Improper Fishing Methods Silt and Polluted Runoff Tourists Coral Mining Clearing of Mangroves
Improper fishing methods used on the reef are both for human consumption as well as for the growing aquarium industry.
One widely used method to obtain live fish is the use of cyanide. Cyanide is a strong poison that could potentially kill fish, however in smaller amounts it merely stuns the fish temporarily. This method of fishing is used widely in the Indo-pacific region, such as in the Philippines and the Indonesian archipelago, to supply the fast growing aquarium industry in North America and Europe with fish. It is estimated that more than one million kilograms of cyanide has been squirted onto Philippine reefs alone. Fish caught this way die with a week or two. Larger fishes such as grouper species are also taken this way to supply restaurants in Hong Kong and other Asian capitals where the people are willing to pay high prices for the live fish.
The effects of cyanide fishing on coral reefs have been much researched on, and tests have shown that even a dilute amount of cyanide can kill coral polyps and other marine life. Corals can also be damaged when the fisherman pries reefs apart in search of fleeing fish.
Another fishing method that causes irreparable damage to reefs is blast fishing. Blast fishing involves using explosives to stun large numbers of fish at a time. Not only does it kill fish, but it also damages the reef structure itself, which may take decades to recover.
Over-fishing can cause ecological problems that can affect the entire reef and threaten it. Because all reef animals are directly or indirectly linked, a threat to one species may be a threat to all.
Human activities such as land reclamation and eroded soils due to deforestation cause seawater or waterways eventually meeting the sea to become murky due to sediments. High levels of sediment in seawater can substantially block out the sunlight that corals require for proper growth, even killing them. Sediment settles on the coral polyps as well, causing them irritation.
Water runoff containing organic wastes, phosphates or nitrates from fertilizers encourage the growth of alga mats, which compete with corals for light and space and eventually smothers them. Other chemicals from pesticides of factories may also cause problems for reefs.
Although now there is a trend for eco-tourism, tourists still sometimes have a negative impact on reefs. Ignorant tourist physically damage corals when diving or snorkeling, and encourage the local people to collect shells and coral skeletons to sell as souvenirs to the tourists.
The coral reef itself is basically limestone with a layer of living corals on the top. Coral limestone and sand are being mined for construction purposes in some Caribbean and Indo-pacific areas, taking away what took the coral colonies centuries to build.
Mangrove forests near coral reefs are import to the ecology of the reef. Without mangrove swamps to hold the silt and mud on the swamp, it is washed out to sea and eventually choke the reefs.
Silt and Polluted Runoff
Clearing of Mangroves