Connor Scagnelli
10/27/2012
The Anthropogenic Coral Reef Destruction
The planet can be divided into several different biomes, which are characterized by
different ecosystems and climate. The largest biome found on our planet is the marine biome,
which is composed of oceans, coral reefs, and estuaries. Coral reefs are underwater
assemblages of calcium carbonate that make up one of the most biologically diverse
ecosystems (Hoegh-Gouldberg et al. 2007), supporting thousands of different species of
organisms. Coral reefs are made up of colonies of polyps, members of the phylum Cnidaria,
which attach to each other and excrete calcium carbonate which becomes the skeleton of coral
reefs. Recently, with increase in mean surface ocean temperatures, there has been an increase
in the loss of coral reefs due to bleaching and ocean acidification, and this will continue to be
the case as the oceans increase in temperature and absorb carbon dioxide from the
atmosphere (Hughes et al. 2003). Ocean warming and acidification is the direct result of the
increase in carbon dioxide in the atmosphere (Jacobson, 2005). The recent warming of the
climate, thought to be due to the release of anthropogenic carbon dioxide, has also been
increasing carbon dioxide levels in the ocean. The effects of this increase can be seen in coral
bleaching and slowing rates of calcification. If this trend of warming ocean temperatures
continues, it is predicted we will continue to lose coral reefs and the species of organisms living
in their ecosystems them until international policies are implemented to prevent reef
destruction or prevent further warming.
Coral reefs are one of the most important types of ecosystems not only because they
support so many different organisms, but because of the impact they have on the area of the
ocean they are found in and also on the resources they provide to Humans. Coral reefs greatly
influence food chains found in and around them, and these food chains are very susceptible to
perturbations, where slight losses in diversity lower in the food chain can have drastic effects
higher up (Nystrom et al. 2000). Reduction in the biodiversity of ecosystems also reduces its
health and ability to remain in a stable equilibrium (McCann 2000). These effects often can
detrimentally impact the fish higher up the food chain that are used as important food sources
by people living along the coast. Also with the loss of coral reefs, populated coastline-cities and
even countries that rely on tourism to support and stimulate their economy could face serious
economic problems.
Figure 1. The chart
depicts the breakdown
of component values
that contribute to the
global annual value of
coral ecosystems.
Coral reefs generate billions of dollars per year for the
As seen in figure 1, coral reefs generate billions of dollars per year, and the social, cultural, and
economic impacts that we would experience as a result from the loss of coral reefs would
extremely harmful and costly.
The two processes that are threatening the livelihood of coral reefs are bleaching and
acidification, which are both the result of increasing ocean carbon dioxide levels and ocean
temperature. Bleaching is a process where at high temperatures corals expel their
endosymbionts, called zooxanthellae, and lose their color (Hughes et al. 2003). Zooxanthellae
are photosynthetic algae that are responsible for the bright colors of color reefs. The products
of photosynthesis are used by the coral they live in, and in return coral provides inorganic
nutrients which the zooxanthellae recycle. This symbiotic relationship results in the ability of
corals to sustain a high biodiversity. The photosynthetic ability of zooxanthellae makes it
possible for many other organisms to live on the coral, and to promote a high biomass. The
food chains in coral reef ecosystems are supported by this relationship, and without it, there
would be a great reduction in the diversity of organisms found living on and around reefs.
When levels of zooxanthellae become too high, they are expelled by the coral, and this is a
regularly occurring and natural process. When a coral is stressed however, such as it is at high
ocean temperatures, up to 60-90% of the symbionts are expelled. If corals are not able to retain
the zooxanthellae lost during the disturbance, they will eventually die.
Figure 2. This
graph shows
how the
average surface
temperature of
the world's
oceans has
changed since
1880. This
graph uses the
1971 to 2000
average as a
baseline for
depicting
change.
As seen in this graph, over the past three decades, average ocean sea surface temperatures
have increased at unprecedented rates of .21 degrees per decade. It is predicted that because
all coral respond in such a way to thermal stresses, and because coral are not able to readily
adapt to the foreseen increase in ocean temperature, all coral reefs will soon be threatened by
bleaching (Hughes et al. 2003).
Ocean acidification is when carbon dioxide, absorbed from the atmosphere, results in
higher levels of the hydronium ion and a lower pH in the ocean. The ocean has a complex buffer
system to maintain a somewhat constant and predictable pH. Carbonic acid and bicarbonate
respond to changes in pH and make up this buffer system. When carbon dioxide is dissolved in
water it forms carbonic acid. At high levels of carbon dioxide in the ocean, carbonic acid
dissociates into bicarbonate and hydronium at greater rates, resulting in a decrease in pH. At
lower pH’s, when hydrogen ions are more abundant, they react with carbonate to form
