Anthropogenic Effects on Coral Reefs

This topic submitted by Cassie Burns ( at 9:44 PM on 6/11/03.

Amy and Jennifer at the Skywalk in Monteverde. See other pictures from Costa Rica.

Tropical Field Courses -Western Program-Miami University

Cassie Burns
Tropical Marine Ecology
Anthropogenic Effects on Coral Reefs

Coral reefs are extremely diverse and are considered to be one of the most multifunctional and economically important coastal marine ecosystems. These reefs are productive shallow water marine ecosystems and are considered to be one of the greatest natural treasures of the world (Cesar, Herman). They are composed of lime skeletons, which are formed through successive growth and deposition of reef-building corals and coralline algae.
Each reef-building coral contains many coral polyps and symbiotic algae called zooxanthellae that live within the coral tissues. Each coral polyp is an individual coral, which withdraws into the coral skeleton during the day. The zooxanthellae photosynthesize organic compounds from sunlight and these compounds are used for food for the coral (Davidson, Osha Gray). It is considered a mutualistic symbiotic relationship because the coral benefits from the algae, but the algae also benefit from the coral. The coral produce carbon dioxide and nitrogen as a waste product, which serves as a food source for the zooxanthellae. This mutualistic relationship will not allow the coral or zooxanthellae to live without each other. Because of this relationship with the algae the corals have restricted environments. The symbiotic algae require sunlight for photosynthesis and can be easily destroyed by effects such as sedimentation, thereby killing the entire coral (Miller, Stephen).
These ecosystems are filled with the highest densities of animals on the globe and surpass even the tropical rainforests in terms of diversity (Spalding et al). Because of their immense diversity, they are of great interest to scientists, pharmaceutical companies, health professionals, and others.
Coral reefs serve many functions. These ecosystems are structurally and functionally essential for sustaining the health and productivity of more than 100 island nations (Miller, Stephen). Coral reefs form the core of livelihood for subsistence fishermen and are a source of food security in times of agricultural hardship. They act as a feeding and breeding ground for millions of offshore fish (Cesar, Herman).
Besides acting as a food source, they also function as rare jewelry and construction material. Sand and rock gathered from the coral provide a strong base for construction projects. Pharmaceuticals and industrial chemicals are gathered from various parts of the reef and the marie life that dwells on the reef. Scientists are also interested in coral reefs because of their genetic resources and research opportunities. Coral reefs also act as a natural barrier against wave erosion and help protect coastal dwellings, agricultural land, and beaches designed for tourism (Castanza, Robert et al).
Coral reefs are very sensitive to changes in conditions. Because of the abundant uses of these reefs, they are now suffering from deterioration due to natural and anthropogenic (or man-made) threats. There has been a large increase in human-induced stresses on the coral reefs (Cesar, Herman). These threats include many types of destructive fishing, sedimentation and pollution, and tourist-related damage.
Many coastal communities rely on the coral reefs as fisheries. These fisheries serve as the main (or only) source of animal protein in poor communities. Various types of invertebrates, shells, and seaweed also act as a huge source of income to these poor families. Many types of fishing are unsustainable and lead to reef destruction. There are several different types of fishing methods such as hook and line fishing, fish traps, gill nets, and spear fishing. There are also destructive types of fishing, which include poison fishing and blast fishing. All of these methods cause overfishing of the reefs. “Reef gleaning” and “Free diving” are less popular forms of fishing methods where invertebrates are collected by hand.
One popular method of fishing, known as poison fishing, is a major threat to the survival of the coral reef and has been used for centuries. Cyanide fishing also reduces biodiversity and tourism because of the effects on the coral colonies. The use of poison as a fishing method was reported as early as the 17th century. Before 1960, natural poisons were used by mixing them with pulverized fish and throwing them over coral reefs (Cesar, Herman). Currently, commercial poisons are the most popular form to use, specifically cyanide. This method is practiced in small and large-scale operations. The poison is dissolved in a plastic bottle filled with water and then squirted into the holes of coral heads. The objective of this type of poison fishing is to stun and capture fish as the coral heads are squirted. These fish are then sold as specialty fish for aquariums and also for food (Fox, Helen E. et al). Fish that are caught in the wild and sold alive are considered extremely expensive and rare.
Cyanide is a popular poison to use because of its low cost and it appears that this method is becoming more popular. Also, there has not been any evidence to indicate it is harmful to humans to eat fish that have been killed by cyanide. The poison is either excreted or partially converted by the liver into a non-toxic substance.
