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Millions of barrels of oil sloshing around shallow, fertile waters amid the confusion of war – a crueller blow to a marine ecosystem is hard to imagine. But will the oil spillage in the Gulf prove as damaging as was originally feared? The initial newspaper and television reports focused, perhaps predictably, on the threat to dugongs, turtles and wading birds. The ultimate fate of the ecosystem, though, does not rest with individual Gulf species, however endearing they may be. It lies with the marine habitats at the base of the food chain.

Assessing the likely damage to these habitats is far from easy. Over the past few weeks, uncertainty over the amount of oil spilled and its whereabouts in the Gulf has bred confusion aplenty. Even the number of sources of spilt oil within the military zone has been unclear. Military activity continues to hinder access to many of the worst-hit areas, particularly near the Kuwait coast.

Yet two things look reasonably certain. First, the biggest long-term threat to the ecosystem would come from any damage to the oxygen-producing plants and algae that live on the Gulf’s sea bed. Without these ‘primary producers’ the ocean would be unable to support its other life forms. Secondly, after any contamination of the desalination plants, the hardest blow to the local human population would result from any damage to the Gulf’s fisheries. For centuries these have underpinned a rich coastal culture .

In many ways the Gulf is an odd ecosystem. Highly stressed by enormous temperature fluctuations, it is unlike most tropical seas, despite being only 24 to 30 degrees north of the equator. Contrary to many press reports, coral reefs and mangroves – the very habitats that epitomise tropical seas – are quite scarce. The region is instead dominated by less spectacular, but no less important, seagrasses and algae. To understand how oil might affect these habitats, one needs to know something about their whereabouts in the Gulf and their relationship to the Gulf’s climate.

The Gulf’s marine life is shaped more by its extreme climate than anything else. Air temperatures may drop to freezing in winter and rise to over 50 degrees in summer. Surface water temperatures generally range from 15 to 35 degrees, while water in the vast areas of shallows follows the air temperature much more closely. Evaporation is intense, so salinity is much higher than in the open ocean; in mid-Gulf it stands at around 40 parts per thousand, while in the shallows it can rise to double that amount and in the lagoons it soars to around 200 parts per thousand.

Next come winds, currents and tides. There is an anticlockwise drift in the Gulf, but it is so gentle that surface water movement – and movement of any floating oil – is influenced by winds more than by any underlying currents. The winds are generally northerly or northwesterly, which means that oil spilled in the Kuwait region will generally be pushed down the Saudi Arabian coast to Bahrain.

During February the largest slick (from the Mina al Ahmad terminal in Kuwait) moved much more slowly down the Saudi coast than expected. With access to most beaches limited, first-hand information about the amount of oil coming ashore and its impact on wildlife, particularly birds, remained scarce. Reports now suggest that the oil has begun to fragment and drift beneath the surface. In the coming weeks the slick is likely to move past Bahrain and Qatar.

The region has moderate tides of 1 to 4 metres which, together with its northerly winds, move and sort fine-grained sediments into mud flats. Sand bars, also fashioned by winds and tides, greatly extend the mud flats by trapping more fine sediments. The most extensive flats are at Kuwait Bay, Dawhat at Musallamiyah, Abu Ali, Tarut Bay, and the large Gulf of Salwah south of Bahrain.

These factors act together to produce a huge intertidal zone, and beyond that an even larger ‘sub-tidal’ expanse of shallow waters. In many parts of the Arabian Gulf the intertidal zone is so wide (up to 2 kilometres) that the land-sea boundary blurs almost to extinction. In the sub-tidal zone, the water remains only a few metres deep for many kilometres offshore.

The Gulf’s intertidal zone and adjacent shallow waters lie at the heart of its ecosystem. They are also extremely vulnerable to the effects of the spill. Within the Saudi sector, almost a fifth, or 29 000 square kilometres, is intertidal or less than 5 metres deep. Proportions are similar in the Kuwait sector where half the shore line is fronted by a muddy intertidal zone up to 5 kilometres wide.

