Divisions of Marine Environment
Pelagic Zone
The pelagic zone includes all ocean waters away from shores. The term pelagic is derived from
the Greek word pelagos, meaning "open sea." It is divided into five depth zones with varying
environmental conditions and sea life.
The neritic zone is the shallow part of the ocean located between the intertidal zone and the
oceanic zone. It has a maximum depth of about 200 meters (650 feet), allowing sunlight to reach
the entire seafloor over the continental shelf and making it part of the ocean's photic zone.
Factors that make the pelagic zone unique include:
1.It covers more than 50% of the Earth in water, more than 3.2 kilometers (2 miles) deep.
2.It makes up more than 99% of the inhabitable space on our planet.
3.The deepest part of the ocean, the Mariana Trench, is about 11,000 meters (7 miles) deep.
4.The open ocean produces more than 50% of the world's oxygen.
5.It is a critical carbon sink, storing 50 times more carbon dioxide than the atmosphere.
Many of its inhabitants never experience sunlight.
Layers of the Pelagic Zone or sub division of Pelagic zone.
The pelagic realm (Oceanic province) is divided into five distinct regions based on average depth
and sunlight availability. Moving from the surface to the ocean floor, the zones are labeled:
1.Epipelagic
2.Mesopelagic
3.Bathypelagic
4.Abyssopelagic
5.Hadopelagic
Sunlight, oxygen, and temperature decrease with depth while pressure increases. The organisms
in each zone have adapted to live in these conditions.
Epipelagic
The epipelagic zone extends from the ocean's surface down to about 200 meters (650 feet). This
region is called the euphotic zone (sunlight zone) because sunlight exposure allows the
proliferation(rapid increase)of photosynthetic organisms, like phytoplankton. Currents and wind
constantly mix the water, keeping it relatively warm and well-oxygenated. A sharp drop in water
temperature called a thermocline starts at the lower boundary of the epipelagic zone. The
thermocline marks the transition into the mesopelagic zone.
Mesopelagic
The mesopelagic zone, extending from depths of about 200 meters (650 feet) to 1,000 meters
(3,300 feet), is cooler and darker than the epipelagic zone. It is often called the disphotic zone
(twilight zone) because of its limited sunlight. While organisms may be able to see in the available
light, there is insufficient sunlight for photosynthesis. The lack of photosynthesis, along with the
reduced effects of winds and surface currents, means the water contains less oxygen at this level
than it does at the surface.
Many mesopelagic organisms produce light through a chain of chemical reactions called
bioluminescence. Another adaptation is vertical migration, in which organisms move higher in
the water column at night to find food and move to deeper water during the day to avoid
predators.
Bathypelagic
The bathypelagic zone extends from about 1,000 meters (3,300 feet) to 4,000 meters (13,100
feet) below the surface. Scientists call it the aphotic zone (midnight zone) because it is entirely
devoid of sunlight. Bioluminescent organisms are the only light source. The bathypelagic zone is
very cold, with a nearly constant temperature of 4℃ (39.2℉). There is less life in this zone, but
the organisms living there are adapted to cold temperatures, extreme pressure, and total
darkness. Some better-known bathypelagic zone dwellers include dumbo octopuses,
anglerfishes, and lanternfishes.
Abyssopelagic - This zone starts from around 4000 meters. Very few creatures can reside in cold
temperatures, high pressure, and complete darkness. Species found in this zone are several
species of squid, swimming cucumber, sea pig, and sea spider. Most of the species living here are
transparent and eyeless. The reason being this evolution is the total lack of light.
Hadopelagic - This is the deepest part of the ocean lying within oceanic trenches. The zone is
found from a depth of 6000 to 11000 meters. Most of the hadal habitat is found in the Pacific
ocean.
Benthic Division
“Benthic” word comes from the Greek word benthos, meaning “deep of the sea.” Zone,
meanwhile, comes from the Greek word zone, meaning “belt,” or “girdle.”
