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Context

• The Red Sea's spectacular coral reefs face a new threat. Marine biologists warn—the mass death of sea urchins that may be caused by a mystery disease.

Red Sea Coral Reefs

• Red Sea coral reefs are the northernmost in the Indian Ocean. Most of the Red Sea coast is rimmed by shallow submarine shelves and extensive fringing reef systems, by far the dominant reef type found here.
• Red Sea fringing reef platforms are over 5000 years old, and the entire coastal reef complex extends along some 2,000 km of shoreline.
• Most such reefs grow directly from the shoreline. The dominant, most actively growing corals include most notably highly branched species of the genera Acropora and Porites.
• Such Red Sea coral reef formations are almost certainly the result of the active and unusual tectonic forces that have been at work here for millennia and continue today.
• There are a few true atolls in the Red Sea (several off the coast of Sudan), but no true barrier reefs.

Characteristics of Red Sea Coral Reefs

• Red Sea corals have developed an unusually high tolerance to the extreme temperatures, salinity, and occasional turbidity (caused by huge seasonal dust storms) that occur in the region. Such conditions that would be lethal or highly damaging to most hard corals found elsewhere.
• Also, water clarity is exceptional in the Red Sea because of the lack of river discharge and low rainfall. Thus, Red Sea reefs are not heavily impacted by the suspension and dissipation of fine sediments that plague reefs in tropical oceans near large land masses.
• Red Sea coral reefs are particularly well developed in the north and central portions (off the coasts of Egypt, Saudi Arabia, Sudan), with large sizable offshore reef complexes containing small islands, fringing reefs, and a variety of reef-associated habitats.
• Further south, coral growth is somewhat inhibited by the influx of nutrient-laden water where the Indian Ocean enters the Red Sea. The surface waters of the more southerly areas are also subject to far greater mixing with deeper water caused by strong winds coming off a high mountainous coast.
• In general, the marine biota of Red Sea coral reefs is characterized by high endemism. For example, of the 1200 or so Coral Reef Fish species recorded, about 10% are endemic (found nowhere else).
• Despite the extreme conditions characteristic of the region, Red Sea coral reefs are generally healthy. There is usually minimal coral bleaching evident, although some localized outbreaks are reported from time to time.

Sea Urchins

• Sea urchins are members of the phylum Echinodermata, which also includes sea stars, sea cucumbers, sand dollars, brittle stars, and crinoids.
• Like other echinoderms, they have five-fold symmetry (called pentamerism) and move by means of hundreds of tiny, transparent, adhesive "tube feet".
• Urchins typically range in size from 3 to 10 cm, but the largest species can reach up to 36 cm.
• Sea urchins are benthic creatures and eat plant and animal matter, largely preferring kelp, algae, and sponges in their rocky habitats, as well as decaying matter that settle down from the water column.

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