. This provides nutrition to the detritivores found here and completes the aquatic food chain and nutrient recycling.

Benthos that are found on the ocean floor are known as epifauna, while those found at greater depths are known as infauna.

The organisms present in the benthic zone regulate the nutrient flow between the sediments layer and the water column. The detritivores that feed on dead and decaying matter store the nutrients in their body for a longer period of time and thus help in decreasing the flow of nutrients.

Microalgae are found in the shallow benthic zones where sunlight is adequate. They undergo photosynthesis by utilising carbon dioxide and micronutrients. The consumed carbon is released as extra polymeric substance known as slime.

The sticky slime holds the sediment particles together, that stabilizes dissolved oxygen levels. The slime is also metabolized by the bacteria present on the ocean bed because it acts as a source of nutrients for bacteria. Thus the extra polymeric substance plays a key role in maintaining the local food web and the sediment structure of marine ecosystem.

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