Benthic Zone Definition | Benthic Zone Animals & Plants Ecosystem

Benthic zone

What is Benthic Zone?

The Benthic zone is the lowest zone and is the part of the ocean that is virtually absent of sunlight, which makes it difficult for plants to grow there. This zone is made up of a thin layer and consists of sediments and organisms that live on the bottom of a water body. It contains two subsections. The epipelagic or upper benthic zone is closest to the surface and sunlight, while the bathypelagic or lower benthic zone is furthest away from sunlight.

The epipelagic zone is the layer above the water’s surface, also called the photic zone, and the bathypelagic zone is below the epipelagic zone. The upper benthic layer contains organisms that can be found in this environment.

The lower benthic layer is much different than the upper benthic layer. It contains organisms sensitive to UVB radiation (the blue end of the spectrum) and is a much deeper environment than other ocean areas. It is a layer from 150 m to 10,000 m deep.

This layer is also home to organisms that live in oxygen-free environments. The term “deep sea” refers to this ocean layer and not how far from the surface it is.

The upper benthic zone contains organisms that are found in this environment. These organisms are the same density as the water and use it to their advantage. They can move around freely in this layer. The organisms in this layer have strong muscles, colorful skin, and hard skeletons.

Benthic Zone Animals

Benthic zone animals live on or under the surface of the seabed. Benthos is the collective name for all the organisms that live in, on, or under the sea bed (benthic zone), including organisms from both marine and freshwater environments.

Some pelagic species like whales and footprints and some microscopic larvae are benthic when they live at the sea bed but are pelagic when they swim in open water or fill their development stages or reproduction.

The benthic zone is where organic and inorganic nutrients from the surface layers of the ocean are deposited, and when food is abundant in the benthic zone, less food is available to species living in higher zones.  Animals that live in this area have to feed on detritus and other decaying plant and animal matter to survive.

Benthic zone characteristics include the presence of organic matter in the form of remains of previous animal meals and tissues and detritus and clays that accumulate in this way.

Benthic Zone Temperature & Salinity

Benthic zone temperature may vary from  0  to 10°C.   The weather and the season are two factors that can have an impact on the benthic zone temperature of any body of water.

Temperature is one of the most important parameters in determining the type of invertebrate life that can thrive. The temperature of the benthic zone alone dictates if we will find most of the invertebrates that live near the seafloor. The warmer the benthic zone is, the more invertebrates that will thrive there.

Benthic Zone Pressure

Benthic zone pressure varies from 0.3 to 1.0 MPa, and the density is about 1.7 to 2 g/cubic cm.

The benthic zone is characterized by several animal species, including protists, crustaceans, fish, and cephalopods (e.g., squid, octopus, cuttlefish).

Various other organisms live in this zone as well: plankton such as oikopleura spp.

Benthic Zone Plants

Benthic zone plants include bryophytes, conifers, gymnosperms, gymnosperms, and angiosperms.

When these plants were first discovered, conditions such as the type of substrate offered (i.e., surface level or substrate depth) were not controlled or well established; therefore, there was a lack of adequate information on the species composition that made up the benthic zone.

Benthic Zone Adaptations

The benthic zone is adapted to living on the ocean floor and to tolerating high pressures, low temperatures, and lack of light (photic zone)

Musculature

The benthos has muscular hydrostats with long bodies that are very flattened. Hydrostats have no air bladders for buoyancy or gas exchange. They are adapted to function at great depths in the ocean. They are slow swimmers. They have a small conical head, which is bifurcated at the tip.

This makes them look like a spade with eyes and antennae on top, hence their name spadix and pseudopus (spade-foot)

Exoskeletons

The pseudopod has an exoskeleton. This means that the benthos is encased in hard skeletal plates that are attached by flexible muscles, tendons, joints, and ligaments. The exoskeleton is not just a rigid shell to protect the benthic zone.

It functions as a complex jointed frame with 60 times the number of muscle cells in the animal’s body. As an animal grows, muscles and tendons are damaged, and this limits growth. The exoskeleton is, therefore, an important component of benthic fitness (Darwin).

Habitat and distribution

Benthic zone animals live on or in the soft sediments of the deep-sea floor. This is an extremely inhospitable environment, and they are adapted to tolerate pressure, temperature, lack of light, and nutrient deficiency.

These animals have flattened bodies to minimize their profile in the sediment. Many have exoskeletons that function as a jointed frame that resists bending forces (unlike most fish with bone, which bends easily).

The benthic zone includes a diverse range of animals from plankton to large fish and invertebrates, including some of the most famous animals of all: the flatworms.

Importance of Benthic Zone

The benthic zone has many uses.  It is used for many reasons, including research and fishing. This is a major part of how humans make money by selling fish and seafood products that they catch from the ocean. Though this can be extremely dangerous, as fishing on the ocean floor is extremely hard.

It is also known as the deep sea, and it is home to many different organisms, such as fish and shellfish. These organisms are found in the deep sea, which is mainly only accessible by commercial companies that own high-tech equipment.

The benthic zone also contains algae and other bacteria that are used for different types of research.