bicarbonate. Carbonate is the compound used to build the skeletons of coral reefs, and such an
increase in hydrogen ions in the ocean leads to coral reef deterioration and destruction (HoeghGouldberg et al. 2007). Such acidification not only corrodes living coral reefs, but it also
prevents the growth and recovery of already weakened reefs by slowing down calcification
rates. This then has indirect effect of making corals more susceptible to predators such as
starfish. Overall acidification is an extremely harmful process and increases of ocean aciditiy in
the past decades can be attributed to the increase of carbon dioxide in the atmosphere
(Jacobson, 2005).
One of the most significantly impacted coral reef ecosystems has been those located in
the Caribbean Sea, where climate change and local factors such as over fishing and predation
have resulted in extreme loss of coral coverage (Gardener et al. 2003). These patterns of coral
loss have been observed locally and sub-regionally, but coincide with trends on a region wide
scale. As seen I figure 3, there has been a distinct loss in percent coral coverage from about
50% to 10% just in the last three to four decades. This devastating loss cannot be fully
attributed to the recent increase in atmospheric temperature and CO2 levels that has also
occurred in the past three decades. However, these areas have experienced coral bleaching and
acidification; the telltale signs that ocean temperature and acidity are becoming problems. This
study also found that areas in the Caribbean that were previously inhabited and dominated by
coral have been replaced with algae that tend to thrive in warmer temperatures. There has also
been a shift in coral species, where opportunistic coral species have recently increased in
frequency. These new species who are taking advantage of the recent mortality of other,
previously dominant coral species are thought to be more susceptible to thermal stresses and
storm damage. With the extreme loss of coral coverage and change in community composition
in the Caribbean, the future of these reefs does not bode well as global climate change and
increased rates of ocean temperature will potentially increase the rate of loss of coral coverage.
Figure 3.
Total observed change in percent coral cover across the Caribbean basin during
the past three decades. (A) Absolute percent coral cover from 1977 to 2001.
Annual coral cover estimates (▴) are weighted means with 95% bootstrap
confidence intervals. Also shown are unweighted mean coral cover estimates for
each year (•), the unweighted mean coral cover with the Florida Keys Coral
Monitoring Project (1996–2001) omitted (×), and the sample size (number of
studies) for each year (○).
There have always been ocean temperature fluctuations that many coral reefs have
been able to adapt to, but the question now is if coral will be able to adapt at fast enough rates
to keep up with the effects of climate change. It is unknown whether the increase in ocean
temperatures will cause a complete die off of corals in specific areas in the world or cause
corals reefs to have to move away from the equator, towards the poles, but there has been one
finding that suggests certain coral reef systems might be able to resist these thermal stresses.
In a study by Todd C. LaJeunesse et al. in 2010, it was found that zooxanthellae, specifically
the clade D type, were frequently resistant to coral bleaching. This type of zooxanthellae is
found primarily in the northeastern part of the Indian Ocean, where average temperatures are
often higher than other parts of the Indian Ocean. These other areas, where the clade D type of
zooxanthellae is not found, have experienced extensive bleaching. This is promising and
reassuring news that corals and their endosymbionts have been able to adapt in the past to
changes in ocean temperature, and may be able to adapt in the future. In areas where species
of coral cannot adapt, the clade D zooxanthellae could be introduced; however the
effectiveness consequences of introducing a new species of zooxanthellae still need to be
researched.
The current destruction of coral reefs and the foreboding future that awaits them can
be attributed to anthropogenic climate change. Recent increases in anthropogenic carbon
dioxide levels in the atmosphere over the past hundred years or so have led to increase
atmospheric temperatures, as a result of the greenhouse effect. The ocean is able to absorb
both heat and carbon dioxide form the atmosphere. As the atmosphere has increased in carbon
dioxide and temperature, so has the ocean (Jacobson, 2005). It is believed that the increase of
carbon dioxide levels is due to the increase in industrial production that has occurred over the
past century. The most effective way to reduce potential coral reef destruction would be to
reduce carbon dioxide emissions. This would most likely have to be a long term plan, and would
require complete international alliance and teamwork. There may not be any way to save the
coral reefs that are currently under dire threat, however reef management techniques that
prevent human destruction or over exploitation could be implemented to help foster recovery.
It is hard to predict what lies ahead, even with extensive use of climate models, it is uncertain
what will happen to the vital coral reef ecosystems. As of now, things couldn’t look more
formidable, with increases in coral bleaching globally. All that can be done for now is to
increase research on coral reef protection and management, and to find ways to reduce the
carbon dioxide that is currently being released into the atmosphere.
References:

Gardner TA, Cote IM, Gill JA, Grant A, Watkinson AR. 2003 Long-term region-wide
declines in Caribbean corals. Science 301, 958 – 960. (doi:10.1126/science.1086050)

Hoegh-Guldberg, O. et al. 2003.Coral Reefs Under Rapid Climate Change and Ocean
Acidification, Science 14 December 2007: 1737-1742. [DOI:10.1126/science.1152509]

Hughes, T.P. et al. 2003. Climate Change, Human Impacts, and the Resilience of Coral
Reefs,
Science 15 August 2003: 929-933. [DOI:10.1126/science.1085046]

Jacobson, M. Z. (2005). Studying ocean acidification with conservative, stable numerical
schemes for nonequilibrium air-ocean exchange and ocean equilibrium
chemistry. Journal of Geophysical Research – Atmospheres 110:
D07302. Bibcode 2005JGRD..11007302J.doi:10.1029/2004JD005220.

LaJeunesse, T. C., Pettay, D. T., Sampayo, E. M., Phongsuwan, N., Brown, B., Obura, D.
O., Hoegh-Guldberg, O. and Fitt, W. K. (2010), Long-standing environmental conditions,
geographic isolation and host–symbiont specificity influence the relative ecological
dominance and genetic diversification of coral endosymbionts in the
genus Symbiodinium. Journal of Biogeography, 37: 785–800. doi: 10.1111/j.13652699.2010.02273.x

McCann, K. S., 2005. The diversity-stability debate. Nature 405, 228–233.

Nyström, M. et al. 2000. Coralreef disturbance and resilience in a human-dominated
environment, Trends in Ecology & Evolution, Volume 15, Issue 10, 1 October 2000,
Pages 413–417
Image Bibliography

Absolute Percent Coral Cover from 1977 to 2001. Digital image.Sciencemag.org. Science, 2003.
Web. <http://www.sciencemag.org/content/301/5635/958.full>. (figure 3)

Average Global Sea Surface Temperature, 1880-2009. Digital image. EPA.gov. NOAA, 2010. Web.
<http://www.epa.gov/climatechange/science/indicators/oceans/sea-surface-temp.html>.
(figure 2)

Economic Value of Reefs. Digital image. National Oceanic and Atmospheric Administration. N.p.,
14 Dec. 2012. Web. <http://coralreef.noaa.gov/aboutcorals/values/>. (figure 1)