BOX 5-4 Gulf War Spill, Arabian Gulf
Over a period of about four months from January-March 1991, crude oil was released into the Arabian Gulf from five tankers, a major tank field, and several offshore terminals, refineries, and battle-damaged tankers as part of the Iraq-Kuwait conflict. Though the actual volume of release will never be known, the best estimate is about 1,770,000 tonnes (520,000,000 gallons) (Tawfiq and Olsen, 1993), making it the largest oil spill in history and three times as large as the next largest spill (the 1979 Ixtoc well blowout in the Gulf of Mexico). Although the massive slicks were initially predicted to spread throughout the Arabian Gulf and out through the Gulf of Hormuz, a seasonal shift in wind patterns held the bulk of the oil along the shoreline between the Kuwait border and Abu Ali Island near Al Jubail, a distance of about 175 km. The oil fate was estimated by Tawfiq and Olsen (1993) as follows: 40 percent evaporated; 10 percent dissolved/ dispersed; 10 percent recovered in Saudi Arabia; 15 percent stranded on shore in Saudi Arabia; and 25 percent unaccounted for. There was concern that a significant portion of the unaccounted for oil sank; however, Michel et al. (1993) did not find evidence for any significant sunken oil in the nearshore subtidal zone during diving surveys (197 dives) offshore the most heavily oiled shorelines and bays in Saudi Arabia. None of the researchers studying the Arabian Gulf after the spill reported large-scale oil contamination of bottom sediments (Price and Robinson, 1993).
The spill significantly affected shoreline habitats, with 707 km of shoreline oiled in Saudi Arabia alone, including 124 km of marshes (Gundlach et al., 1993). Very little shoreline cleanup was attempted. An estimated 50-100 percent of the intertidal biota were killed (Jones et al., 1996); in heavily oiled marshes, less than 1 percent of the plants survived (Böer and Warnken, 1996). Followup shoreline surveys in 1992 and 1993 showed that the stranded oil had penetrated up to 40 cm into the sediments, with liquid oil filling burrows in muddy sediments (Hayes et al., 1995). The heavy surface oiling formed persistent pavements along the upper intertidal zone and on the tops of mid-tide bars that showed little evidence of erosion six years after the spill. The surface pavements slowed the rate of subsurface oil weathering and physical removal, effectively sealing the subsurface oil in place. Intertidal species diversity in the lower intertidal zone on sandy and muddy substrates was 50-100 percent of controls by 1994, whereas in the upper intertidal zone, species density and density was 0-70 percent of unpolluted sites (Jones et al., 1996). As of 1997, there was little evidence of recovery of heavily oiled marshes. Much of the heavily oiled shoreline occurred along sheltered bays with little exposure to waves and currents. Thus, natural removal of the stranded oil will be very slow, and full recovery of intertidal communities will likely require decades.
Amazingly, no significant long-term impacts to subtidal habitats and communities were observed, including seagrass beds, coral patch and fringing reefs, unvegetated sandy and silty substrates, and rocky outcrops (Kenworthy et al., 1993; Richmond, 1996). Kuwait crude forms a very stable emulsion that resulted in thick surface slicks that stranded onshore rather than mixed into the water column. Impacts to shrimp stocks, however, were severe; in 1992 spawning biomass dropped to 1 percent and total biomass dropped to 27 percent of pre-war levels (Matthews et al., 1993). Causes of this collapse were attributed to a combination of mass mortality of eggs, larvae, and postlarvae resulting from oil exposure during the entire spawning season, emigration of adults out of the oiled areas, mortality of adults, heavy fishing of adults and juveniles thus further reducing the spawning biomass, and decrease in water temperatures and light intensity because of oil fires smoke and haze.
At least 30,000 seabirds are estimated to have died as a result of the spill. Although the oil spill killed an estimated 25 percent of the 1991 Saudi Arabian breeding population of the endemic Socotra cormorant, these colonies tripled in population by 1995 (Symens and Werner, 1996). Internationally important breeding tern populations in Saudi Arabia and Kuwait escaped direct oiling impacts in 1991 (70,000 pairs breed on offshore islands in summer), but severe declines in breeding success in 1992 and 1993 resulted from an acute shortage of food that was attributed to the oil impacts on fish recruitment (Symens and Alsuhaibany, 1996). In 1994, breeding success was high. During the spill, shorebird populations were reduced by up to 97 percent; however, it is not known whether the birds avoided the noxious oil or were driven away by a lack of food and found good feeding areas elsewhere, became oiled and died, or died from starvation (Evans et al., 1993). The greatest shorebird impacts, however, were likely the indirect effects of long-term degradation of intertidal habitats and the loss of their food supply.