Hurricanes are forces of nature that cause destruction wherever they go. In an earlier post, the effect of
hurricanes on land were discussed, but now we focus on the actually point of this blog, their effects on coral
reefs.
When a hurricane approaches land the force of the wind and sea push water unto to the land in what is
known as a “storm surge”. This water can erode the land near the sea and change the mineral content of the soil. The effects of storm surges on land can be reduced by coral reefs [1]. The coral act as a
surf break, where the force of the waves is dissipated when the water has to flow against/around the structures. This reduces the energy the wave possesses so that the height and inland intrusion would be reduced.
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| Image Credit: The Pew Charitable Trusts |
According to the article “ Hurricanes and their effect on coral reefs” by the Global Coral Reef Monitoring
Network, the force of the waves can often be too strong for the corals to withstand so branches and whole
coral colonies are broken or uprooted from the reef. This can further add to the destruction when these loose pieces are picked up by the wave and thrown against the reef. In the Caribbean, mainly branching elkhorn (Acropora palmata) and staghorn (Acropora cervicornis) coral are broken by intense wave action. Whole tubular colonies are often broken at the base, where it then acts like a wrecking ball on the other coral. [2]
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| Photo Credit: ESI |
The article further went on to say that, the rolling motion of the wave also picks up sand and other debris
from the ocean floor, carrying it with the waves. The heavier particles containing sand and nutrients, would
settle on corals causing algae growth [3]. This can be further aided by agricultural runoff, where nutrients from fertilizers are washed into the sea enriching the water with minerals needed to help the algae grow. The algae rapidly grows over the coral surface smothering it, blocking nutrients, oxygen and light, eventually killing the coral [4]. The lighter particles can remain suspended turning the water opaque. This can prevent light from reaching the remaining coral, stopping zooxanthellae (organisms that share a mutualistic symbiotic relationship with the polyps) from photosynthesising. This reduces the amount of oxygen the coral receives, which suffocates it.[5]
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| Photo Credit: Reef Assessment Monitoring Program |
Hurricanes also bring large amounts of rainfall. This addition of fresh water to the environment may be good for land plants but it has devastating effects on marine life. The large quantity of fresh water added to the sea changes the salinity of the water [6]. This reduction of salt content causes the osmotic pressure in corals to change. More fresh water is taken in creating stress on the corals. [7]
This stress in turn can causes mass coral bleaching. The mechanical damage and chemical composition of the water affects the coral so much they release all their zooxanthellae (microorganisms that give corals their characteristic colour) turning them white. They do this in an effort to recover but if the damage is to severe the zooxanthellae will not be accepted back and the polyp will eventually died. [8]
References:
[5]HURRICANES, BACKGROUND TO, “3. Hurricanes and their effects on coral reefs.” Status of
Caribbean coral reefs after bleaching and hurricanes in 2005 31 (2008)
[6]Jackson, J. B. C., M. K. Donovan, K. L. Cramer, and V. V. Lam. “Status and trends of Caribbean coral
reefs.” Gland: Global Coral Reef Monitoring Network, IUCN.
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