The Benthic Zone

Benthic Zone

• refers to the ecological zone located at the bottom of any marine or freshwater body, such as a river, ocean, lake or pond.

• this includes the sediment surface

• found all across the world, wherever there is an appreciable water body.

• low temperature

• high pressure

• minimal sunlight

Benthic zone may be characterized by:

Sediment layers

This layer in the benthic zone help in the recycling of nutrients, which in turn makes it possible for the sustenance of rich aquatic life in the upper water column.

warmer; 2°C to 3°C

The temperature is — in benthic zones located close to the shore or with notably shallow depth, but for those located hundreds of meters deep, temperatures can fall to — (near the abyssal zone). Aquatic life that can survive in such extreme cold temperatures is limited, and those found there often move at a slow pace to conserve energy.

Low; high

— pressure lies in shallow benthic zones, and — pressure for those located a few thousand meters deep.

Mariana Trench

The —, which happens to be the deepest trench on Earth (around 10,000 meters below sea level), is the extreme example for a very high-pressure benthic zone.

• The pressure here is roughly 1000 times the normal pressure in sea level.

homogenous; higher

High-pressure benthic zones lead to a very — environment, which produces organisms with distinctive traits. One peculiar example is the enlarged sizing of certain marine creatures. Also, at great oceanic depth, the quantity of dissolved oxygen in the water is —, which makes organisms grow larger than their counterparts in more temperate zones.

decreases

The intensity of light — with depth. It becomes limited at depths below 250 meters.

dysphotic; zero

Between 250 and 1000 meters, the intensity of light begins to dissipate very quickly. This zone is called the — zone and performing photosynthesis here is very difficult. Beyond a depth of 1000 meters, light availability is almost —, with photosynthesis no longer feasible.

scarce; adapt

Nutrient availability in the deep sea is also —, so organisms need to — themselves accordingly to survive here.

benthos

• Organisms living in the benthic zone are called —.

• they have specially adapted themselves to live on the bottom substrate in deep water bodies with elevated pressure and cold temperatures.

• In fact, organisms that inhabit the deep-water pressure areas cannot survive in the upper parts of the water column.

detritivores

Most of these benthos are —.

dead organic matter

Due to the scarcity of light, the source of energy for benthos is often in —from the organisms higher up in the water column that settle on the benthic belt after death. This dead organic matter provides nutrition to benthos and completes the aquatic food chain and nutrient recycling.

1. Epifauna

2. Infauna

Categories of benthos (2)

Epifauna

A type of benthos living on or near the surface of the ocean floor

Infauna

A type of benthos that live burrowed under the sea floor

water column; sediment layers

Benthos play an important role in regulating the nutrient flow between the — and —.

buffer

Benthos, which mostly consist of detritivores subsisting on dead and decaying matter, help in decelerating the flow of nutrients by storing the nutrients in their body for long periods of time. This acts as a — that is useful in preventing an excessive influx of elements.

• Example: micro algae buffer nutrients that prevent phytoplankton overexploitation, which would otherwise lead to eutrophication.

slime

In shallow benthic zones that receive manageable amounts of sunlight, micro algae are ubiquitous. They can photosynthesize by taking up CO₂ and a handful of micronutrients. Most of the carbon consumed by them is later released as extracellular polymeric substances, commonly called —.

Extracellular Polymeric Substances (EPS)

— is sticky organic matter comprised of biofilms and facilitates the attachment of cellular substances to the sediment surface. The stickiness of — holds sediment particles together so they can avoid resuspension, which helps in stabilizing the dissolved oxygen levels.