For centuries, coral reefs have been recognized as one of the most diverse ecosystems on the planet. Commonly known as “the rainforests of the sea”, they are home to a wide variety of marine life and, consequently, they are frequent tourist attractions around the world (Sanctuary, Florida Keys National Marine). With coral reefs “covering less than one percent of the Earth’s surface and less than two percent of the ocean floors”, the amount of resources provided to the worlds’ species is unprecedented (Frost, Emily). Recent studies, however, have found that due to the continuous stress from internal and external factors, these admired ecosystems are deteriorating. Environmental factors combined with negative human involvement, are to blame for the constant elimination of reef life on Earth. Coral reefs, not only stand as an ecosystem for an abundant amount of organisms, but also provide a food source and source of protection to many (Shah, Anup). Aside from these, the ecological and economical benefits are also a direct result when these reefs flourish. Everyday, nonetheless, different stressors are causing immediate and even long lasting damage to reef life, which in turn, is presently causing and prospectively can cause negative effects for other life on Earth, as well. Brian Walker described the modern day situation accurately when he stated "Understanding how these resilient corals respond to present environmental conditions informs us of how the environment has changed. The fact that they are dying now after living hundreds of years, may indicate that their surroundings are much more stressful than ever before" in David Fleshers article, “Corals off South Florida hit with severe Bleaching”

Based on individuals’ views on the severity of reef damage, many will argue that reef life is a fluctuating system that is constantly changing from high productivity to low productivity, so there is no need to worry about the preservation of these habitats. Claims such as “the Great Barrier Reef has died” are rejected by many and are refuted by saying those articles are “over-exaggerated” and “false news” (Milman, Oliver). Although there is a high amount of genetic diversity and there is fluctuating productivity levels, it is not guaranteed that these qualities will save reef life from extinction. Genetic diversity provides a large gene pool that ensures an ideal, steady and unceasing life on coral reefs (Milman, Oliver).  A larger gene pool allows for a species to continue even if subpopulations are wiped out due to natural disasters or negative human involvement. Individuals, with views similar to Oliver Milman, state that “these ecosystems are able to recover” from blows to certain populations and subpopulations in reef life. In Milman’s article, “The Great Barrier Reef is Under Severe Stress- But Not Dead Yet”, for example, he addresses the “fatalistic” appearance of the reef, but quickly points out the resilience of the reef, and how it will continue to live for years, especially if humans become proactive. In spite of that, however, the problem with this theory is that if the entire reef is affected from these factors, every population may face risks for the continuation of evolution and reproduction. 

Corals and Coral reefs are found all over the world’s oceans, stretching geographically from the coast of Alaska to the warmer waters of the Caribbean Sea (Frost, Emily). Some of the largest coral reefs are found in the clear, shallow waters, within the tropics and subtropics. In these locations, reefs grow the fastest and are among the most productive and diverse ecosystems on Earth (Lallanilla, Marc). The algae found within coral tissues are in need of this light for photosynthesis and prefer water temperatures between seventy and eight-five degrees Fahrenheit (Frost, Emily).  With over one quarter of the worlds’ oceanic species depending on coral reefs, the developed symbiotic relationships are extremely dependent on the survival of these ecosystems (Frost, Emily). Algae and coral, for example, are one of the many relationships that parallel with the health of specific reef set ups. Coral provides algae with “compounds used for photosynthesis”, as well as shelter, while algae provides a stable amount of oxygen, food and even removes coral wastes. With the slightest change in temperature, or increase in water pollution, a process called “coral bleaching”, often abbreviated as just “bleaching”, can be initiated (Worland, Justin).  Bleaching is a coral’s response to an unfamiliar change in its environment, often resulting in its natural death, and has even hit more than ninety-three percent of the Great Barrier Reefs (Slezak, Michael).  As its environment is altered, an immediate expulsion of the corals’ algae is completed leaving the coral, white, extremely vulnerable to diseases and with a lack of a sustainable food source (National Ocean Service Education). Coral reefs, by supporting more than four thousand species of fish and more than eight thousand species of “hard coral”, are habitats that sustain more species per unit area than any other salt water environment (NOAA). 

