Australia‟s Great #Barrier #Reef sees largest coral die-off ever :

1. A #mass bleaching event on the #Great Barrier #Reef this year killed more corals than ever before, sounding the alarm over the delicate #ecosystem.

2. The 2,300-kilometre long #reef — the world‟s biggest — suffered its most severe bleaching in recorded history, due to warming sea temperatures during March and April, with the #northern third bearing the brunt.

3. Follow-up underwater surveys, backing earlier aerial studies, have revealed a 700-kilometre stretch of reefs in the less-accessible north lost two-thirds of shallow-#water corals in the past eight to nine months.

4. Most of the losses in 2016 have occurred in the northern, most-pristine part of the #Great Barrier #Reef.

5. This region escaped with minor damage in two earlier bleaching events in 1998 and 2002, but this time around it has been badly affected.

6. Further south over the vast #central and southern #regions, including major tourist areas around #Cairns and the Whitsunday #Islands, there was a much lower toll.

7. Bleaching occurs when abnormal #environmental conditions, such as warmer sea temperatures, cause corals to expel tiny #photosynthetic algae, draining them of their colour.

8. #Algae are vital to the coral, which uses the #organic products of photosynthesis to help it grow.

9. The loss of algae makes the host vulnerable to #disease and means it will eventually die.

10. However, coral can recover if the water temperature drops and the #algae are able to recolonise them.

11. #Environmentalists blame the burning of fossil fuels for global warming and repeated calls for #Australia to abandon coal mining to help prevent further bleaching disasters.

12. A credible plan to protect the reef must address #climate change and start with a ban on new coal mines.

13. Canberra insists it is doing more than ever to safeguard the reef, which is also under pressure from farming run-off, development and the coral-eating crown-of-thorns starfish, committing more than #Aus$2.0 billion (US$1.50 billion) over the next decade.

Long recovery:-

1. #Scientists estimate the #northern region, which teems with marine life, will take at least 10-15 years to regain lost #corals, but are concerned that a fourth major bleaching event may occur before that, hampering the recovery. The reef studies centre warned earlier this year that if greenhouse gas levels keep rising, similar events would be the new normal, occurring every two years by the mid-2030s.

2. Given #reefs need so long to recover from severe bleaching.

3. That study noted climate change had added 1.0 degree #Celsius of warming to #ocean #temperatures off the Queensland coast in March, when #corals were first seen turning white.

4. The good news is the #southern two-thirds of the reef has escaped with minor damage.

5. On average, six percent of bleached #corals died in the central region in 2016, and only one percent in the south. The corals have now regained their vibrant colour, and these #reefs are in good condition.

#Coral #Reefs?

1. #Coral #reefs are marine ridges or mounds, which have formed as a result of the deposition of calcium carbonate by living organisms, predominantly corals, but also a rich diversity of other organisms such as #coralline algae and shellfish.

2. An individual coral is known as a #polyp, a very small and simple organism consisting mostly of a stomach topped by a tentacle-bearing mouth.

3. The #polyps extend their tentacles at night to sting and ingest tiny #organisms called plankton and other small creatures.

4. Thousands of identical polyps live together and form a coral colony. Each polyp excretes a #calcium carbonate exoskeleton beneath it and, over long periods of #time, the skeletons of many #coral colonies add up to build the structure of a coral #reef.

5. Many other species – fish, invertebrates, #algae and #microorganisms – make their homes on and around this reef. #Reefs only occur in shallow areas that are reachable by sunlight because of the relationship between #coral and algae.

6. #Coral lives a symbiotic life. Inside the sac of each #coral polyp lives one-celled algae called #zooxanthellae. The algae gives off #oxygen and other nutrients that the coral polyp needs to live and in return the polyp gives the algae carbon dioxide and other substances the #algae needs. That is why coral reefs grow so near the surface of the water where it is the sunniest--the algae need sunshine for #photosynthesis.

