Direct Human Impacts on Coral Reefs: Pollution, Overfishing and Cyanide and Dynamite Fishing

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Coral cutting
Reefs are threatened 1) global warming; 2) pollution caused sewage and fertilizer; 3) coral mining; 4) industrial and agricultural run off; 5) sediment from deforestation; 6) dredging of harbors and channels; 6) the use of poisons and dynamite by fishermen; 7) commercial fishing; 8) sport fishing, scuba diving and tourism; 9) sediments from coastal development; and 10) the commercial exploitation of fish, corals, giant clams and other species.

If too many grazing fish are caught, algae grows unchecked and the coral polyps are deprived of sunlight. Careless thrown anchors and misplaced hands or fins day after day by scuba divers and snorkelers can also seriously damage fragile corals. Once destroyed by a carelessly tossed anchor, a reef needs 20 to 30 years to repair the damage.

Sediments from erosion block life-sustaining sunlight, choke the pores of sponges and causes corals to weaken and be overpowered by algae. Nitrogen and phosphorous from fertilizer causes suffocating algae blooms and increases plankton growth which can lead to population explosions of coral-damaging star fish. In some places conditions are so bad that the emphasis has shifted from documenting damage to accessing if and how the reef might be restored.

Websites and Resources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); “Introduction to Physical Oceanography” by Robert Stewart , Texas A&M University, 2008 ; Fishbase ; Encyclopedia of Life ; Smithsonian Oceans Portal ; Woods Hole Oceanographic Institute ; Cousteau Society ; Monterey Bay Aquarium ; MarineBio ; Websites and Resources on Coral Reefs: Coral Reef Information System (NOAA) ; International Coral Reef Initiative ; Wikipedia article Wikipedia ; Coral Reef Alliance ; Global Coral reef Alliance ;Global Coral Reef Monitoring Network

Reefs and Pollution

Bleached coral
Reefs have been damaged to varying degrees by pollution from factories, runoff from farms, fertilizers and pesticides and impacted by coastal development, deforestation and oil and chemical spills. Impacts from pollution can impede coral growth and reproduction, disrupt overall ecological function, and cause disease and mortality in sensitive species. It is now well accepted that many serious coral reef ecosystem stressors originate from land-based sources, most notably toxicants, sediments, and nutrients.[Source: NOAA]

Roberto Iglesias, a biologist from UNAM, a university in Mexico, and author a study on pollution in the sea in Science magazine, told Reuters, “The net effect of pollution maybe as bad or maybe worse than the effect of global warming.” Coral reefs near Cancun in Mexico that Iglesias has studied have sickly brown spots and are being engulfed by algae that feeds on sewage flowing from the resort.

Corals can flourish is surprisingly murky waters, as long tides or currents periodically sweep away sediments. Nutrients are what hurt them the most. High levels of nitrogen from sources such as fertilizer provide food for free-living algae which explode in bloom and smother other sea creatures.

Corals deal with stresses like silt and pollution by secreting mucous proteins on their outer tissues, which often attracts viruses, bacteria and fungus that feed on the mucus and sometimes even breed there.

How Land-based Pollution Threatens Coral Reefs

Many serious coral reef ecosystem stressors originate from land-based sources, most notably toxicants, sediments, and nutrients. There are numerous locations where coral reef ecosystems are highly impacted by watershed alteration, runoff, and coastal development. On islands in the Pacific and Caribbean, significant changes in the drainage basins due to agriculture, deforestation, grazing of feral animals, fires, road building, and urbanization have increased the volume of land-based pollution released to adjacent coral reef ecosystems. [Source: NOAA]

Many of these issues are made worse because of the geographic and climatic characteristics found in tropical island areas. Together they create unique management challenges. Pollution (such as, sedimentation, toxins, pathogens, increased nutrients): 1) Causes disease and mortality. Disrupts ecological functions; 2) Changes dynamics and feeding behaviors; 3) Prevents coral growth and reproduction. . Land-based sources of pollution include: 1) Failed septic systems: nutrients and pathogens; 2) Coastal development & impervious surface: sedimentation and toxins; 3) Stormwater runoff: sedimentation, toxins, nutrients, and pathogens; 4) Deforestation: sedimentation; 4) Oil and chemical spills: toxins; 5) Road construction: sedimentation; 6) agriculture: nutrients and sedimentation.

