- Coral reefs –
- Formed due to the accumulation and compaction of skeletons of lime secreting organisms (Coral polyps).
- Found mainly in the tropical oceans and seas as they require high mean annual temperature. (200 C to 250 C)
- Do not lies in deep sea water, due to lack of sunlight and oxygen.
- On the basis of nature, mode of occurrence and shape, Coral reefs are classified into three types:
- Fringing reefs.
- Develops along continental margins or along the islands.
- Seawards slope is steep and vertical, while landwards slope is gentle.
- Runs as a narrow belt of about 0.5 km to 2.5 km width.
- Usually attached to the coastal land but occasionally they are separated from the shore by a shallow and narrow lagoon (Boat channel).
- Example: Near Rameshwaram in the Gulf of Mannar, etc.
- Barrier reefs.
- Largest coral reefs off the coastal platform, but parallel to them.
- A broad lagoon develops in between the reef and the shore.
- Are hundreds of km long and a few km wide.
- Example: Great Barrier Reef of Australia (largest), etc.
- Atoll.
- A reef of narrow growing corals of horse shoe shape and crowned with palm trees.
- Partly or completely encloses a lagoon.
- Formed around an island or in an elliptical form on a submarine platform.
- Example: Funafuti atoll of Ellice Islands, etc.
- Fringing reefs.
- Coral bleaching – When chorals are stressed by changes in conditions such as temperature, light or nutrients, they expel the symbiotic algae living in there tissues causing them to turn colourless.
- Salinity –
- Total amount of salts and minerals in grams contained in 1 kg of sea water, expressed as part per thousand.
- Affects marine organism and plant community, also physical properties of ocean such as temperature, pressure, density, waves and currents.
- Average salinity: 35 mg / kg. (35 ppt)
- Average salinity in southern hemisphere > average salinity of the northern hemisphere.
- Iso halines: Represents the salinity distribution on the surface of the sea. (lines joining places having an equal degree of salinity)
- Due to dissolution of rocks of oceanic crust.
- Variation of salinity causes vertical circulation of water.
- More saline water freezes slowly and the boiling point is higher than the fresh water.
- Decreases from equator to poles.
- Highest salinity is near the tropics, because of heavy precipitation in the equatorial region.
| Controlling factor | Relation with salinity |
| Evaporation | Greater evaporation higher the salinity |
| Precipitation | Higher the precipitation lower the salinity |
| Influx of river water | Salinity is reduced at the mouth |
| Atmospheric pressure | Anti cyclonic conditions with stable air and high temperature Increases the salinity of the surface water of the ocean |
| Circulation of oceanic water | Ocean currents affects the spatial distribution of salinity by mixing sea waters |
- Ocean currents –
- Due to the action of breaking waves, wind, Coriolis effect, temperature, salinity, shape and configuration of coast line and the tides (caused by sun and the moon).
- Clockwise in northern hemisphere and anticlockwise in the southern hemisphere.
- Are of two types:
- Warm currents.
- Flows from lower latitude to the higher latitude.
- Cold currents.
- Flows from higher latitude to the lower latitude.
- Warm currents.
- Tides –
- Rises at an interval of approx 12 hrs 26 min.
- The two major types of tides are:
- Spring tides.
- Occurs when earth, moon and sun are in line i.e straight line configuration of the three celestial bodies.
- Sun enhances the gravitational pull of the moon, creating the condition of higher high tides and lower low tides.
- Neap tides.
- When the sun and the moon are at right angles to the earth.
- The sun partially contracts the pull of the moon, producing lower high tides.
- Spring tides.