Faculty Editor: Professor Jeffrey DaCosta

Coral reefs are complex, diverse, and productive structures that have played a crucial role in tropical ocean ecosystems over the past 200 million years.2  Their importance is  attributed to providing a primary form of protection for organisms vulnerable to predation and facilitating a high level of production in waters with very low levels of the nutrients necessary for effective primary production.2  Corals and associated organisms play a key role in a very complex food chain that provides for the most diverse marine ecosystem on the planet.2  Not only do they serve an important role for shallow water inhabitants, but also for humans by playing key roles within the fishing, tourism, coastal protection, building materials, and drug discovery industries.2  Unfortunately, the overall health of coral reefs worldwide is in rapid decline due to both human activities and natural phenomena.  It is important to raise awareness regarding the domino effect that the destruction of coral reefs would trigger so that we can facilitate new growth and prevent further destruction.

Coral reefs are composed of three different types of organisms— the reef building corals that make up the framework, the algae that welds the structure together and hundreds of thousands of organisms that populate reef systems, including fish, birds, marine reptiles, mammals, invertebrates, and bacteria.2  The dinoflagellate zooxanthellae inhibit the tissues of coral and live symbiotically within their host’s cells.  The photosynthetic activity of zooxanthellae is the chief source of energy for the process of calcification, which is both energetically expensive and necessary for coral and its survival.2  Zooxanthellae normally show low rates of migration or expulsion, but have been observed to undergo inconsistent seasonal changes that are believed to depend on physical changes in their immediate environment.2  Factors including reduced salinity, changes in light or temperature, the presence of chemical compounds, and the presence of particular bacteria can cause corals to lose their pigmentation.2  In most cases, this color change is due to the physical loss of zooxanthellae or the loss of their pigmentation.  Since the loss in pigmentation causes the coral to become white in color, this phenomenon is known as coral bleaching, and is associated with high levels of coral mortality.  In fact, entire reef systems have been found to lose almost all of their reef-building corals following bleaching events.2  When this is the case, it becomes what is known as a mass bleaching event.  More severe mass bleaching events are almost always associated with elevated sea temperatures.2

It is believed that the average tropical ocean temperature has varied by less than 2 °C over the past 18,000 years.2  However, many of these waters have warmed by almost 1 °C over the past 100 years, and are currently warming at as much as 1-2 °C per century.2  In response to such drastic changes, organisms have three options.  The first is acclimatize through physiological modification of their cellular respiration process.  Secondly, the natural selection of individuals who are better suited for the environmental changes at hand are more likely to survive and reproduce for longer, leading to a greater number of offspring equipped with genes that make them better able to survive, as well.  Acclimatization in regards to temperature changes can occur on the order of just hours or days, while adaptation through natural selection often requires hundreds or even thousands of years before it is successfully in changing the gene pool, especially in individuals like corals that have longer generation times.2  Their third and final option is extinction.

Recent thermal events have been too short and sporadic to allow corals and zooxanthellae to acclimate or adapt quickly enough to promote their healthy survival.2  It is predicted that thermal tolerances of reef-building corals will be exceeded every year for at least the next few decades.2  It has also been observed that coral mortality is correlated with the magnitude and the longevity of sea temperature increase.2  On top of this, increased sea temperatures also have indirect negative effects on coral communities— decreased alkalinity and rise in sea level.2  Most biological organisms can only function optimally within a narrow range of pH values, and the increased concentration of acidic ions associated with warmer waters can have a drastic impact on coral communities.  As for rising sea levels, it is estimated that sea level has risen by as much as 25 centimeters over the past 100 years, and a sea level rise of 95 centimeters is predicted to occur over the next century.2  This would prevent more of the light essential for coral-building from reaching coral communities.

A research study was conducted to determine the effects of declining health in coral reefs, and the results were very discouraging.  Species diversity and number of individuals within reef systems were measured on reefs that were healthy, dead, and reduced to reef rubble, which consists of dead, unstable pieces of coral.  Species diversity was for the most part maintained in all dead reefs when compared to living ones, however the species diversity of the rubble reef was significantly reduced in comparison.5  It was also found that the decrease in living space, protection, and food associated with both dead and rubble reefs led to complete disappearance of coral-polyp feeders, a decrease in resident species and individuals, and even a decrease in the numbers of species and individuals that visited.5  These findings indicate that any decrease in coral health can cause changes to not only the ecosystem of the coral reef itself, but also surrounding ecosystems.  The long-term effects of such a decline could be astronomical.