Oil Pollution Threatens Egypt’s 'Super Coral'

20120517-Corales en el Parque Marino_Motu_Motiro_Hiva_5.jpg
Coral protected in Marine park Motu Motiro Hiva
Red Sea coral have proved resilient against rising sea temperatures — but are threatened by oil industry pollution resulting from dumping toxic wastewater from Egypt's Ras Shukeir oil terminal into the Red Sea. The BBC reported: The barely treated wastewater — which is brought to the surface during oil and gas drilling — contains high levels of toxins, oil and grease. Documents, which were issued by the Gulf of Suez Petroleum Company (Gupco) in 2019 to try to hire a company to treat the water, say the pollution levels "do not comply" with Egyptian environmental laws and regulations. [Source: Ziad Al-Qattan — BBC News Arabic, November 16, 2022]

Every day, 40,000 cubic meters of this toxic water — the equivalent of 16 Olympic-sized swimming pools — is going into the Red Sea, the documents say. Dr Greg Asner, an ecologist at Arizona State University, says the information is "very alarming", showing pollution from lead, cadmium, copper, nickel and other heavy metals. "You don't have to be an expert to know that something is not right here," he says.

Analysis of high-resolution satellite images shows a wide plume of green effluent flowing into the sea, travelling up to 20 kilometers (12 miles) south into areas harbouring marine life.

Satellite analysis company Soar.Earth used remote water quality monitoring techniques to examine the plume. The company's remote sensing expert, Sergio Volkmer, says it is "not made of some algal bloom" but from something beneath the surface, such as sediments or liquid emitted locally. That same green plume is visible in the earliest satellite image the BBC could find, from 1985, indicating that the oil terminal may have been dumping "produced water" into the Red Sea for decades. It still appears in the most recent image of the plant, from September 2022.

Dr Asner, the Arizona State University ecologist, also examined the area using the Allen Coral Atlas, a high-resolution satellite tool that monitors coral reefs. He says while there are signs of a thriving ecosystem on either side of the impacted area, "suddenly you can see it's hard to see through the water" because of "something on the surface which looks like pollution". Dr Gera Troisi, a lecturer at Brunel University London who studies the effects of toxins on organisms, says compounds contained in "produced water" can react with sea water, absorb oxygen, and suffocate even the most resilient marine life. "We're suffocating them and then shielding them from the light because of all of these suspended solids," she says.

Scientists, both in Egypt and internationally, have recommended the area where Gupco operates should be included in a new extended marine protection zone in the Red Sea, to cover the whole an area known as the Great Fringing Reef. Currently about 50 percent of the reef is in the zone.

Coral Trade

Pink and red corals are among the most valued corals for jewelry. A singles necklace made with them can sell or $25,000, with a kilogram of polished coral costing up to twice that. In Japan and other places red and pink coral is harvested in water about 100 meters deep. In Japan, the red and pink coral industry employs about 3,000 people and is worth about $100 million a year. It also employs large numbers of people in North Africa, where it’s the basis of a cottage industry.

Harvests of red and pink coral have declined by 85 percent since 1980. In March 2010,The United Nations Convention on International Trade on Endangered Species (CITES), the United Nations wildlife trade body, proposed controlling the trade of red and pink coral. The measure, which was sharply opposed by Japan, targeted seven species, one in the Mediterranean and six in waters off Japan and Taiwan, along with 24 “lookalike” species to prevent accidental harvesting. But the proposal was rejected out of concerns over job losses and economic damage.