We can all agree that different contributing factors relating to coral and coral reef life are of serious concern within the past ten years, however, the recent spike in mortality rates are alarmingly high, and are in need of serious attention. Negative human involvement has been one of the most influential factors in contributing to rising mortality rates on coral reefs around the world, along with ecological factors.  In Justin Worland’s article “A Most Beautiful Death”, the report “predicts that twenty-four percent of the worlds reefs are under imminent risk of collapse through human pressures; and a further twenty-six percent are under a longer term threat of collapse”.  The different ways humans have negatively impacted coral reefs around the world include, but are not limited to: Overfishing, Coastal Development, climate change and pollution.

Overfishing and destructive fishing methods have “been identified as the most pervasive of all local threats to coral reefs” (Reef Resilience). The World Wildlife Fund defines overfishing as “when more fish are caught than the population can replace through natural reproduction”.  In some areas, such as Southeast Asia, up to ninety-five percent of their reefs have been affected by overfishing and unsustainable fishing methods.  Overfishing and impractical fishing methods can have severe affects on oceanic populations as it can disrupt the natural balance of oceanic relationships.  Because fish are one of the top selected food sources for humans, it pushes fisheries to decrease their safeguards towards fish populations in order to increase their own financial incomes.  Due to overfishing and destructive fishing methods, “commercial fish populations have declined to a point where survival as a species is threatened (Reef Resilience). As more fish population dwindle down, the natural predators of these fish begin to face scarce food supplies, having to spend more energy and time in order to find a food source. Most all populations that have a relationship, either directly or indirectly, are affected by a change in fish communities. 

Coral reefs are highly overfished and often are done so by using destructive fishing mechanisms, such as stunning and netting types. Many fisheries use explosives in a process called “dynamite fishing” or “blast fishing” to help stun different fish populations for easier catching. These “blastings” effect the coral and neighboring reef populations by killing off majority of the oceanic plant life. Blast fishing is used in shallow reef systems and will often times reduce the reef down to a state of near nonexistence. By destroying the majority of these habitats, the reef can die quickly and not be able to support much, if any, life. Another example of a destructive fishing mechanism, is the spraying of cyanide into a reef (Reef Resilience).  Cyanide fishing, although banned in most areas around the world, is still illegally practiced, largely throughout Southeast Asia (Scientific American). Cyanide is used to stun the targeted population of fish causing damage to reef life by its lethal effect on coral. Typically, whatever is left of the coral reef, that the cyanide did not kill off, the divers do.  Often times, divers that are using the cyanide, break off large portions of the coral when attempting to catch the fishes.  According to reef resilience, about one third to one half of the fish populations collected through this method die soon after harvesting, “making this a particularly destructive method of harvest”. The netting used by many fisheries is the final example of destructive fishing techniques. Nets such as gill nets have been thrown overboard by fishermen or have been deposited into different reef systems via storm or winds. Once a net floats away or is taken from the fishermen’s’ possession, the nets become known as “ghost nets”. Ghost nets are notorious for catching animals such as sea turtles, dolphins, and other reef life in its net, entangling them to a point where they can not get free.  Once entangled in these nets, animals slowly can starve, become an easy target for predators to attack, or even suffocate. All of these mechanisms have had a negative impact on reef life, and have significantly contributed to the spike in death rates (Scientific American).