Since the reduced health of reefs is associated with the decline in fish population of shallow coastal waters, this pattern has a large effect on the fishing industries of nearby communities.  For example, in the Philippines, over one million small-scale fishers earn their living from coral reef fisheries, and this group contributes 1 billion USD annually to the country’s economy.6  Reef fish can contribute up to 20% of the total fisheries of the Philippines each year, and in some of the smaller Philippine islands, this number can be as high as 70%.6  As much as 50% of the animal protein consumed in the Philippines is derived from marine fisheries and aquaculture.6  Not only are the fish from coral reefs used for consumption, but this region also has a large export industry for live fish, which are often sold for use in aquariums and similar cultural establishments.  The heavy reliance on reef fishing for the physical and economic well-being of the Philippines is just one example of how human life is already being negatively impacted as a result of the destruction of our world’s reef systems.

Not only does coral destruction negatively affect quality of reef fishing, but the act of reef fishing itself involves many practices that can negatively impact the reefs in return.  Fishing in general causes destruction to coral reefs due to damage from ships’ anchors. Boats used for fishing generally drift along with the anchor thrown overboard until it becomes hooked on a piece of coral to immobilize the boat.  Unfortunately, the anchor usually breaks off several pieces of coral before it finally becomes hooked on one, and often dislodges at least one more while being retrieved.3  Due to waves and water currents, there is little to no chance of these broken-off pieces being able to assimilate back into the reef at any time.3

As the global population grows, especially in coastal developing communities, there is a greater demand for food and a greater number of competitors within the fishing industry.  One result of this growth is the danger of overfishing, meaning that species are being removed from the region at a rate that does not allow natural repopulation. It has been hypothesized that fish catches have already shot above healthy levels in many reefs.6  Additional impacts of a growing population include the development and use of more destructive and cost effective fishing methods, so that as many fish may be killed for as little capital as possible.  Two of the most popular of these techniques are poisoning by sodium cyanide, and blast fishing. Both of these practices were banned in several countries as early as 1979, but are still used extensively to this day.3  The use of sodium cyanide and similar poisons has been estimated to cause mortality in as much as 8% of corals per year, and blast fishing is even more destructive.3  Blast fishing is the use of dynamite or other explosives in order to quickly kill or stun large schools of fish for easy collection.  Unfortunately, this technique does not have the ability to selectively kill only the species fishers are hunting for. Any organisms, including corals, that may be in the vicinity will also be affected by the explosions.  Not only is this extremely reckless and destructive, it also becomes less cost-effective as it is practiced more and more, since species and organism densities decline with coral destruction. This means that less and less fish are being captured by each explosion as time goes on, prompting fishers to just use more explosives.  This practice has been known to reduce the growth capacity of certain coral populations by as much as one third, and could result in a net loss of coral cover of 14% per year.3  Several of the practices currently being used for reef fishing are part of dangerous and disastrous negative feedback loops that are contributing to a grim outlook for coral reefs. 

Not only do coral reefs act as a safe haven for possible prey hiding within their polyps, but they can also serve as protective devices for terrestrial organisms in nearby coastal regions, including humans.  In areas that are prone to large waves or storms, including ones as severe as hurricanes or tsunamis, reefs can provide a barrier against storm damage, erosion, and coastal flooding.2  It is even possible for the human eye to see a deflection and decrease in speed of tsunami waves as they encounter reefs while approaching the shore.1  However, with destruction of these coral reefs, low-resistance paths are created that permit water jetting into the land, causing increased damage.1  Implications for human well-being include increased property and structural damage, along with increased loss of human life in regions where reefs have experienced blast fishing.1  In the Philippines alone, there could be as much of a $25,000 USD benefit from the prevention of such erosion and physical damage to the landscape.6

