levels of marine zones

1. BY:
MARIYAM NAZEER AGHA
KUD NO: 15S14233
DEPT. OF STUDIES IN ZOOLOGY
GOVT. ARTS AND SCIENCE COLLEGE,

2. Contents Introduction
 Zonations of sea
 Pelagic zone
 Benthic zone
 Classification of marine biota

3. Introduction
 The marine ecology is diversified and different from other
ecology.
 Marine environment can be divided into some distinct zones
and these are called zonations of marine environment.
 These zones are determined by a number of factors such as
tidal range, individual species range or a combination of the
two.
 The tides are very important which affects turbidity.
 The number and the abundance of various organisms vary from
zone to zone such as in the continental shelf area the
biodiversity of aquatic organisms is most comparing to other
zones .

4. Zonations of sea
 The marine environment can be
divided into two zones:
 Pelagic zone
 The word pelagic is derived
from ancient Greek pelagos
which means open sea. The
pelagic zone occupies 1330
million cubic miles.
 Benthic zone
 The benthic zone is the
ecological region at the lowest
level of a body of water such as
an ocean or a lake, including the
sediment surface and some sub-
surface layers. Organisms living
in this zone are called benthos.

5. Pelagic zone
 This is the part of the ocean extending from the low tide mark with a
relatively shallow depth extending to about 200 meters. The neritic zone has
generally well oxygenated water, low water pressure and stable water
temperature. Zooplankton, free floating creatures ranging from microscopic
foraminifera are to small fish and shrimps live in this zone.
 Palegic zone is sub – divided into:
 Based on the range in depth
 Epipelagic (sunlit)
 Mesopelagic (twilit)
 Bathypelagic (midnight)
 Abyssopelagic (lower midnight)
 Hadopelagic
 Based upon the depth of light penetration
 Photic zone
 Disphotic zone
 Aphotic zone

6. Based on the range in depths
 Epipelagic (sunlit): This zone starts from the
surface down to around 200 m. This is the
illuminated zone at the surface of the sea where
there is enough light for photosynthesis .Nearly
all primary production in the ocean occurs here.
 Mesopelagic (twilit): This zone starts from 200
meters down to 1000 m. This mesopelagic zone is
sometimes referred to as mid water zone.
Although some light penetrates here, it is
insufficient for photosynthesis.
 Bathypelagic (midnight): From 1000 meters
down to 4000 m. This depth the ocean is pitch
black. Apart from occasional bioluminescent
organisms such as lantern fish, there is no living
plant life .
 Abyssopelagic (lower midnight): From 4000
meters down to6000 m. The water temperature is
near freezing and there is no light at all. This zone
is mostly unknown and very few species are
known to live here .
 Hadopelagic
 This zone extends from 6000 m to the ocean
bottom. These areas are mostly found water
trenches and canyons.

7. Based on the light penetration
 Photic zone: The photic zone is the depth of the
water of ocean that is exposed to sufficient
sunlight for photosynthesis to occur.
Typical euphotic depths vary from only a centime
ter in highly turbid eutrophic lakes, to around 200
m in the open sea. It also varies with the seasonal
changes of turbidity. The number of various kinds
of phytoplankton is very higher in this zone.
 Disphotic zone: This is the zone start from 200 m
to 700 m. In the disphotic zone small amount of
sunlight penetrate. The rate of photosynthesis is
very low in this layer. Turbidity is an important
factor which determines the turbidity.
 Aphotic zone: This is the zone of ocean where
there is no sunlight. Consequently,
bioluminescence is essentially the only light
found in this zone. Most food comes from dead
organisms sinking to the bottom of the ocean
from overlaying water. The temperature is very
low.
Phytoplanktons in photic zone
Swordfish in disphotic zone
Biolumininescent angler fish
in aphotic region

8. Benthic zone
 The benthic region of the ocean begins at the shore line and extends downward
along the surface of the continental shelf out to sea.
 The continental shelf is a gently sloping benthic region that extends away from the
land mass. At the continental shelf edge, usually about 200 meters deep, the gradient
greatly increases and is known as the continental slope.
 The continental slope drops down to the deep sea floor. The deep-sea floor is called
the abyssal plain and is usually about 4,000 meters deep. The ocean floor is not all
flat but has submarine ridges and deep ocean trenches known as the hadal zone.
 Depending on the water body, the benthic zone may include areas that are only a few
inches below water, such as a stream or shallow pond, or may be at the bottom of an
ocean below a 4,000 meter (13,000 foot) column of water.
 Benthic habitats are very diverse, depending upon their depth and location and have
distinct biological, physical, and geochemical characteristics . The superficial layer
of the soil lining the given body of water is an integral part of the benthic zone, as it
influences greatly the biological activity that takes place there.
 Examples of contact soil layers include sand bottoms, rock outcrops, coral, and bay
mud.

9. Classification of marine biota
 Marine biota can be classified broadly into those organisms
living in either the pelagic environment (plankton and
nekton) or the benthic environment (benthos).
 Some organisms, however, are benthic in one stage of life
and pelagic in another.
 Producers that synthesize organic molecules exist in both
environments.
 Single-celled or multi - celled plankton
with photosynthetic pigments are the producers of the
photic zone in the pelagic environment.
 Typical benthic producers are microalgae (e.g., diatoms),
macroalgae (e.g., the kelp Macrocystis pyrifera), or sea
grass (e.g., Zostera).

10. Plankton Plankton are the numerous, primarily microscopic inhabitants of the
pelagic environment. They are critical components of food chains in
all marine environments because they provide nutrition for the
nekton (e.g., crustaceans, fish, and squid) and benthos (e.g., sea
squirts and sponges). They also exert a global effect on the biosphere
because the balance of components of the Earth’s atmosphere
depends to a great extent on the photosynthetic activities of some
plankton.
 Plankton range in size from tiny microbes (1 micrometre [0.000039
inch] or less) to jellyfish whose gelatinous bell can reach up to 2
metres in width and whose tentacles can extend over 15 metres.
 The plankton include a wide variety of organisms such as algae,
bacteria, protozoans, the larvae of some animals, and crustaceans.
 Phytoplankton carry out photosynthesis and are the producers of the
marine community; zooplankton are the heterotrophic consumers.
 Zooplanktons are greater than 0.05 millimetre in size.

11. Nekton
 Nekton are the active swimmers of the
oceans and are often the best-known
organisms of marine waters. Nekton
are the top predators in most marine
food chains.
 The vast majority of nekton
are vertebrates (e.g., fishes, reptiles,
and mammals), mollusks,
and crustaceans. The most numerous
group of nekton are the fishes, with
approximately 16,000 species.
 Nekton diversity is greatest in tropical
waters, where in particular there are
large numbers of fish species.
 The largest animals on the Earth,
the blue whales (Balaenoptera
musculus), which grow to 25 to 30
metres long, are members of the
nekton.

12. Benthos
 Organisms are abundant in surface
sediments of the continental shelf and
in deeper waters, with a great diversity
found in or on sediments.
 On many sediments in the photic zone,
however, the only photosynthetic
organisms are microscopic benthic
diatoms.
 Benthic organisms can be classified
according to size.
The macrobenthos are those organisms
larger than 1 millimetre.
 Organisms between 0.1 and
1millimetre constitute the meiobenthos
.
 The microbenthos are those organisms
smaller than 1 millimetre; they include
diatoms, bacteria, and ciliates.