Divisions of Benthic Zone
Benthic ecosystems in the sea are separated into 2 groups based on their depth:
1. The nearshore or Littoral system and 2. Deep sea system.
Littoral system extend less than 200 m) which is further divided into two zones:
(A) Eulittoral zone and
(B) Sub littoral zone.
Eulittoral zone includes shore and beach areas which is further divided into three sub zones
which are:
(A) Eulittoral zone:
(a) Supratidal sub zone: (Splash/Arid zone) Supralittoral zone—above high-tide lines influenced
by ocean activities during storm or it covered from sea water during highest high tides of spring
tide.
(b) Intertidal sub zone: it is consider as Beach area. It is the region of high-tide mark to low-tide
mark and it effected twice or once in a day by tidal action.
(c) Sub tidal sub zone: Usually covered from sea water but exposed only in Lowest low tides of
Spring tide.
B. Sub Littoral Zone: The floor of this zone is always covered from sea water. Highly productive
area of Benthic division. Usually the continental shelf area represent the floor of this zone.
2. Deep sea system:
Deep Benthic Zones consist on-
a. Bathyal
b. Abyssal and
c. Hadal zones.
(A) Bathyal zone
Depth Range:(200 to 2,000 m)
The continental slopes area of sea floor are usually called Bathyal zones, usually in the range of
300-2000m;
Bathyal fauna reflect the generally narrow ranges of temperature and salinity that occur. At
Bathyal depths, currents are exceedingly slow, and in many areas bathyal waters deeper than
1,000 m (3,280 feet) are essentially stagnant, resulting in low oxygen concentrations and
impoverished faunal levels.
(B) Abyssal zone
Depth Range: (2,000 to 6,000 m)
The term 'abyssal plain' refers to a flat region of the ocean floor, usually at the base of a
continental rise, where slope is less than 1:1000. It represents the deepest and flat part of the
ocean floor lying between 4000 and 6500 m deep in the U.S. Atlantic Margin.
The abyssal zone, due to its depth, is an extremely demanding environment for living beings: it is
an aphotic region, i.e. it lacks light; the temperature ranges between 0 ºC and 3 ºC; there is a
shortage of nutrients, which makes it difficult for the species that inhabit it to feed and grow;
The ocean bottom or abyssal plain is the Abyssal zone (covering perhaps half of the entire
planet.
( C ) Hadal zone
Depth Range:(over 6,000 m).
The area of deep trenches (about 6000m down to 11,000m such as (Mariana and Phillipine
Trenches) are sometimes called the Hadal zone. These have been little explored, In most areas,
the ocean floor lies 4,000 to 6,000 meters (13,000 to 20,000 feet) below the surface, but deep
ocean trenches can extend this depth to 11,000 meters (36,000 feet). Walls of trenches are steep
and descend through a gradient of depths and pressures, creating a variety of habitats along the
slope.
The region extending from 6,000 to 11,000 meters is called the hadal zone after Hades, the Greek
god of the underworld. This zone occurs only in trenches.
The hadal zone is characterized by extreme depth and pressure, temperatures that hover just
above freezing, and complete darkness—at least in (sence) or in terms of light from the sun.
Bioluminescence allows organisms in the ocean depths to communicate.
Basic characteristics of Benthic division:
The benthic zone is the lowest ecological zone in a water body, and usually involves the sediments
at the seafloor. These sediments play an important role in providing nutrients for the organisms
that live in the benthic 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. The benthic zone is a unique ecosystem, and many of the
organisms that live in it cannot be found elsewhere in the water column, especially in the deep
ocean. The surface of most Benthic areas is consist on mud and organic ooze, though some
bathyal slopes are rocky.
Most life here must also cope(deal effectively with something difficult.) with low food supply,
and again most food chains start with detritus and bacteria. The most common fishes are the rat
tails or grenadiers; the most common large invertebrates are echinoderms such as sea
cucumbers, seastars; but there are many other animals such as sea anemones, sponges, molluscs,
crabs, sea spiders (pycnogonids), burrowing worms of many types; etc are recorded.
Echinoderms such as sea cucumbers have been seen at 10,200m depths.
The End
