Coral Reefs Part 1: Blocking out the sun

Coral reefs are some of the most spectacular natural wonders anyone can see. The colours, species and types of fish are breath-taking; the vibrancy, colours and structures of corals found in them is awe-inspiring. However, these complex structures have specific requirements to survive as anyone would expect. Some of these are fluctuating because of the dreaded, yet inevitable global warming. A case in point, the Great Barrier Reef. With the threat of global warming mounting any other attack from a different direction could be catastrophic. And what is this new less known villain? Silt. The removal of fine sediment from the nearshore allows ships closer to port, that is then dumped near the reef, which ultimately drifts back choking it to death, restricting light and starving it of food.

Clear Clean Water

>Water that is low in fine sediment is an essential box tick for many reef systems. It blocks sunlight from penetrating the water and prevents the coral photosynthesising. The sediment also makes it difficult for the polyps to filter feed and perform gas exchange. Over short periods of time, the coral can survive, but consistent barrages of fine sediment can suffocate a reef. The result of rapid expulsion of fresh water from the land, taking with it sediments to the sea. This is issue is affecting the Great Barrier Reef because huge jungle expanses have been reduced for farmland and cities. Along with the sediments are farmland chemicals, which when added to the reef ecosystem cause severe imbalances. This high flux causes in-balances (subject of another article) as reefs naturally survive with low concentrations of nutrients.


Reef that is suffering from high rates of sedimentation. Notice fine silt covering seabed and corals.


As corals consist of algae or Zooxanthellae, sunlight is vital in giving the coral food. The coral polyps, which are the animal part of the coral that filter feed the water removing small animals named zoo-plankton. There are examples of deep water corals but there physiology doesn’t rely on the sun’s energy for photosynthesis. However, as explained in the previous section clean water is vital, as without it they can’t produce food from photosynthesis. Starvation can then take hold, destroying entire reef ecosystems, if there is a constant outflow of fine material like from the dredging around the barrier reef. With sediment being moved and discarded offshore on a daily basis, with most drifting on the reef.



Beautiful, yet delicate coral reef structures under threat from global warming, poor water quality, sea level rise and acidification

Dredging along the Great Barrier Reef

With all these external threats to many reefs (excluding overfishing as is a whole different topic), with a focus on the Great Barrier Reef, it is a relief that the banning of sediment extraction and dumping on the Great Barrier reef is in place in Australia. There was original legislation, preventing dredgers offloading sediment on the reef due to the problems and issues highlighted above. Boats could unload within a few kilometres, which would quickly wash over the reef engulfing it. With tides keeping it in suspension it could be hours or days before it is moved, resulting in the reef starving to death in just a few days. What is the goal? Just to remove sediment so the water is deep enough to allow humongous floating cities stocked with coal into port to generate energy. It seems crazy that not only is the cargo they are bringing in destroying the reef, either by dredging or impacts of boats on to the reef, but the global warming stimulus of fossil fuels, coal, which is causing the greatest impact, global warming, but is the most difficult to solve, the subject for part 2.

Coral Reefs Part 2

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I am a trained geologist who has a passion for conservation and working with wildlife. I write articles that interest me and that I am passionate about using skills and knowledge to highlight issues related to climate change. I don’t write articles for views, I write them to change views.

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2 Responses

  1. 17th November 2015

    […] Coral Reefs Part 1 […]

  2. 25th November 2015

    […] Coral Reefs Part 1 […]

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