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05. HUMAN IMPACT ON THE REEF

5(c) Sunscreen for Corals

Some corals have adaptations to survive coral bleaching. That is, they have their own natural protection. They produce a kind of sunblock, called a fluorescent pigment. These pigments form a shield around the zooxanthellae and at high temperatures they protect them from the harmful effects of sunlight and UV rays. They change the harmful UV and blue wavelengths in sunlight, to lower energy wavelengths like green and yellow. Therefore, fluorescent corals tend to survive bleaching events better than non-fluorescent ones. Some corals are obviously hardier than others and have a better chance of survival. Over time, fluorescent corals may be favoured over ones that don’t have these fluorescent pigments, so evolutionary changes may occur in our coral species.

The diversity of species we have today is a product of evolutionary adaptation. Species acquire their unique characteristics through genetic changes, biological adaptation and natural selection. Adaptations may include aspects of structure, physiology or behaviour that increase the organism’s chance of survival and reproductive success. Put simply, the process of evolutionary adaptation involves the following:

  • Genetic differences exist between members of the same species.
  • Those individuals with naturally occurring characteristics, that are favourable in a changed environment, will survive. (Charles Darwin’s principle of the ‘survival of the fittest’.)
  • When they reproduce, they pass on these adaptive characteristics to their offspring.
  • As a whole, the species then becomes better adapted to its environment.

If the environment changes too rapidly, there are two possibilities:

  • Some species may not possess the necessary characteristics to allow them to survive in the changed environment. If a species does not possess this diversity, then it will become extinct.
  • Species that possess a high genetic diversity have ‘contingency plans’ whereby certain populations have characteristics that enable them to survive in the changed habitat, at the expense of others.

Organisms like bacteria, with high reproductive rates and short generations, tend to have higher rates of mutation than longer-lived species, like elephants. Therefore, bacteria are able to evolve more quickly. This is why disease-causing micro-organisms are able to keep ahead of the drugs scientists have to combat them.

The more that genetically narrow, homogeneous genotypes are promoted, the more vulnerable these species become to environmental changes. Life on Earth depends on maximal genetic diversity.


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