Red Sea coral reefs

• Category: Marine and Oceanic Biomes.
• Geographic Location: Middle East.
• Summary: The Red Sea coral reefs embody unique structural formations and are home to a high diversity of marine fauna and flora.

The coral reefs of the Red Sea have been evolving for 40 million years, ever since the breakup of the Arabian and African continental plates. The Red Sea possesses some of the most diverse and abundant coral reef ecosystems on Earth, important to the fishery and tourism industries of multiple Middle Eastern countries, and to the biota of the nearby Indian Ocean, for which these reefs often act as a nursery.

The Red Sea is a long, narrow body of water extending about 1,305 miles (2,100 kilometers), with a central trough reaching depths of more than 6,562 feet (2,000 meters) and a continental shelf that is 984 to 1,312 feet (300 to 400 meters) deep or less. The Red Sea proper is generally characterized by well-developed fringing reefs found almost continuously along both coasts but less in the southern portion. In this area, some inlets and partly enclosed bays have incomplete fringing reefs.

The northern and central portions of the Red Sea have the best-developed fringing reefs, but other reef structures—such as the atoll-like ones bordered by deep water, barrier reef structures, and offshore patch and bank reefs—are also common.

The Red Sea rift system splits into the Gulfs of Suez and Aqaba, both of which are morphologically different. The Gulf of Suez is a wide, fairly shallow—maximum depth of 279 feet (85 meters)—basin dominated by sand and sediment, with few corals or mangroves. The reefs of the Gulf of Suez are discontinuous fringing reefs along the western side, whereas the eastern side has much smaller, fragmented fringing and patch reefs. The Gulf of Eilat (Aqaba) is fairly deep, reaching a depth of 6,562 feet (2,000 meters), with varied sublittoral ecosystems, and is characterized by narrow fringing reefs and vertical dropoffs.

South of the Gulfs of Suez and Aqaba lie extensive and continuous fringing reefs extending down to Halaib on the border of Sudan. Reef complexes in the central Red Sea are found along the coast at about 2 to 6 miles (3 to 10 kilometers) offshore, on a series of narrow underwater banks of tectonic origin. In the southern Red Sea, these banks are much wider and give rise to the Suakin, Dahlak, and Farasan archipelagos, which at times resemble atolls. Beyond the banks, the seabed drops rapidly to more than 3,281 feet (1,000 meters). In the southern Red Sea, the quality, complexity, and extent of reefs decrease because of shallower bathymetry, higher turbidity, and greater freshwater input.

Sediment trapped by the immense depth and a small amount of freshwater input from rivers or rainfall contribute to exceptionally clear water in the Red Sea. The exchange of water with the Indian Ocean diminishes the effect of extreme temperatures and salinity, thus creating a suitable environment for coral reef development. The comparative calmness and lack of severe storms mean that coral growth is less restricted by exposure to wave action than oceanic reefs. Water pollution was long restricted to industrial areas where desalination plants were located, but recent observations indicate that healthy reef areas are beginning to show signs of deterioration due to poor water quality.

Biodiversity

The Red Sea has rich coral fauna, most of which are found in the central Red Sea and the Gulf of Aqaba. There are approximately 346 hard coral species in the Red Sea, of which, around 6 percent are endemic (found nowhere else). The number of stony coral species declines significantly toward the south. On average, coral diversity is greater in the Gulf of Aqaba, northern Red Sea, and central Red Sea than in the south, with nearly double the number of coral species.

The dominant genera of stony corals are Acropora, Montipora, Pocillopora, Stylophora, Pavona, Leptoseris, Fungia, Porites, Favia, and Leptastrea. Also, pipe organ coral (Tubipora musica) has been reported in the Red Sea. Geographically, coral diversity varies considerably in the Red Sea due to changes in water temperatures, salinity, sediment loading, light, and anthropogenic effects.

Other fauna and flora in the Red Sea include green (Chelonia mydas), loggerhead (Caretta caretta), leatherback (Dermochelys coriacea), olive ridley (Lepidochelys olivacea), and hawksbill (Eretmochelys imbricata) sea turtles, which reportedly use the area to breed on the Sinai coast. Giant clams (Tridacna maxima) are common, and sharks (Selachimorpha), dolphins (Delphinidae), and the vulnerable dugongs (Dugong dugon) also live near the Red Sea's coral reefs.

The Red Sea is also an important ornithological site during spring and autumn migrations for many species of storks, ospreys, terns, herons, and gulls. Reports document sixteen species of marine mammals, 210 echinoderm species (8 percent endemic), 135 mollusks species (6.5 percent endemic), 230 crustacean species (10 percent endemic), 1,700 shallow fish species (3 percent endemic), and several species of mangroves. The grey mangrove (Avicennia marina) is the most common species, though several others exist in the region, including the large-leafed orange mangrove (Bruguiera gymnorhiza), the spurred mangrove (Ceriops tagal), and the red mangrove (Rhizophora mucronata).

Environmental Threats

Destruction of wide reef areas in the northern and central Red Sea has been related to abnormally high numbers of the large black-spined urchin (Diadema setosum), a species that feeds on algal films and may damage coral and its spat; and also due to widespread white band disease and bleaching, as well as intensive predation by the corallivorous gastropod (Drupella cornus) and other snails of the Drupella genus. The two latter causes are major contributors to coral mortality of the important and dominant coral branching species Acropora hemprichii.

The once-pristine coral reefs of the Red Sea are in decline. A decrease of 20 to 30 percent in coral cover in the Red Sea from 1987 to 1996 was largely attributed to an expanding tourism industry. Other anthropogenic effects that have contributed to coral reduction include fin damage, swimming and diving, ships dropping anchor, coastal development, sedimentation, dredging, and construction of artificial beaches and desalination plants.

Among the other negative factors are sewage and nutrient-loading from hotels and resorts, high commercial boat and tanker traffic, oil spills, chemical and thermal effluents, disposal of sewage and septic tanks from dive boats, dynamiting, lobster catching, and spearfishing.

Overfishing damages reefs as it upsets the natural balance of the ecosystem by removing large predators, thus allowing population explosions of smaller species, or by removing important herbivores that graze on algal patches, allowing overgrowth of algae that outcompetes coral species for space on the substrate.

However, unlike reefs throughout the world, those in the northern region of the Red Sea have not experienced coral bleaching due to increased water temperatures caused by global warming. In 2020, researchers discovered that some corals, nicknamed "super corals," in the area could withstand extreme temperatures. For most corals, a temperature increase of 1 is enough to cause coral bleaching. These corals, however, can survive a 7 increase. The corals in the Red Sea are relatively young, which experts believe is part of the reason for this, making the region a thermal refuge for coral survival. However, by late 2023 and early 2024, bleaching events were increasing in the Red Sea, including the Gulf of Aqaba. Several organizations continue efforts to limit the death of the coral reefs in the Red Sea caused by climate change, including the Transnational Red Sea Center (TRSC) and the General Organization for the Conservation of Coral Reefs and Turtles in the Red Sea (SHAMS).

Bibliography

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