The Red Sea
Sheppard, C.R.C. (2000). The Red Sea, in: Sheppard, C.R.C. (Ed.) Seas at the millennium: an environmental evaluation: 2. Regional chapters: The Indian Ocean to The Pacific. pp. 35-45
In: Sheppard, C.R.C. (Ed.) (2000). Seas at the millennium: an environmental evaluation: 2. Regional chapters: The Indian Ocean to The Pacific. Pergamon: Amsterdam. ISBN 0-08-043207-7. XXI, 920 pp., more
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Document type: Review
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| Abstract |
The Red Sea lies between about 13 and 30°N, straddling the Tropic of Cancer. It is a spreading centre, widening by a few cm each year; it is seismic, and the African and Arabian coasts mirror each other to a remarkable degree. In the north, the Gulf of Aqaba is a continuation of the Red Sea rift, but the Gulf of Suez is a shallow (<50 m) sedimentary basin. Widely known for its steep, clear-water coral reefs, the main reefal area is in fact focused in the northern half, while in the south, depth contours sweep well out from land, providing vast areas of sedimentary shallows much more suitable for mangroves and seagrasses than for reef growth. The total length of shoreline is probably more than doubled by small islands, which thus have a marked biological importance, especially in the provision of very sheltered habitat. The Red Sea was hypersaline immediately before the Holocene sea-level rise about 17,000 years ago, so the present biota is therefore relatively recent and includes numerous endemic species. Most fringing reefs extend only a few tens of metres from the steep shores in the north, but where there are old alluvial fans, and further south, they commonly extend 1 km to seaward from alluvial plains 1 to 7 km wide. Offshore, extensive series of submerged limestone platforms form the foundations for a barrier reef. Further south, fringing reefs diminish and in many places are completely replaced by broad and thick stands of mangrove and extensive seagrass beds, by muddy flats and sand deposits. Calcareous red "algal reefs" exist in the absence of coral reefs, and a very conspicuous increase in brown algae, mainly Sargassum, occurs on shallow hard substrate. Primary production is low in the north, but in the south there is considerable pumping of surface water into the Red Sea from the Indian Ocean, creating much richer conditions there. Intense evaporation removes an amount of water equivalent to a depth of 1 to 2 m per year, of which only a negligible part is replaced by fresh water, most coming from inflow through the southern entrance. The Red Sea coastline for the most part has extremely low levels of population outside a few major ports and cities, which has greatly limited the degree of coastal shoreline alteration, pollution and resources abstraction. Petroleum hydrocarbon levels are relatively high in the Gulf of Suez, where there is substantial oil and tar on shores, and refuse and beach debris is also marked in localised areas. Lack of widespread sewage treatment facilities in most Red Sea countries has resulted in extensive localised damage to coral reefs and in some areas has caused eutrophication problems in ponded or lagoonal areas, or over extensive reef flats near towns. Fishing is mainly artisanal, though purse seining and trawling activities occur in shallow areas, especially the Gulf of Suez. Fishing in most of the Red Sea has probably been mostly at sustainable levels to date, but such fisheries are very difficult to monitor and manage, and there is concern that regulations which do exist are commonly ignored. There is good potential for continued sustainable use, partly because of the existence of a regional programme and, equally importantly, because the overall population density of the coast remains very low. |
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