Genes of the Seven Wonders of the World: The Great Barrier Reef
The East Coast of Queensland is home to one of the Seven Wonders of
the World – The Great Barrier Reef (GBR). It’s the world’s largest coral reef,
covering more than 3000 000 square kilometers of sea. It is the only living
ecosystem that can be seen from outer space and is home to many marine animals.
It is made up of approximately 3000 coral reefs.

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Figure 1 |
Figure 1 represents three different phases of coral. Healthy coral
is surrounded by the symbionts, zooxanthellae and polyps, which are
microorganisms beneficial to the coral. They protect the coral skeleton and
help it to produce food and 90% of the energy required for growth and
reproduction. In return, the coral host provides these microorganisms with
protection and a continuous supply carbon dioxide through respiration, which is
important for photosynthesis.
When a coral has experienced a bleaching event it looses
zooxanthellae. Two things can happen
depending on the fitness level of the coral. It can reestablish its
zooxanthellae effectively recovering and physically increasing its tolerance to
heat stress. However, the coral experiences a reduction in growth and
reproductive rate and also becomes much more susceptible to diseases. As a result, we will see a reduction in the
population of these species of coral. Although the individual obtains increased
tolerance to bleaching events, at a molecular level, the DNA of the coral
remains the same and there is no benefit to any of the offspring as it is a
phenotypic change and not a genetic change. The other thing that can happen is
the coral will die and become covered in algae, which isn’t all that useful for
marine life.
In the last 20 years, there has been a 50.7% reduction of overall
coral population caused by bleaching among the GBR. Scientists are trying to
develop an understanding of coral genetics by viewing the genetic diversity of
the population. In order for a species to survive and adapt selectively, there
needs to be a broad range of genotypes to “select” from. So in event B, we can
see natural selection in play. There’s an increased surface temperature of the
sea, and one type of coral has a particular genotype, which has allowed it to
survive under this stress. And when it reproduces, the population shows an
increased abundance of fitter genotypes that are passed through the generations.
Unfortunately there is a shortness of genetic diversity in the coral population
and the ability for coral to adapt in an evolutionary sense is slow. It is
believed that some species of coral have a genotype that has a higher tolerance
level to climate change and decreased pH levels of the sea. Scientists are
currently trying to sequence the genome and determine a way to help coral
express this gene and increase their survival, however costs of this study is
demanding and quite challenging for scientists to understand.
By Britney Lergessner
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