Arabia Seas. a Global Representative System of Marine Protected Areas
Total Page:16
File Type:pdf, Size:1020Kb
MARINE REGION 11 Arabian Seas Anthony W. Chiffings BIOGEOGRAPHY AND BIODIVERSITY gin to be mined (Hanna 1983a; Nawabi 1983). The Arabian Seas Marine Region includes Ecological problems also result from the marine areas from Djibouti to Pakistan, in- loss and degradation of productive coastal cluding the northern part of Somalia, the habitats caused by coastal landfill, dredg- Red Sea, the Gulf, and parts of the Arabian ing, and sedimentation. In some Gulf States Sea.1 (for example, Saudi Arabia), 40 percent of Coastal and marine environments the coastline has now been developed, and throughout the Arabian Seas Region are a significant proportion of the shoreline of subject to increasing human pressures, countries such as Kuwait and Bahrain is arti- many of which appear to have resulted in ficial. Loss of habitat extends to other parts harmful environmental effects. Oil, phos- of the region and to the wider Indian Ocean phate mining (Hanna 1982, 1983a), and do- where approximately 50 percent of man- mestic, urban and industrial pollutants are a grove forests may have been lost over the problem in several areas in the Gulf and the last 20 years (IUCN/UNEP 1985c). Overfish- Gulf of Aqaba and have resulted in local ing is a major concern in all areas of the habitat degradation, eutrophication and al- region. gal blooms. Throughout much of the Ara- Degradation of coral reefs from heavy col- bian Seas the coastal zone is becoming a lecting and other recreational and tourism repository for solid wastes. In the Red Sea, uses is becoming widespread, particularly the ecological effects from oil exploitation, in the Red Sea (Hanna and Ormond 1982; phosphate mining (Hanna 1982, 1983a,b), Ormond 1981; Hanna 1991). Fishing and and industrial inputs (such as from mining) hunting of adult turtles and birds (and their are of increasing concern, and will become eggs) is extensive in some areas (Hanna more so if deep-sea metalliferous mud be- 1994). The effects of land-based activities such as nutrient and sediment runoff from 39 40 A Global Representative System of Marine Protected Areas phosphate mining (Hanna 1982; Hanna and rainfall may amount to as little as 10–15 mil- Ormond 1982), agriculture and grazing, and limeters per year, whereas along the coast- reductions in freshwater seepage due to line its estimated range is from a few groundwater extraction are also contribut- millimeters per year along the northern part ing to degradation of coastal environments. of the western shore, gradually increasing to 180 millimeters at Suakin (19°N) (Ed- Oceanography wards 1987). These unique features have contributed to making the Red Sea vulner- The Arabian Seas Marine Region is a natu- able to the impacts of human activities. ral unit created by the geological history The Gulf, in marked contrast, is a shallow that formed the Arabian peninsula and its sedimentary basin with an average depth of associated regional seas and the maritime 31 meters. Freshwater is supplied by the climate that is dictated primarily by the sea- Shatt el Arab and some Iranian rivers. Sur- sonal monsoons associated with the Asian face water temperatures range from 32– continent. 33°C in summer to 22–24°C in winter in the Map 11 shows ideal summer and winter south but only 16°C in the north. Salinities wind distribution and surface circulation pat- generally range from about 38–40o/oo, in- terns for the Indian Ocean. Wyrtki (1973) creasing to more than 60o/oo in areas such and Shepherd, Price, and Roberts (1992) as the Gulf of Salwa, but falling to around provide concise descriptions of the physical 37o/oo in the Gulf of Oman. Tides in the Ku- oceanography of the Indian Ocean, includ- wait region range up to 3.5–4.0 meters, ing the monsoon gyre. whereas south of Al Kobar, on the Saudi The Red Sea, a product of deep-ocean coast, they are is less than 1 meter. Even rifting, extends for 2,100 kilometers from so, strong tidal flows occur throughout the Suez to the Strait of Bab el-Mandeb, which Gulf. connects it with the Gulf of Aden and the In- The Gulf of Oman is deep and largely dian Ocean. The Sea has an average depth open to the influence of the northern Indian of 500 meters, with a maximum of over Ocean (Arabian Sea). The oceanic coasts 2,000 meters, and is noted for some of the of Yemen and Oman are completely open hottest and most saline seawater in the to the influence of the northern Indian world. In the south, surface water tempera- Ocean and are, in parts, subject to large tures exceed 30°C in summer, while