Coastal Development is another way humans have negatively impacted coral reef ecosystems. According to Reef Resilience, about forty percent, or around 2.5 billion people, of the worlds population lives within 60 miles of a coast, which has “add[ed] increased pressure to coastal ecosystems”.  Construction is a huge factor in the harmful effects of coastal development. Majority of the land used for human’s coastal development has been reclaimed land from shallow reef flats and marine estuaries (Reef Resilience). Areas like this have been “converted to airports, industrial or urban areas” and are expanding each year. Construction from these sites have caused reef life to decrease as the adjacent reefs have sediment and chemicals poured into the surrounding areas. Soils and sands used to fill these areas have been known to wash back into surrounding reefs as well, causing turbidity and the reefs themselves to be smothered under heavy sediments. Dive reefs, such as the ones in Palm Beach in Florida, are an example of how these sediments effect such reefs. As temperatures have increased and sediments and run off have been added into the waters off of Florida’s coasts, the corals were hit with bleaching extremely hard, “in what experts call one of the worst episodes in two decades of coral bleaching” (Fleshler, David). Piers, man-made channels, airport landing strips and many more have been known as the top reasons for human expansion into areas of coral reefs (Reef Resilience). As these expansions are rising in number, the more reefs are directly impacted. Not only are coral being affected, but the species living in these ecosystems as well. Habitats are being run down and drained, leaving hundreds of different organisms without shelter or a source for food. Chemicals that are poured into the marine waters have even been known to change metabolic processes in different communities of salt water species. Chemicals such as hydrocarbons, industrial waste products, pesticides and pharmaceuticals are just a few examples of what humans have put into surrounding marine ecosystems. As these are added, the salt water environment becomes more stressed and species sensitivity rises. These pressures can lead to mortality and biologically impairing developments such as the photosynthetic depression caused by an increase in organochlorine pollution from exposure with DDT, in a study conducted by McCloskey and Chesher. (pp.189 Negri, Andrew). 

Another huge contributing human factor to a decline in reef life is the role humans have played in climate change. Coral reefs have been known to be extremely sensitive to changes in temperature, leaving them vulnerable to bleaching, starvation and diseases. Faced against erosion and other environmental factors, it is important that coral keep their health up to par and fight off possible bleaching from a rise in sea temperatures.  Human activities, such as burning fossil fuels, however, have negatively added to the natural greenhouse gases effect. The greenhouse gases and aerosols have majorly lead to increased global temperatures, significantly so within the past decade. By burning fossil fuels, large amounts of gases such as Carbon Dioxide, have been added into the atmosphere, “altering incoming solar radiation and outgoing infrared (thermal) radiation that are apart of Earth’s energy balance” (Australia Government Marine Park Authority). By burning majority coal, oil and gas, the emissions sent into the atmosphere have since prevented the Earth’s emitted infrared radiation from leaving the atmosphere, and is in turn warming the Earth. As this atmosphere warms, the sea temperatures do as well. This rise in temperature causes bleach sensitive coral such as the Staghorn Coral to “be the most seriously affected” (Australia Government Marine Park Authority). From this point, it becomes easier for “large fleshy seaweeds (macroalgae)” to compete for coral reef space, as they typically are unaffected by rising temperatures. This is damaging to a reef system as “reefs dominated by macroalgae and bleaching-resistant corals have less three-dimensional structure than healthy coral reefs. Such reefs provide fewer shelters and refuges for the many animals that rely on the reef for their habitat” (Australian Government Marine Park Authority). 

Finally, the most detrimental human impact brought to coral reefs is the skyrocketing amount of pollution. Along with the chemical and discharge of factories, industrial plants and sediment, comes humans waste. The two major sources of human pollution are land-based pollution and marine debris (NOAA). Sewage outflows from households along with petroleum products and plastics, from land dumps, are just a few of the pollutants added to coral reef and oceanic ecosystems. As these products are added into marine waters, it decreases the amount of oxygen present in the water along with having a decrease in water quality. As oxygen levels become lower, photosynthesis for algae and other marine flora become limited. This can also lead to increased macroalgae growth and “crowding out corals” on the reef areas and “significantly degrading the ecosystem” (NOAA). The added pollutant can also make it hard for the other reef organisms to breath and can interfere with species reproductive capabilities. By adding products such as these into the reef systems, the introduction of pathogens may also begin, causing abnormalities in individuals’ physical and genetic makeups.  Marine debris is defined as “any human-made object that is discarded, disposed of, or abandoned that enters coastal and ocean waters” (NOAA). Marine debris can be thrown overboard from passing ships or washed into marine waters via stream or drains. Glass, Metal and rubber are just a few examples of marine debris that can be found floating or at the bottom of coral reefs. 