Marine habitats at risk

The term ‘critical habitats’ is often used to describe biological communities in the Gulf. The concept has the advantage that it draws attention towards habitats and away from popular species. But it has the disadvantage of appearing to diminish the ecological importance of other habitats. In the semi-enclosed Gulf, all habitats, whether dubbed critical or not, are probably interlinked and vital.

Although the Gulf is part of the Indian Ocean, it has only about one-quarter of the species known for the Indian Ocean and Red Sea. It still has a diversity almost as great as the Caribbean, however. And, unlike the Indian Ocean and Red Sea, its organic productivity is extremely high, thanks to its extensive shallow waters. Shallows are ideal for algae and other primary producers that require light for photosynthesis. The Gulf’s productivity depends more on the marine life of its seabed than on the marine life nearer its surface.

There is another difference between the Indian Ocean and the Gulf: while the open ocean boasts a wealth of genuine coral reefs, the Gulf has few. In the western Gulf, coral reefs are small and fringing reefs completely absent, because of the muddy, gently sloping shore. Offshore the picture changes. A swath of reefs sweeps southward, becoming most expansive off the coasts of Saudi Arabia and northern Bahrain.

Much anxiety has been voiced over the impact of the oil spill on coral reefs. However, their limited size and contribution to organic productivity means they are far from being pivotal to the health of the ecosystem. In fact, what are commonly referred to as reefs in the Gulf are often not coral but limestone mounds and domes covered with algae. These predominate because algae is better than coral at withstanding climate extremes.

Yet it would be a mistake to dismiss the reefs completely. They play a part in sustaining biological diversity and provide a measure of protection against tidal erosion for some of the cays and islands that are important as breeding grounds for turtles and seabirds. Because they exist in a highly stressed ecosystem, they are also of special interest to marine biologists – for example, in assessing the possible effects of global warming on reefs in other parts of the world.

Mangroves cover only a small area of the Arabian coast, though they are more plentiful in some of the embayments along the Iranian shore. Their ecological importance lies in their ability to stabilise soft marine substrates and in the habitat they provide for invertebrates. Salt marshes, such as those containing the famous tall reeds seen in the delta of the Tigris and Euphrates, contribute little to the total organic productivity of the Gulf’s marine ecosystem. They are far more important as breeding and spawning areas.

One of the most important components of the ecosystem is the seagrass that carpets the shallow waters of the sub-tidal zone. Three species of seagrass, all highly productive flowering plants, are common. Off Bahrain, as much as two-thirds of the shallow sub-tidal zone looks from above to be covered by seagrasses, though their patchiness is such that the actual cover is probably about half this. Coverage is just as great in some bays of Saudi Arabia, where seagrasses intermingle with benthic diatoms (simple algae), which also live on the adjacent, grass-free patches of coarse sub-tidal sand. In Bahrain it is the sub-tidal sands rather than the seagrass beds which support the greater diversity of invertebrates.

Some less obvious habitats are just as important. Blue-green algal mats , for instance, cover large areas of intertidal and shallow sub-tidal zones but are commonly ignored because they are visually unspectacular. Yet they support diverse colonies of invertebrates, at least where the salinity is bearable. Ultimately they may be as important as the seagrasses to the Gulf’s organic productivity and integrity.

Little is known about the deeper Gulf waters, which are mostly muddy and dominated by marine worms and bivalves. From depths of around 20 metres onwards lies what is termed ‘deep sea mud’, one of the largest Gulf habitats. Here, not enough sunlight seeps through for much photosynthesis to occur. Nevertheless, over 600 invertebrate species have been found in sea mud between Bahrain and Qatar – more than in the shallower seagrass beds. Rocky outcrops in the mud allow sponges, anemones, hydroids and related organisms to thrive, too, as well as commercially important pearl oysters.