salinity oceanic upwellings that bring nutrientrich is 40o/oo in the north in winter and up to water to the surface, causing high productiv- 46o/oo in the middle of the Suez Canal. ity. The Red Sea has a number of unique fea- The coast of Pakistan constitutes the tures. It is the warmest and most saline of northern boundary of the Arabian Sea, with the world’s seas. It has no permanent in- oceanic influences dominating over those flowing coastal rivers or streams, only sud- of the continent, which is essentially a sub- den brief torrents, and mostly northwesterly tropical dessert. River flows are monsoonal, prevailing winds, which contribute material with the only major freshwater input coming to the sea floor. The nature and distribution from the Indus, at the eastern extremity that of sediments are unlike those in other seas. discharges some 200,000 gallons of water The Red Sea is partially isolated from the and 450 million tons of suspended sedi- open ocean (Hanna, personal communica- ment annually and forms the Indus cone, a tion). It is located in an arid, tropical zone. subaqueous delta 1,500–2,000 kilometers Rainfall in general is sparse and varies long (Pernetta 1993). widely, with particular areas receiving no Currents in the Gulf and the Red Sea rainfall for months or years. Over the sea, largely result from density gradients in the Marine Region 11: Arabian Seas 41 water column. Evaporation in the Gulf changes in water level that are more signifi- causes movement of water inward through cant. the Strait of Hormuz. Surface salinity is high- The Arabian Sea coastline of the Arabian est in the two large southern Gulf embay- peninsula has a tidal range of 1.5–2.5 me- ments where greatest evaporation occurs. ters over most of its length, but these tides Denser water formed in these regions sinks are thought to be subordinate to the persist- toward the Strait of Hormuz while less- ent impact of high-energy waves (Shep- dense water enters along the surface and pard, Price, and Roberts 1992). The northern edge of the Strait, moving in a Pakistani coast has tides of up to a 3.5-me- counterclockwise surface current and leav- ter range (Pernetta 1993). ing the Gulf in the deeper and southern part of the Strait (Sheppard, Price, and Roberts Coastal Geography and Geology 1992). Currents in the Arabian Sea result from The main body of the Red Sea lies in a rift the removal of surface water during the valley separating the African and Arabian summer monsoon and its replacement by plates (Drake and Girdler 1964; Quennel cooler upwelling water (Sheppard, Price, 1958). Plateaus and mountains rise steeply and Roberts 1992). to more than 1,000 meters above sea level Surface water density in the Red Sea north of Jeddah and 3,660 meters in rises with a fall in water temperature to the Yemen. The coastal plain is from 2–50 kilo- north and evaporation causing increased meters wide and slopes up gently to the salinity. Decreasing temperatures and east until it meets the mountains. The moun- evaporation in the Gulf of Suez result in the tains are deeply cut by valleys but streams formation of dense water that turns under flowing in the uplands fail to cross the and is returned southward in the deep Red coastal plain to reach the sea (Schwartz Sea (Sheppard, Price, and Roberts 1992). 1982). Circulation and exchange in the Red Sea The Gulf of Aqaba is 170 kilometers long is not well understood, but is thought to be and 14–26 kilometers wide and forms part quite complex as a product of the low-en- of the Afro-Syrian Rift System with steep ergy regimes involved. In simple terms walls dropping to great depths (2,000 me- though, in winter (September–June) sur- ters in places). It is separated from the Red face water is driven into the Red Sea by pre- Sea by the 6-kilometer wide Straits of Tiran. vailing winds from the southeast, beneath Fringing reefs lie along most of the Sinai which there is a deep outward flow of more Peninsula shoreline (Hanna, personal com- dense, saline water. During summer, pre- munication). vailing winds change to the northwest, driv- The Gulf of Suez is a wide, shallow basin ing the upper water layer out of the Red with an average depth of 20–30 meters, Sea over a deeper inward flow from the greater depths in the central trough, and a Gulf of Aden. Net outflows are 10 percent depth of 90 meters at the entrance to the higher in salinity, and balance the effects of Red Sea. The fringing reefs in the Gulf of evaporation in the Red Sea. Suez are not as well developed as those in Tides in the two regional seas are in the the Gulf of Aqaba. range of 0.5–1.5 meters.