2.3 The Dynamics of Weather and Climate
The weather and climate play a key role in coral formation and in natural stress. Weather and climate dynamics include temperature, precipitation, winds and tropical cyclones
Temperature
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The ideal temperature for coral is between 20-27 degrees Celsius.
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If the water temperature is too low the zooxanthallae cannot produce the limestone. If the water temperture is too warm the zooxanthallae will leave the coral polyp and cause a bleaching event
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Thus, the location of coral reefs is of importance. Coral reefs are found in the low latitudes (flat lines are the lat lines) or more specifically in the tropics (Equator to 22 ½ degrees north and south of the Equator as the temperature in these areas is ideal for optimal coral growth
Precipitation
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Being located in the tropics the Great Barrier Reef experiences extensive tropical rain. Precipitation affects the Great Barrier Reef in two ways:
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One condition for OPTIMAL CORAL GROWTH is that coral needs water high in salinity. Precipitation is fresh water and with the heavy rainfall associated with tropical rain can cause Fresh Water Ponding. Salt water is denser (heavier) than fresh water. So, the fresh water pools on top of coral. This fresh water can kill coral exposed during low tide.
- Heavy tropical rainfall can cause flooding in rivers and wash down sediments and nutrients out to sea. Coral needs clear water free from chemicals and low turbidity to grow (see Clear Water)
Wind
- Wind has been responsible for shaping individual reefs through aeolion (wind) erosion
- Also wind has an influence on wave formation and currents.
- The South Easterly Trade Winds and periodic summer cyclones mainly affect The Great Barrier Reef.
Tropical Cyclones
- Tropical cyclones are intense low-pressure systems.They affect some parts of the Great Barrier Reef about once every six years. Their influence depends on their intensity and location. Cyclones can destroy parts of the reef and move huge blocks of coral (bommies) onto reef flats.
- The rain associated with cyclones also can decrease salinity (salt levels) of the water especially near shore lines and river mouths which can cause parts of the Great Barrier Reef coral ecosystem to die.