The extent of the long-term damage to these habitats depends, of course, on where the oil passes. If northerly winds push it onto the vast intertidal areas, as they seem to be doing, the immediate damage to organic productivity – and oxygen production – could be considerable. If most oil sinks in deeper water, the damage will be less, since the primary producers will be less affected.

The susceptibility of different habitats varies considerably. Because oil floats, at least initially, it is the intertidal regions which are the most vulnerable to coating. Mangroves are especially susceptible because their aerial roots are easily smothered. The blue-green algal mats with their mixtures of plankton, diatoms and bacteria are also at risk.

A huge blanket of oil is known to be drifting across vast stretches of the Gulf’s shallowest waters. Current conditions obviously make it difficult for biologists to assess either the slick or its effects in any detail. Wherever it lies, though, it must be blocking out at least some sunlight and reducing photosynthesis on the sea bed.

In the waters just below the surface, a more serious problem could be direct poisoning of free-floating plankton by the toxic, soluble components of oil. Any use of dispersing agents might exacerbate this effect. Aside from any adverse ecological effects, however, chemical dispersants are unlikely to be used in the Gulf as initial tests there have shown them to be ineffective. The eggs of most tropical fish are buoyant, so they, too, are likely to come into close contact with any oil floating over shallow spawning grounds. The locations of many of these grounds are uncertain, but shrimps are known to spawn in or near the seagrass beds off Safaniya, Saudi Arabia. Spawning of shrimps and other invertebrates takes place in spring.

Precious little is known about the consequences of oil sunk in the deeper muds in the Gulf. It is assumed, but not known for certain, that the oil slick released from the Nowruz platform during the Iran-Iraq war in 1983 ended up in deep water in the central Gulf. But its ecological impact is still largely unknown.

The effect of oil on coral reefs is also uncertain. It is known that oil on a reef flat at low tide can cause damage and inhibit breeding. In the mid-1980s, for instance, a spill near the Smithsonian research station in Panama reportedly resulted in extensive damage and mortality in shallow-water habitats. By contrast, the damage caused by spills over several other coral reefs, including some in the Red Sea, was reported to be minimal after six months.

It will simply not be possible to clean up many of the Gulf’s habitats once they have become contaminated by oil. Access is limited, and physical removal so difficult that greater damage may be done by trying. Heavy machinery may be used to scrape oil off beaches but on thousands of hectares of soft blue-green algal flats it will be useless. The priority clearly is to prevent oil from reaching the important areas.

In the first weeks of the current disaster environmental agencies from Saudi Arabia and elsewhere made urgent efforts to deploy booms, initially around desalination plants. Booms would be most effective in closing off embayments of flats, mangroves and marshes. Open shoreline is much harder to deal with, as are reefs, most of which exist in large mosaics of shallows that are difficult to reach.

It would be a mistake to assume that the massive spill of oil has taken place into a sea which is otherwise in pristine condition. In the first place, oil spills themselves are common, though they are usually small. Over 10 spills per year were reported in Kuwait between 1965 and 1976. Subsequently, as much as 69 tonnes have been reported spilled in a single year. When unreported accidents and runoffs are included the real total must be higher still.

Corresponding information for Saudi Arabia is scarce but, according to some estimates, operational oil spills there are much more frequent. Many parts of the Saudi shoreline are oiled to a degree generally referred to as moderate or heavy. A survey carried out in 1986, for instance, revealed tar balls at well over 70 per cent of a total of 53 sites inspected along the Saudi Gulf coast. Localised tar sheets, or ‘pavements’, have also accreted in many places.

Yet oil was not the only problem before the current spill. According to a series of studies commissioned by Saudi Arabia and carried out by the World Conservation Union and the UN Environment Programme in the 1980s, landfill, or ‘reclamatation’, and dredging posed an even greater threat to the Gulf shores. The two operations commonly go hand in hand: material is dredged from the shallow sea for depositing on, and extending, the land. About 40 per cent of Saudi Arabia’s Gulf shoreline has been subjected to landfill, dredging or both. Greater areas still have been affected by artificially raised levels of sedimentation, an often fatal stress for tropical marine life.

