Coastal Aquaculture and Mariculture

Unit 1 - Fishery Zones and Fishery resources

1.2. Structure of the Earth in the marine environment
While about 70% of the surface of the earth is covered by salt water, freshwater covers only about 1% of the earth's surface. By volume, 97% of all water is in the oceans. The bottom topography of the marine environment includes continental shelf, continental slope, continental rise and abyssal plains among other features.
Intertidal zone
The intertidal zone (also known as the foreshore) is the area that is exposed to the air at low tide and submerged at high tide, for example, the area between tide marks. This area can include many different types of habitats, including steep rocky cliffs, sandy beaches and vast mudflats.
Littoral zone
It refers to the coast of an ocean or sea, or to the banks of a river, lake or estuary. It extends from the high water mark, which is rarely inundated, to shoreline areas that are permanently submerged. It includes the intertidal and sublittoral zones. The littoral zone is bordered by the supralittoral zone, also known as the "spray zone", and the sublittoral zone, which runs to the edge of the continental shelf.
Supra littoral zone (Spray zone)
It is the area above the spring tide line that is regularly splashed, but not submerged by ocean water.
Sublittoral zone
It is the part of the Earth's surface immediately below the intertidal zone and thus permanently covered with seawater. The sublittoral zone is the part of the ocean extending from the low tide mark to the edge of the continental shelf, with a relatively shallow depth extending to about 200 meters.
Continental shelf
The continental shelf is the extended perimeter of each continent and. associated coastal plain. The shelf usually ends at a point of decreasing slope (called the shelf break). The continental shelf and the slope are part of the continental margin. The shelf area is commonly subdivided into the inner continental shelf, mid continental shelf, and outer continental shelf, each with their specific geomorphology and marine biology.
Continental slope
The sea floor below the break is the continental slope. The continental slope is much steeper than the shelf; the average angle is 3°, but it can be as low as 1° or as high as 10°. The slope is often cut with submarine canyons.
Continental rise
It is below the slope and fmally merges into the deep ocean floor, the abyssal plain, but landward of the abyssal plains. Its gradient is intermediate between the slope and the shelf, on the order of 0.5 - 1°. Extending as far as 500 km from the slope, it consists of thick sediments deposited by turbidity currents from the shelf and slope. Sediment cascades down the slope and accumulates as a pile of sediment at the base of the slope, called the continental rise.
Abyssal plain
Abyssal plains are flat or very gently sloping areas of the deep ocean basin floor. They are among the Earth's flattest and smoothest regions and the least explored. Abyssal plains cover approximately 40% of the ocean floor and reach depdts between 2,200 and 5,500 m (7,200 and 18,000 ft). They generally lie between the foot of a continental rise and a mid-oceanic ridge.
The marine environment can be divided into three zones such as

• Pelagic zone
• Benthic zone
• Demersal zone.

Pelagic zone:
The Pelagic zone is the ecological region above the benthic, including the water-column up to the surface. Any water.in the sea that is not close to the bottom is in the pelagic zone. The word pelagic comes from the Greek pelagos, which means open sea. Fish that live in the pelagic zone are called pelagic fish. Pelagic life decreases with increasing depth. In deep water, the pelagic zone is sometimes called the open-ocean zone and can be contrasted with water that is near the coast or on the continental shelf. However in other contexts, coastal water that is not near the bottom is still said to be in the pelagic zone. Profundal zone is a deep zone of a body of water, such as an ocean or a lake, located below the range of effective light penetration. This is typically below the Thermocline. It is a part of the aphotic zone.
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. Marine organisms living in this zone, such as clams and crabs, are called benthos.
Demersal zone:
The demersal zone is just above the bendthic zone. It is the part of the sea or ocean (or deep lake) comprising the water column that is near to (and is significantly affected by) the seabed and the benthos. The demersal zone is just above the benthic zone and forms a layer of the larger profundal zone. Fish that live in the demersal zone are called demersal fish.