Coral drilling

How Overfishing Threatens Coral Reefs

Overfishing can deplete key reef species and damage coral habitat. Fishing, particularly unsustainable fishing, can have large-scale, long-term ecosystem-level effects that can change ecosystem structure from coral-dominated reefs to algal-dominated reefs (“phase shifts”). This results from the removal of fish that eat algae and keep the reef clean to allow for space for corals to grow.[Source: NOAA]

Many reefs have been seriously overfished. Even traditional fishing methods can destroy coral reefs. A study in Fiji by scientists from the University of Newcastle found that fishing with spears and hooks and lines killed off predators of the crown of thorns starfish, allowing them to multiply and seriously damage the reef. Great Barrier Reef Overfishing have made Queen conch, spiny lobster, whelk, red snapper and Nassau grouper commercially extinct in many places. Once abundant jewfish (grouper) have all but disappeared in the Caribbean. Overfishing also hurt stocks of fish that eat coral-damaging algae.

Coral reef fish are a significant food source for over a billion people worldwide. Many coastal and island communities depend on coral reef fisheries for their economic, social, and cultural benefits. But too much of a good thing can be bad for coral reefs.
The impacts from unsustainable fishing on coral reef areas can lead to the depletion of key reef species in many locations. Such losses often have a ripple effect, not just on the coral reef ecosystems themselves, but also on the local economies that depend on them. Additionally, certain types of fishing gear can inflict serious physical damage to coral reefs, seagrass beds, and other important marine habitats.

Coral reef fisheries, though often relatively small in scale, may have disproportionately large impacts on the ecosystem if conducted unsustainably. Rapid human population growth, increased demand, use of more efficient fishery technologies, and inadequate management and enforcement have led to the depletion of key reef species and habitat damage in many locations.

Nearshore habitats serve as nurseries for many fish. Catching young fish in nets removes them before they can help replenish the population. Traps set too close to reefs and marine debris, such as ghost traps lost nets, monofilament, and lines can damage coral reefs, which take a long time to recover. Use of non-selective gears, like nets and traps, often removes more herbivorous fishes. These fish eat algae and help keep the ecosystem in balance. Some species gather in large numbers at predictable times and locations to mate. Spawning aggregations are particularly vulnerable to overfishing. Large fish produce more young that are likely to survive to adulthood. Their absence means fish populations dwindle over time.

Seattle aquarium tank

Demand for Reef Fish

The international aquarium fish trade is worth up to $1 billion a year. Up to 20 million tropical saltwater fish are sold in the United States every year. Demand for tropical fish as pets increased markedly after the success the animated film “Finding Nemo”. The fish are stored in plastic bags in warehouses and flown from country to country. Many of the fish that are captured are very sensitive and many — perhaps most — die before they ever reach an aquarium. Those that survive endure days or weeks confined to plastic bags.

There is a strong demand for large, living reef fish for Chinese banquets. Customers at the Fook lam Moon restaurant in Hong Kong's Tsim Sha Tsuo pay $369 for a large fresh wrasse plucked from a restaurant tank.

In the West people have traditionally eaten coastal and pelagic fish such as cod and tuna while Asians have eaten these fish plus reef fish such as grouper and snapper, which live in reefs and can't easily be caught with nets. Asians also believe that a wild fish that is alive until it is eaten is superior in taste and texture to a fish that has been raised on a farms or frozen. Asians will up pay to ten times more for fresh fish that they see alive before the eat it.

The Asian economic boom in the 1980s and 1990s created a large demand for live fish. Suddenly, a delicacy once reserved for royalty and the upper classes became affordable to the masses at local restaurants. Cyanide fishing and air freight business expanded to meet the demand. The live fish trade grew steadily and by 1995, it was $1 billion, 25,000-ton a year industry.

Cyanide Fishing

Fishermen in some parts of the world, particularly the Philippines and Indonesia, catch fish by squirting cyanide from plastic bottles into crevasses in the reef. The cyanide temporarily stuns the fish so they can be easily captured by hand or with small nets, often using a crowbar to pry apart the reef where the fish hide. Fisherman in the Philippines cover their faces like terrorist for protection from jellyfish stings and can stay underwater for long periods of time thanks to hoses attached to an air compressor known as a "hookah." The poison initially does not normally harm the fish but it hurts the living coral. Fishermen also use bleach and other chemicals to get fish.