With the coastline habitats already battered, the current oil disaster could be particularly damaging. The last few years have seen shrimp populations fall substantially. While this is partly due to overfishing, the effects of landfilling of important breeding or feeding grounds cannot be overlooked. The current spill might accelerate this decline . The first casualty of oil spilled from Iraq or Kuwait is likely to be one of the Gulf’s less infilled areas – the northern Saudi Arabian shore.

The consequences of the oil spills are likely to appear in at least two phases. First, and most obvious, is the immediate smothering of intertidal habitats and air-breathing vertebrates . In the past few weeks we have heard many reports of these creatures being killed in large numbers, but first-hand information about the extent of the damage has been scarce. Then, if the breeding grounds of fish and shrimp are heavily struck, a decline in fisheries may become apparent over the next three years. If, as seems likely, several key spawning grounds have already been landfilled, and the oil does pass over the remaining spawning grounds, this decline could be extremely sharp.

Predictions of recovery times from both kinds of damage are equally difficult. Here the Gulf is helped by its anticlockwise drift, which could help recolonise the polluted habitats by recruiting marine life from the safer quarters of the Iranian shore, where good reefs and mangroves are found. Though heavily oiled mangroves in the hard-hit western Gulf might never recover, lightly contaminated seagrass beds might do so after a year or two.

The intense military activity in the Gulf poses a host of other threats to the marine and terrestrial environment. Not only oil, but other toxic substances could escape from the numerous petrochemical and other industrial plants sited around the Gulf coast. A study commissioned by Greenpeace shows that, collectively, these harbour large repositories of more than 20 toxic substances, including chlorine and phosgene gases and compounds such as benzene, phenol, hydrochloric acid, sulphuric acid and carbon disulphide. If these pollutants were released, their effects on wildlife could ultimately be greater than the effects of oil.

Another serious problem is atmospheric pollution from burning oil. The hundreds of oil fires started in Kuwait could lead to widespread pollution of land and sea (see ‘Desert fires cast a shadow over Asia’, New ÐÓ°ÉÔ­´´, 12 January). Smoke production could blanket incoming solar radiation, while the oxides of nitrogen and sulphur produced in the fires will produce acid rain. The likely effects of these pollutants on the marine ecosystem cannot be predicted with certainty.

Nor, it must be emphasised, can the full effects of the oil spillage. While we know enough about the marine biology of the Gulf to make some assessment of the likely damage, there are too many variables for us to be sure of how the ecosystem will ultimately respond. There are also huge areas, such as the entire Iranian coastline, for which biological data are virtually nonexistent. The Gulf’s ecosystem might turn out to be more robust than our picture of events implies, or rather more vulnerable. Moreover, aside from purely scientific considerations, any prognosis about oil pollution in the Gulf could be rendered wildly inaccurate by what is perhaps the biggest variable of all – the course of the war

Charles Sheppard and Andrew Price lecture at the Centre for Tropical Coastal Management Studies at the University of Newcastle-upon-Tyne. Their book Marine Ecology of the Arabian Seas is due to be published by Academic Press later this year.

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1: A way of life under threat

The fisheries of the Gulf, particularly for shrimp, are of great cultural and economic importance. For centuries they have provided a livelihood for coastal communities, and the use of simple fishing traps set on the intertidal zone continues today. Local fishing craft, now motorised, form the other main component of the present-day fishery. In the Gulf as a whole there are more than 1000 small motorised vessels, a fleet that has been growing steadily since the early 1960s. Initially only shrimp were captured, whereas nowadays fish are also taken. Total landings for the Gulf for 1986 were estimated to be about 14 000 tonnes of shrimps and 335 000 tonnes of other shellfish and finfish.

