COASTAL ZONATION
The term coastal zone means the coastal waters (including the lands therein and thereunder) and the adjacent shore lands (including the waters therein and thereunder), strongly influenced by each and in proximity to the shorelines of the several coastal states, and includes islands, transitional and inter-tidal areas, salt marshes, wetlands, and beaches.
CLASSIFICATION ON THE BASIS OF SUBSTRATUM DEPTH AND SUBMARINE FEATURES:
A. OCEAN BASIN
1. CONTINENTAL MARGINS:
These are the edges of the land masses present bellow the
ocean surface.
- Continental Shelf – It is a nearly flat land border of varying with that gently slopes towards the ocean basin. Maximum depth is 130 m. The average width is 65 km & varies from few kilometers to 100 km.
- Continental slope – The continental shelves from shell break steepens into continental slope and extends up to the ocean basin floor. They are often cut by submarine canyons
- Continental Rise – At the base of the steep continental slope there may be a gentle slope formed by accumulation of sediments leading to the formation of continental rise. It is well developed in Atlantic and Indian Ocean, narrow or almost nonexistent in Pacific Ocean.
2. OCEAN BASIN FLOOR:
The floor extends seawards from continental rise or the continental margins and includes the abyssal plains, oceanic rises, seamounts & trenches.
- Abyssal Plain – Located at the base of continental rise & are flat plains having gradient less than 1: 1000. they are formed due to an even deposition of sediments from continental rise carried down by turbidity currents.
- Oceanic Rises – Its refer to rather isolated areas which are elevated above the abyssal floor & are distributed sporadically on the ocean basin floor. Elevation may have varied as high as 1200 m. e.g. Bermuda Islands.
- Seamounts – These are isolated peaks which rise several thousand meters above the sea floor. They are volcanic in origin.
- Trenches – These are narrow, long depressions in ocean floor which are over 6100 m deep. e.g. Mariana Trench (11,000m deep) of Western North Pacific. These are invariably associated with volcanoes and are believed to be formed by down wrapping of oceanic crust beneath the continental crust.
The deepest recorded oceanic trenches measure to date is the Mariana Trench, near the Philippines, in the Pacific Ocean at 10,924 m (35,838 ft). At such depths, water pressure is extreme and there is no sunlight, but some life still exists. Small flounder (family Soleidae) fish and shrimp were seen by the American crew of the bathyscaphe Trieste when it dove to the bottom in 1960.
Other notable oceanic trenches include Monterey Canyon, in the eastern Pacific, the Tonga Trench in the southwest at 10,882 m (35,702 ft), the Philippine Trench, the Puerto Rico Trench at 8,605 m (28,232 ft), the Romanche Trench at 7,760 m (24,450 ft), Fram Basin in the Arctic Ocean at 4,665 m (15,305 ft), the Java Trench at 7450 m (24,442 ft), and the South Sandwich Trench at 7,235 m (23,737 ft).
Marine life also flourishes around seamounts that rise from the depths, where fish and other sea life congregate to spawn and feed. Hydrothermal vents along the mid-ocean ridge spreading centers act as oases, as do their opposites, cold seeps. Such places support unique biomes and many new microbes and other life forms have been discovered at these locations
B. OCEAN WATER MASS
1. NERITIC ZONE:
Shallow water pelagic zone extends from intertidal zone to the edge of continental shelf. In fact, the neritic zone encompasses the coastal waters having average depth of 200 m.
2. OCEANIC ZONE: The water mass beyond the continental shelf seawards covering the deep abyssal plain constitute the oceanic zone. The pelagic provinces consists of
- EPIPELAGIC ZONE – surface to 200 m depth
- MESOPELAGIC ZONE – 200 to 1, 000 m depth
- BATHYPELAGIC ZONE – 1, 000 TO 4, 000 m depth
- ABYSSOPELAGIC ZONE – anything bellow 4, 000 m
CLASSIFICATION ON THE BASIS OF LIGHT PENETRATION
1. PHOTIC ZONE: The zone where sunlight can penetrate. It is usually restricted to 200 m from the surface. Productivity is more with huge population of primary producers and planktons. The zone may further classified into a) Euphotic zone (brightly illuminated, 0-80m) and b) Disphotic zone (twilight, 8-200m)
2. APHOTIC ZONE: It is deeper, lightless zone of the ocean bellow 200m.
CLASSIFICATION OF BENTHIC ENVIRONMENT
1. SUBNERITIC PROVINCE: The benthic zone from the highest high tide line at the land-sea interface to a depth of 200 m seaward, including mostly the continental shelf.
2. SUBOCEANIC PROVINCE: The entire benthic environments bellow 200 m depth.
CLASSIFICATION OF BENTHIC ENVIRONMENT ON THE BASIS OF DEPTH
SUPRA LITTORAL ZONE: The zone above the highest high tide mark. The zone is also known as splash zone.
LITTORAL ZONE OR INTERTIDAL ZONE: The zone where the tide plays. The intertidal area (also called the littoral zone) is where the land and sea meet, between the high and low tide zones. This complex marine ecosystem is found along coastlines worldwide. It is rich in nutrients and oxygen and is home to a variety of organisms. e.g. Sandy beaches, rocks, estuaries, mangrove swamps, coral reefs.
- Spray Zone: Also called the Upper Littoral, the Supra littoral Fringe, the Splash Zone, and the Barnacle Belt. This area is dry much of the time, but is sprayed with salt water during high tides. It is only flooded during storms and extremely high tides. Organisms in this sparse habitat include barnacles, isopods, lichens, lice, limpets, periwinkles, and whelks. Very little vegetation grows in this area.
- High Tide Zone: Also called the Upper Mid-littoral Zone (Upper Eulittoral) and the high intertidal zone. This area is flooded only during high tide. Organisms in this area include anemones, barnacles, brittle stars, chitons, crabs, green algae, isopods, limpets, mussels, sea stars, snails, whelks and some marine vegetation.
- Middle Tide Zone: Also called the Lower Mid-littoral Zone (Lower Eulittoral). This turbulent area is covered and uncovered twice a day with salt water from the tides. Organisms in this area include anemones, barnacles, chitons, crabs, green algae, isopods, limpets, mussels, sea lettuce, sea palms, sea stars, snails, sponges, and whelks.
- Low Tide Zone: Also called the Lower Littoral Zone (Sublittoral Fringe). This area is usually under water - it is only exposed when the tide is unusually low. Organisms in this zone are not well adapted to long periods of dryness or to extreme temperatures. Some of the organisms in this area are abalone, anemones, brown seaweed, chitons, crabs, green algae, hydroids, isopods, limpets, mussels, nudibranchs, sculpin, sea cucumber, sea lettuce, sea palms, sea stars, sea urchins, shrimp, snails, sponges, surf grass, tube worms, and whelks.
SUBLITTORAL ZONE:
This is the shallow sub tidal zone below the lowest low water within continental shelf – it includes the inner sub littoral zone up to the depth of 50 m. and outer sub littoral zone with 200 m depth.
- BATHYAL ZONE: 200 m to 4000 m deep benthic provinces come under this zone. Its generally corresponds to continental slope.
- ABYSSAL ZONE: The benthic province between 4000 m to 6000 m depth range. It covers more than 60% of the benthic environment.
- HADAL ZONE: Below 6000 m up to deepest trenches.
