Apron reef — short reef resembling a fringing reef, but more sloped; extending out and downward from a point or peninsular shore.
Fringing reef — reef extending directly out from a shoreline, and more or less following the trend of the shore.
Barrier reef — reef separated from a mainland or island shore by a lagoon; see Great Barrier Reef.
Patch reef — an isolated, often circular reef, usually within a lagoon or embayment.
Ribbon reef — long, narrow, somewhat winding reef, usually associated with an atoll lagoon.
Table reef — isolated reef, approaching an atoll type, but without a lagoon.
Atoll reef — a more or less circular or continuous barrier reef surrounding a lagoon without a central island; see atoll.
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Satellite image of a part of the Great Barrier Reef, off the East coast of Australia. Photo courtesy of NASA.
Humans continue to represent the single biggest threat to coral reefs. In particular, land-based pollution and over-fishing are the most serious threats to these ecosystems. The live food fish trade has been implicated as one driver of decline due to the use of cyanide in the capture of fish. Rising water temperatures produce toxins in the coral tissue, due to bleaching.
High levels of land development have also been threatening the survival of coral reefs. Within the last 20 years, the once thick mangrove forests, which absorb massive amounts of nutrients from runoff caused by farming and the construction of roads, buildings, ports, channels, and harbors, are being destroyed. Nutrient-rich water causes algae to thrive in coastal areas in suffocating amounts, also known as algal blooms.
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