Sodium cyanide capsules are cheap and easy to obtain in Asia. All one has to do create cyanide is crush a couple of these capsules and put the powder into a spray bottle of water . Cyanide fishermen then dive around a coral reef, find they fish they want and squirt the toxic mixture in it face or skirt it in an area of the reef teeming with fish. Fishermen often store the cyanide in cans on the ocean floor to escape detection by authorities.

Long-lasting cyanide kills fish, coral polyps and other forms sea life. The cyanide kills the algae of the reef on which fish feed. Then the coral itself starts to die. Cyanide fishing is also harmful to fisherman who handle the cyanide and have to search in deeper and deeper water to find fish. Recalling his fifth experience with the bends, one Filipino cyanide fishermen told National Geographic, "I went down 70 meters [230 feet] and worked for about two hours. I came straight up. A minute after I got in the boat, I went into shock." He has been paralyzed from the waist down ever since. One in ten cyanide divers either dies or is disabled.

Cyanide Fishing Trade

The practice of cyanide fishing began in the 1960s to supply tropical fish for the international aquarium trade. Since the early 1980s many of the fish caught using the methods have gone to supply restaurants in Hong Kong, Singapore and increasingly mainland China that offer reef fish pulled from a tank. The practice reached in peak in the early 1990s when 330,000 pounds of poison was placed on 33 million coral heads a year.

Small fish like clownfish and damselfish are captured for the tropical fish trade and large fish like grouper and rock cod are caught for restaurants. Half the fish die while being transported. While cyanide fishing is illegal, the selling of fish caught with cyanide is not. Fish like flame gobies that are sold for around 50 cents a piece by the fishermen that catch them fetch up to $50 a piece retail.

Fish caught using cyanide often survive long enough to be sold at pet shops in the United States, Europe and elsewhere but often die within a couple of months after they brought home. Cyanide poisoning often acts slowly through the digestive system, attacking the liver and eating away at digestive system and respiratory system.

Sometimes large ships from Taiwan and Hong Kong provide local fishermen with "hookah” air compressors and cyanide needed to catch fish. These ships are blamed for the disappearance of large fish from reefs in Thailand, the Philippines and Indonesia.

Dynamite Fishing (Blast Fishing)

In some places people catch fish by setting off an explosive charge in the water which kills or stuns fish with its percussive blast. The fishermen then scoop up the fish when they float to the surface. The fish are generally caught not to feed their families but sell for profit.

Dynamite charges are often used to create the explosions. The dynamite blows off huge chunks of reef and kills plankton, larvae, eggs, fingerlings, coral and other life forms. Blast fishing is also done with a mixture of fertilizer and diesel, an explosive mix favored by unsophisticated terrorists.

Dynamite fishing became common place in the 1970s. Although the practice is illegal most everywhere now, it is still used in the southwestern Pacific where laws are difficult to enforce in the vast sea.

Combating Cyanide and Dynamite Fishing

Efforts are being made to educate fishermen that although cyanide and dynamite fishing may increase catches in the short run they destroy the goose that laid the golden egg in the long run. This message is delivered to children in school with puppet shows.

Environmental groups are encouraging fishermen to use traditional fishing methods and to create a sense that the reefs are a resource that needs to be preserved. Villagers are encouraged establish offshore fish farms, seaweed farms and to set up "fish-aggregation devices" — floating platforms anchored in the water that attract algae and fish.

Tests for cyanide have been developed. A campaign has been launched to screen fish for the presence of cyanide and ban the import of fish caught in areas where cyanide fishing is used.

Some places have introduced punishments such as prison sentences and heavy fines and stepped up enforcement. Not everyone is happy about the efforts. In some place fish bombers threaten authorities with automatic weapons and the same bombs they use to blow up fish.

Image Sources: Wikimedia Commons; YouTube, Animal Diversity Web, NOAA

Text Sources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated March 2023

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