7. In addition to providing corals with essential nutrients, #zooxanthellae are responsible for the unique and beautiful colors of many stony #corals. Sometimes when corals become physically stressed, the polyps expel their algal #cells and the colony takes on a stark white appearance. This is commonly described as “coral bleaching”.

#Coral Reef Formation :

1. #Coral reefs begin to form when free-swimming coral larvae attach to submerged rocks or other hard surfaces along the edges of islands or continents. As the #corals grow and expand, reefs take on one of three major characteristic structures —fringing, barrier or atoll.

                  

1. #Fringing reefs: They are the most common, project seaward directly from the shore, forming borders along the shoreline and surrounding islands.

2. #Barrier reefs: Grow at border shorelines, but at a greater distance. They are separated from their adjacent land mass by a lagoon of open, often deep water.

3. #Atoll: If a fringing reef forms around a volcanic island that subsides completely below sea level while the coral continues to grow upward, an atoll forms. Atolls are usually circular or oval, with a central lagoon.

Condition for #Coral Growth:-

1. For the growth and development of #corals the surface temperature of the #ocean must be above 20°C. #Corals cannot live if the temperature of the #sea water falls below this.

2. The #water must be shallow, with a depth not exceeding 25-30 fathoms. With increasing depth, the amount of calcium as well as the #temperature of water goes on decreasing, so that the coral polyps and other sea creatures which live on calcium carbonate do not thrive. That is why the reef building corals live in shallow #waters and on the surface of the #seas.

3. The #water must be normally #saline, and, therefore, along the ocean margins where the water becomes fresh by the inflow of rivers, #reef building corals do not grow and develop.

4. #Corals need clear water that is free from abundant sediments. That is why coral #reefs cannot develop where rivers enter the sea or where wave-erosion causes muddy coastal water.

5. There must be adequate food supply to nourish the abundant life of the #coral reef. The most favourable condition for this purpose is the presence of continuously flowing ocean currents which provide to the stationary reef building organisms the much needed food supply.

6. For example, extensive coral reefs are found on the east coasts of #Australia,Central #America, and #Africa, which are washed by warm ocean currents flowing along them. On the contrary, corals are found only in scattered patches on the west #coasts of these continents.

7. If the salinity of the ocean #water is very high, the lime content is bound to be low, which is not favourable for the growth of corals. Therefore the average salinity ranging from 27% to 40% is ideal for the proper growth of #corals and other #reef forming creatures.

8. The most essential prerequisite for the formation of coral reefs is the presence of sub-marine platforms which must lie near the sea shore, or should be attached to some islands. The depth of water on such platforms should not exceed 50 fathoms. Remember that the corals build their permanent colonies only on these platforms.

9. #Corals cannot live for long out of water, and are therefore, rarely found above the low-tide level. On the other hand, their growth is retarded at depths much exceeding 25 or 30 fathoms.

10. #Corals need clear oxygenated water with sufficient supplies of microscopic life as food.

11. Since food supplies are plentiful on the seaside of a growing reef, the #corals tend to grow.

Main threats to #coral reefs

1. Destructive fishing practices
2. Overfishing
3. Careless tourism
4. Pollution o Sedimentation
5. #Coral mining
6. #Climate change

Likely impacts of climate change to coral reefs:

1. #Coral Bleaching
2. Slower #Coral Growth
3. Physical Damage to #Coral Reefs
4. #Coral Mortality

Steps that can be taken to protect coral reefs from climate change:

1. Create Effective Marine Protected Areas (#MPAs)
2. Lessen Other Pressures on #Coral #Reefs
3. Identify Ways To Adapt
4. Protect and Enhance #Ecosystems That Absorb
#Greenhouse Gases

            

Distribution of #Coral #Reef in India :

1. #Palk Bay o The Gulf of Mannar
2. #Andaman and Nicobar Group of Islands
3. The #Gulf of Kutch o West Coast of India
4. The #Lakshadweep Islands