zonations of sea and ecological classification of marine biota

levels of marine zones

1. Explain Z onations of sea and ecological classifications of freshwater animals BY: MARIYAM NAZEER AGHA KUD NO: 15S14233 DEPT. OF STUDIES IN ZOOLOGY GOVT. ARTS AND SCIENCE COLLEGE, KARWAR

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): F rom 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 centimeter 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 .