Cyclones

Tropical Cyclones

What is a tropical cyclone?

• intense cells of low pressure with a central eye surrounded by a circular wind system
• storm surges, strong winds
• unpredictable directions

What Kind of Damage does it do to coral reefs?

Reef damage varies with the intensity, distance and location of a cyclone. With the right conditions, a cyclone can be catastrophic to a coral communities and its inhabitants.

• Water: The sedimentary processes, salinity levels, and sea levels of a coral reef are altered. This can damage the coral reef because they are so sensitive to their surroundings and any changes it experiences. Increased turbidity, as a result of cyclonic winds, causes more sediment particles and material to be dispersed within coral reefs. This material can negatively affect the growth of coral and even kill it. Further more, the presence of more sediment within the water decreases the permeability of light to coral, which is necessary for photosynthetic processes. Mud sedimentation also decreases shelter availability for other organisms residing in coral reefs. Salinity levels decrease in ocean water due to increased waterfall. Corals will bleach from the resulting stress on water pH. Finally, sea levels will also decrease with the low pressure generated by cyclones. This leaves corals, that are usually submerged at specific sea levels, exposed. When sea levels are too high, light will not be able to reach the coral, which is essential for the coral to absorb nutrients and energy.
• Erosion: Increased amounts of broken coral, sediments, and other organisms are displaced due to stronger waver currents, which results in some areas of the reef being buried in sediment while others are left bare. At the same time, storm surges will uplift these materials and push them up to shore into features known as storm ridges. Storm ridges are usually the result of severe tropical cyclones. These are detrimental to atoll reefs because storm ridges have the potential to block off lagoons and induce deterioration of water quality. The breakage of coral reef depends on the location, shape and strength of the coral itself. Stronger storm surges are needed to break off pieces of larger colonies. Branching corals are recorded as being most affected, compared to colonies such as brain or boulder coral. This is because these massive colonies are more stable and create the foundational layer of coral reefs. The strength of coral can be further weakened by parasitic organisms and disease.

• biodiversity: Cyclones will have a profound effect on species richness, distribution and behavior.

Recovery

• time needed to return to original state
• greater damage can take anywhere between 5 to 40 years to recover

Impacts on the Great Barrier Reef

== Case study: Cyclone Ingrid ==

Tropical Cyclone Ingrid hit the Great Barrier Reef in March of 2005. Ingrid ranged between a category 3 and category 5 cyclone with winds up to 250 km/s; however, the actual size of the cyclone was small. The core of the cyclone was only 10-15 km diameter. The winds caused waves of up to 15 m in the open ocean and around 5 m in the Great Barrier Reef. The extent of the damage was caused by the fact that Ingrid hit three different states in Australia. This is the first time in history that a tropical cyclone hit this many states in Australia. The intensity of the damage was caused by the high winds in such a small area. The offshore reef had the deepest depth of damage, but the inshore reefs had the most coral reef and dislodgement. In the worst affected areas, the coral cover decreased 8x. The biodiversity decreased 2.5x and coral reefs decreased by about 30%.

Case study: Cyclone Yasi

Tropical Cyclone Yasi made landfall in Queensland, Australia in February of 2011. Yasi reached a category 5 cyclone with strong, damaging winds of 205 km/s.

How to Protect against Tropical Cyclones

• Marine protected areas
  • NTAs provide protection and act as sources of recovery after natural disasters

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