Along with external factors from negative human involvement, the internal ecological factors have been contributing to recent declines in coral reef productivity as well. These factors include invasive species, coral disease and erosion.  All of these have had a negative impact on the richness and efficiency within a coral reef’s ecosystem. 

Invasive species can impact a coral reefs productivity in multiple ways including, predation outbreaks, overcrowding, competition for food, and competition for resources such as shelter. Invasive species are defined by Reef Resilience as “a species that is non-native (alien) to an ecosystem and/or whose introduction causes, or is likely to cause social, economic, or environmental harm. Native species may also become invasive if they cause harm by dominant colonization of an ecosystem due to loss of natural controls (i.e., loss of predators or herbivores)”.  They are considered the most threating factor to marine ecosystems as they can set a reef’s ecosystem off balance entirely. Some of the most common forms of invasive species include algae, invertebrates, and fishes, with around “Eighty-four percent of the world’s marine ecosystems are already impacted by invasive species” (Reef Resilience). 

Similarly, to invasive species, coral diseases can off set a coral reefs system and bring down an entire ecosystem. Typically caused by other stressors, coral diseases “generally occur in response to biological stresses, such as bacteria, fungi and viruses, and non-biological stresses, such as increased sea surface temperatures, ultraviolet radiation and pollutants” (NOAA). Within the past decade coral diseases have increased ten fold, and their impact has left a speed bump for the restoration of reef life in many of the worlds coral reefs. Not much is known about how these coral diseases evolve yet they are documented in great detail. The yellow band disease, for example, “can rapidly spread over a coral, destroying the delicate underlying tissues”, and kill it from the inside out. After a coral’s skeleton is exposed to consuming algae and disease, it can become a fertile breeding ground for that algae and “encrusting invertebrates” (NOAA). As the algae slowly takes over the coral it “can result in the health of the entire colony”, and from which it rarely can recuperate (NOAA).

The final internal ecological factor is natural bioerosion of coral reefs. Bioerosion is defined as “the removal of calcium carbonate substrate by biological agents” (WordPress). As coral is primarily made up of Calcium carbonate, this poses a major threat. There are three major causes of bioerosion are microborers, macroborers and grazers. All of these cause a massive amount of erosion to occur on coral reefs. Microborers include microscopic organisms such as cyanobacteria, small algae, and fungi, and they bore microscopic holes into coral in order to for a sheltered area. For reference, these tiny organisms can fill up to 1.1 million school buses full of calcium carbonate in one year’s time. (Wordpress). Macroborers, similar to microborers, also bore holes into coral and other reef substrates. They however erode the skeleton of the coral and, as a result, decrease the overall strength of the coral. Bivalves and barnacles help make up this category, and they are extremely dominating in the warmer Hawaiian waters. Finally, the last source of erosion are grazers. Grazers are “mainly sea urchins and fish” (WordPress). These, although majority are trying to eat the algae on coral, happen to break large portions of coral off as well. All of these erosion contributors, have negatively impacted the growth rates and mortality rates of coral reefs around the world.  

Coral reefs have been negatively impacted by both internal ecological forces and external human impacts. As a result, coral reefs around the world are fighting extinction and are in a desperate need for preservation and restoration. In order to attempt a reversal in destruction of reef ecosystems, humans can become more ecofriendly and wiser in waste management along with controlling expansion into marine habitats. 