This type of fishing not only kills some of the fish intended for capture, but also kills the coral colonies in the process especially if poison is applied repeatedly. Along with the coral heads, other organisms and larvae are destroyed. Fish that have been exposed to cyanide experience damage to their internal organs, such as their liver, intestines, and reproductive organs. Because of the failure of these organs, many of the captured fish that are intended to be delivered alive actually die. However, because the prices for the live fish are so enormous, the method is still heavily relied upon (Cesar, Herman).
A second type of destructive fishing is known as blast fishing, or fishing with explosive devices. This type of fishing occurs when a hand-made bomb is thrown into a coral reef area with the objective of stunning any fish in the immediate area. After shocking the fish, they are gathered by hand by divers (Fox, Helen E. et al). Gunpowder was the popular choice of explosive in the past. However, the current explosive is in the form of a chemical fertilizer such as potassium nitrate or in the form of a dynamite stick. Usually, a bomb is made by filling a bottle with the explosive and some sand. Then, a wick and a blasting cap are attached (Fox, Helen E. et al).
Unfortunately, this technique causes many problems. The fishermen search for schooling reef fish and pelagic fish. Many of these fish, even schools of fish, are killed in this manner. The blast from the explosive actually kills many other species, including larvae and juveniles. The corals within distance of the blast are usually shattered into pieces. For example, one bomb made from a beer bottle could shatter a 5m2 area of stony coral (Cesar, Herman).
The coral areas that are blasted have less biomass and fewer species. This occurs because the blasts kill many of the fish, but also because the coral heads are no longer present. When the coral heads are destroyed, the larger fish have nowhere to find shelter and, either move to another location or are made easier prey because they are out in the open. Because of the effect on fish, blast fishing also results in a decrease of tourism and recreational diving. Even random blast fishing will ruin the reputation of an area for many divers (Fox, Helen E. et al).
Overfishing is a type of fishing that has a different impact on coral reefs than destructive fishing methods. There are modest forms of non-destructive overfishing that don’t have a serious effect on coral reefs. However, extreme amounts of non-destructive overfishing could alter the ecosystem. Normally, overfishing occurs with other types of destructive fishing, which causes destruction of coral reefs.
Unfortunately, destructive fishing isn’t the only cause for coral destruction. Coral mining also proves to have a devastating effect on coral reefs. Reefs have been mined for years to be used for construction material and their production of lime. The material is mostly used in the building of houses and to be used as plaster for school and government buildings. Ornamental coral trade is also a cause for the coral to be mined.
In many areas that have been mined, the result is a loss of coastal protection and the occurrence of a soft-bottom ecosystem with no corals and the presence of muddy water. Tourism is directly affected by coral mining. When coral reefs are completely mined, recreational divers will choose another location to dive.
Sedimentation and pollution are major sources of coral reef destruction. Coral is destroyed through numerous types of pollution such as: domestic waste, industrial waste, erosion, chemicals used for agriculture, and logging techniques. Sedimentation smothers corals and they cannot obtain sunlight and plankton for nutrition (Dai, Chang-Feng). The effects on coral by sedimentation are different than the effects induced through destructive fishing methods. Sedimentation slowly kills the corals because it inhibits growth and makes the corals more vulnerable to disease and death. Destructive fishing is a much quicker killing of the corals.
The increases in pollution lead to algal blooms due to the increase in nutrients. This is especially severe in areas with large populations. Also, larger populations lead to more logging and more erosion (Dai, Chang-Feng).
These are just some of the problems caused by man that coral reefs are facing today. Humans benefit either directly or indirectly from coral reefs in so many ways and need to have more understanding of the dangers of coral reef destruction (Castanza, Robert et al).

Castanza, Robert et al. “The Value of the World’s Ecosystem Services and Natural
Cesar, Herman. Environment Department Work In Progress “Economic Analysis of
Indonesian Coral Reefs”. 1996.
Dai, Chang-Feng et al. “Status of Coral Reefs in East and North Asia: China, Japan,
Korea, and North Asia”. 2002.
Davidson, Osha Gray. The Enchanted Braid “The Soul of the Sea”. John Wiley and
Sons, Inc.1998. 13-36.
Fox, Helen E. et al. “Enhancing Coral Reef Recovery after Destructive Fishing
Miller, Stephen. “Stable Nitrogen Isotope Signature as Indicators of Riverine Inputs of
Inorganic Input of Inorganic-N in the Offshore Reef Systems in the Gulf of
Spalding, Mark D., Ravilious, Corinna, and Green, Edmund P. World Atlas of Coral
Reefs: Introduction.

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