AN ASSIGNMENT ON THEZONATION OF MARINE

ENVIORNMENT

COURSE CODE:CMF-223

COURSE TITLE:FISHERIES

OCEANOGRAPHY

SUBMITTED BY SUBMITTED TO

MD. MOSSAROF HOSSAIN ID: 1203071, 1103004, 1103016, 1103052, 1103053, 1103057, 1103064 Lecturer

Dept. of Coastal and Marine Fisheries

B. Sc. Fisheries (Hons.) LEVEL: 2; SEMESTER:2; SESSION: (2011-12)

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DEPARTMENT OF COASTAL AND MARINEFISHERIES

SYLHET AGRICULTURAL UNIVERSITY, SYLHET-3100

IntroductionThe term marine is for things relating to the bay, sea or oceanetc. Generally the marine environment is characterized by thesalty water and tides .The marine ecology is diversified anddifferent from other ecology .Marine environment can be dividedinto some distinct zones and these is called zonation of marineenvironment .These zones are determined by a number of factorssuch as tidal range , individual species range or a combinationof the two .The tides are very important which affectsturbidity .The number and the abundance of various organisms varyfrom zone to zone such as in the continental shelf area thebiodiversity of aquatic organisms is most comparing to otherzones .In the ocean a great diversity of strange and bizarrefishes and organisms can be found. Some zones are economicallyand environmentally very important while some are unknown orhaving little knowledge .In the deeper region the water pressureis very high with no light penetration. Amongst the zones ofocean continental shelf is very important because of its higherproductivity.

Zonation of marine environment

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The sea or ocean of the sea is divided into various divisionswhich is called zonation of sea

The marine environment can be divided into two zones:

•Pelagic zone

• Benthic zone

Pelagic zone The word pelagic is derived from ancient Greek pelagos whichmeans open sea. The pelagic zone occupies 1330 million cubicmiles .Fish that live in pelagic area are called pelagic fish.

The pelagic environment is divided into the

Neritic zone This is the part of the ocean extending from the low tide mark tothe edge of the continental shelf with a relatively shallow depthextending to about 200 meters. The neritic zone has generallywell oxygenated water, low water pressure and stable watertemperature. Zooplankton, free floating creatures ranging frommicroscopic foraminifera are to small fish and shrimps live inthis zone.

Oceanic zone The oceanic zone begins in the area off shore where the watermeasures 200 meters deep or deeper .It is the region of open seabeyond the edge of continental shelf and includes 65% of theoceans completely open water .shelf break, deep ocean water.

Because of the range in depths, the oceanic zone issubdivided further into the:

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Epipelagic (sunlit) This zone starts from the surface down to around 200 m. This isthe illuminated zone at the surface of the sea where there isenough light for photosynthesis .Nearly all primary production inthe ocean occurs here. With the light heat comes and this heat isresponsible for the wide range of temperature .Organisms found inthis zone are plankton, seaweeds, jellyfish etc.

Mesopelagic (twilit) This zone starts from 200 meters down to 1000 m .The name stemsfrom the Greek meson means middle .This mesopelagic zone issometimes referred to as mid water zone .Although some lightspenetrates this second layer, it is insufficient forphotosynthesis. Some creatures which live in this zone arebioluminescent .Organisms that are available here are squid,cuttlefish, wolfish, swordfish etc. A great diversity of strangeand bizarre fishes can be found here.

Bathypelagic (midnight)From 1000 meters down to 4000 m .The name stems from the ancientGreek bathys means deep. At this depth the ocean is pitch black,apart from occasional bioluminescent organisms such as lanternfish .There is no living plant life .Most species depends on preyfor food e.g. Giant squid. Most of the animals that live at thisdepth are black or red in color due to the lack of light.

Abyssopelagic (lower midnight)

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The name is derived from the Greek abyssos means bottomless andfrom 4000 meters down to 6000 m. The water temperature is nearfreezing and there is no light at all. This zone is mostlyunknown and very few species are known to live here .The abyssalplain is covered with soft sludge composed of dead organisms fromabove.

HadopelagicThis zone extends from 6000 m to the ocean bottom. The name isderived from the realm of hades, the underworld in Greekmythology .These areas are mostly found water trenches andcanyons. The deepest point in the ocean is located in the Marianatrench off the coast of japan at 35797 feet. The temperature ofthis is zone is above freezing and the pressure is an incredibleeight tons per inch .This zone is mostly unknown and very fewspecies are known to live here .However many organisms live inhydrothermal vents in this zone. These deep zone is where some ofthe most bizarre and fascinating creatures in the sea can befound.

The oceanic zone can also be divided into different zonesbased upon depth of light penetration:

Photic zoneThe photic zone is the depth of the water of ocean that isexposed to sufficient sunlight for photosynthesis tooccur .Typical euphotic depths vary from only a centimeter inhighly turbid eutrophic lakes, to around 200 m in the opensea .It also varies with the seasonal changes of turbidity. The

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number of various kinds of phytoplankton is very higher in thiszone.

Disphotic zone This is the zone start from 200 m to 700 m .In the disphotic zonesmall amount of sunlight penetrate .The rate of photosynthesis isvery low in this layer .Turbidity is an important factor whichdetermine the transparency.

Aphotic zone This is the zone of ocean where there is no sunlightconsequently bioluminescence is essentially the only light foundin this zone .Most food comes from dead organisms sinking to thebottom of the ocean from overlaying water. The temperature isvery low.

Benthic zoneThe zone of the ocean bottom is called benthic zone. The zone canbe divided as follows:

Intertidal zoneThe zone between high tide and low tide is called intertidalzone. Most of the area of this zone is exposed to the air duringlow tide.

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Fig: Zonationof marine environment.

Continental marginThe continental shelf, rise and slope together are calledcontinental margin.

Continental shelf The continental shelf is shallow, near horizontal seafloorextension from the shoreline to the upper continental slope .Thisshelf forms the shallow margin of each deep ocean basin .It isone of the most productive zone of the ocean .This area is also

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commercially very important. Continental shelf varies with width.The bottom is composed of fine sediments like sand and silt.

Shelf break The steepening of bottom that marks the seaward limit of thecontinental shelf

Continental slopeThe continental slopes begin at the shelf break and plungdownward to the great depths of the ocean basin proper.

Continental riseMany continental slopes end in gently sloping, smooth surfacedfeatures called continental rise.

Conclusion Organisms are not evenly distributed in marine environment .Toknow about the abundance and the distribution of variousorganisms zonation of sea or ocean is very important .The oceancan be divided into several zones. Each zone has distinctcharacteristics with different organisms.

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References:

• http://www.cbd.int/

• http://www.un.org/

• http://www.unep.org/

• http://www.centerforoceansolutions.org/

• http://who.int/en/

• Department of marine fisheries, University of Washington, Box 351800, Seattle, WA 98195-1800, USA.

• Centre for Mathematical Biology, Department of Biological Sciences and Department of Mathematical & Statistical Sciences, University of Alberta, Canada.

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