The pearl fisheries of the gulf were once world famous, but declined in importance after the advent of cultured pearl industry. Seagrass and algal beds are favoured habitats for juvenile pearl oysters

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2: Algal mats that feed the sea

Algal mats are not principally made of algae, although the name has stuck. They are among the most important and least noticed components of the shallow waters of the Gulf.

The mats are made from a collection of simple organisms that grow on soft marine substrates. Their main components are cyanobacteria, prokaryotic organisms that are closer to bacteria than to algae. They are highly productive, and their growths are variously called blue-green mats, cyanophyta mats or cyanobacterial mats. They are not blue-green in their natural habitat but appear as crusts of grey or brownish material overlying the muds. The mats are made up of 20 to 30 species of cyanobacteria with a similar number of diatoms, green algae and anaerobic bacteria, growing in mixed communities.

The mats are photosynthetic and they can grow rapidly, producing substantial amounts of organic material. In this, they are helped by the fact that cyanobacteria also fix nitrogen, so their productivity is not limited by this important nutrient which is typically in short supply in tropical seas.

On the mud flats, algal mats usually grow in a continuous cover from the highest intertidal region to the shallow. From time to time the mats dry out, and the crust breaks up into polygonal shapes with crisp, grey, upturned edges. From these it is simple to observe that the living crusts are a few millimetres to 2 or 3 centimetres thick.

Algal mats have an extraordinary ability to survive extremes of environment. They withstand desiccation and prolonged baking under the sun to temperatures of over 50 degreesC which in the Gulf may be inflicted on them for several weeks at a time. They thrive in the salinity of the Gulf, but also carpet the muds of enclosed bays where salinity exceeds 200 parts per thousand. When dried the mats rest in a dormant state until water inundates them again; when they rapidly revive and resume growth into a contiguous and slippery organic mat. Various adaptations have allowed them to endure such conditions, including the secretion of material which encapsulates the cells to prevent fatal desiccation.

It is this little-studied community which provides the foundation for enormous densities of invertebrates, which in turn are the food for higher orders of animals. Some of these, such as fish and shellfish, are of direct economic importance. The most spectacular might be the wading birds which pause on these mud flats on their twice-yearly migrations.

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3: The creatures that hit the headlines

Several groups of mammals and reptiles thrive in the fertile waters of the Gulf, and it is on them that much of the effort to avoid environmental disaster is likely to focus.

Many thousands of air-breathing dugongs live in the shallow waters of the Gulf, particularly near Bahrain. Although their presence has been known for a long time, it was only in the mid-1980s that vast herds were discovered. A group of about 700 were sighted between Bahrain and Qatar, and the fertile waters of the United Arab Emirates also support a few hundred more. These are grazers which feed principally on the shallow beds of seagrasses. The Gulf’s dolphins and whales are equally vulnerable. Schools of scores of dolphins are common in the Gulf. A few baleen whales, probably Bryde’s whales, have also been recorded.

Green turtles and hawksbill turtles live and breed in the Gulf, particularly on the Saudi Arabian islands and possibly others in the Hawar archipelago of Bahrain, and on islands belonging to Iran and the United Arab Emirates. Loggerheads may also be seen. Turtles are particularly vulnerable to oil. Not only do they become fouled, but their nesting beaches in which they excavate pits for laying eggs are easily contaminated too. In the case of the Saudi Islands, this risk is considerable.

The Gulf supports extremely large populations of sea snakes from 9 or 10 species, all of which are air breathing animals. One is a pelagic feeder and the remainder are bottom feeders; though all are carnivores that prey mainly on fish. Their role in the Gulf ecosystem has hardly been studied. Sea snakes may not raise public concern or interest as much as the turtles, but ecologically they are likely to be at least as important.

Finally there are the seabirds, whose oiled images first brought home to many the realisation of the magnitude of the oil spills. The spring migration starting this month will bring an estimated 2 million birds to the mud flats of the Arabian Gulf shore for feeding and recuperation. These birds risk direct contamination.