Another way in which reefs contribute to the economy of coastal nations is through tourism.  Even in their degraded condition, reefs in the Philippines contribute over 1.3 billion USD annually to the economy.6  This money comes from fees for scuba diving, snorkeling excursions, and resorts, among other tourist and recreational activities.  Not only that, but visitors of the reefs are often willing to contribute monetarily in order to aid in reef management, which is a huge positive that comes out of the tourism industry.6  However, the business of tourism is not without some harmful effects to reefs, as boats carrying tourists often damage the coral with their anchors in the same ways that fishing boats do.6

These are only the major factors that are currently causing extensive damage to our planet’s reef systems.  Even the very habitat that allows corals to be so productive can cause damage through physical erosion from wave action.5  Infestations of species that feed on corals, such as the starfish Acanthaster planci in the Indo West Pacific, can infest reefs, and cause extensive declines in coral populations.5  Corals are stenohaline osmoconformers, meaning that they can only tolerate and survive small changes in salinity.  Consequently, rapid decreases in salinity following severe rain storms or flooding events can cause mass mortalities of corals, as well.2  Finally, increased sedimentation in reef areas, whether natural from river deltas, or unnatural from water pollution, can make waters surrounding and above coral structures murky, and prevent the sunlight they need from reaching them.2 

The applications of coral reefs are endless, even without taking into account other aspects of the highly productive ecosystem they cultivate.  Corals boast significant usage in building materials, decorations, jewelry, food, collections, crafts, antibiotics, and other medicinal drugs, just to name a few.  Thankfully, there have already been many efforts initiated worldwide in order to prevent further destruction. The first step in making a change is raising awareness regarding the issues at hand.  Unfortunately, even in places where fishers are becoming more cognizant of the impacts of their actions, their destructive fishing behaviors have yet to change. Increasing awareness about the personal and environmental risks of such behaviors and the laws prohibiting them have not been enough to make an impact, likely due to the expenses and ineffective implementation of such laws.4  The total cost of complete loss of coral reefs can be expected to be hundreds of billions of dollars every year, and the costs of preserving these gorgeous structures pales in comparison to that figure.2  It’s likely that if government officials were more aware of these statistics, they would allocate a greater budget towards reef preservation and increased enforcement of fishing regulations.  On top of that, local fishers will require alternative ways to make their livelihoods, so local governments need to support the development of reef-related industries that are both profitable and healthy for corals, such as more sustainable fisheries, mariculture, and tourism.4  It is important for citizens and governments to collaborate in order to ensure the success and longevity of such a transition.Many fishers have commented that while reefs near their homes have been destroyed, there are plenty of undamaged reefs further from the shore.4  This is a common, yet ecocentric and quite honestly misguided mindset when it comes to many of the environmental issues our planet is currently facing.  Hopefully, for the sake of the Earth and the human race, we realize the extent of our interconnectedness and that as creatures of this planet it is our responsibility and duty to protect the beauty and diversity of our home.


  1. Fernando, H. J., Mcculley, J. L., Mendis, S. G., & Perera, K. (2005). Coral poaching worsens tsunami destruction in Sri Lanka. Eos, Transactions American Geophysical Union, 86(33), 301. doi:10.1029/2005eo330002
  2. Hoegh-Guldberg, O. (1999). Climate change, coral bleaching and the future of the world’s coral reefs. Marine and Freshwater Research, 50(8), 839-866. doi:10.1071/MF99078
  3. McManus, J. W., Reyes, R. B., Jr., & Nañola, C. N., Jr. (1997). Effects of Some Destructive Fishing Methods on Coral Cover and Potential Rates of Recovery. Environmental Management, 21(1), 69-78. doi:10.1007/s002679900006
  4. Pet-Soede, C., Cesar, H., & Pet, J. (1999). An economic analysis of blast fishing on Indonesian coral reefs. Environmental Conservation, 26(2), 83-93. doi:10.1017/s0376892999000132
  5. Sano, M., Himizu, M., & Nose, U. (1987). Long-term effects of destruction of hermatypic corals by Acanthaster planci infestation on reef fish communities at Iriomote Island, Japan. Deep Sea Research Part B. Oceanographic Literature Review, 34(12), 1067. doi:10.1016/0198-0254(87)96068-7
  6. White, A. T., Vogt, H. P., & Arin, T. (2000). Philippine Coral Reefs Under Threat: The Economic Losses Caused by Reef Destruction. Marine Pollution Bulletin, 40(7), 598-605. doi:10.1016/s0025-326x(00)00022-9

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