NATURAL WONDERS
Top picks off our coats – and past issues of Oman Today

We've been looking at the sultanate’s natural wonders for more than a quarter century now, and much of it has been over, and under, our seas. As part of our focus on the ocean this issue, here are excerpts from the recent past about marine life:

Between the grains
December 2004

The formation and movement of particles on a beach is slightly different and affected by a few more processes than in the desert – such as waves, tides, offshore currents and long-shore drift, all of which move and erode particles in different ways. The effectiveness of each mechanism on a beach depends on its energy, so each will erode and deposit sediment in a different manner and location. Wave action can sort beach material so that shingle will accumulate as a ridge high up on the beach, while sand may only be exposed at low tide. Or long-shore drift may carry sand to one end, leaving shingle at the other. In Oman most of the lighter and whiter sandy beaches are composed of minerals such as calcium carbonate. The sand on these beaches is known as calcerous sand and is mainly composed of debris, shells and skeletons from marine organisms. When they die, decompose and break down, they become part of the beach. You may notice that many of these beaches have coral reefs, parts of which break off, erode and form a significant source of sand. The sultanate also sits on a lot of limestone, which itself is composed of previous layers of seabed (and hence more dead marine organisms). The erosion of this stone also gives beaches their lighter colour. The darker coloured beaches of the Batinah coast consist mainly of eroded rock containing darker mineral components from the ophiolite rock. Very few corals exist on this part of Oman's coast but there is still plenty of rock to erode.

Stargazing turtles
January 2005

To hatchling turtles emerging from a nest at Ras al Hadd, the night sky may be their first glimpse of the world. The pattern of stars that they see may be permanently imprinted on their minds, allowing them not only to navigate across oceans in search of food as they grow, but also to return as adults to the exact same beach on which they themselves hatched some 20 to 50 years previously. In using the stars to navigate, turtles learn to associate the position of stellar constellations with the time of night and with a specific geographic direction. Then they have to compensate for the changing direction of the constellations during the night. So accurate is turtle navigation, however, that individuals are thought to nest often within metres of their birthplace. To achieve this, other more finely tuned senses, perhaps picking up chemical cues, must take over at some stage near to the beach.

Sleeping dolphins
March 2005

Like humans, most animals, from ants to elephants, need sleep to function effectively. Some sleep for a matter of minutes, whilst others sleep for up to 20 hours every day. When animals sleep depends largely on when they need to be awake. Predator avoidance is one factor that helps to determine the best time to be out and about, as is the need to hunt.

Dolphins are able to sleep for short periods whilst in motion. They may enter a sort of autopilot mode, sleeping whilst continuing to swim, and rising periodically to breathe at the surface. In such cases, the presence of the rest of the group provides a feeling of safety from predators. Like humans, their brains are divided into two hemispheres. These animals have the ability to allow one hemisphere of the brain to sleep while the other half is awake. During sleep, dolphins tested in an aquarium swam mechanically in circles and observation of wild dolphins has shown much the same behaviour. Spinner dolphins, for example, are known to enter shallow waters of protected bays to sleep. These bays are often characterised by white, sandy seabed where the dark shape of a predator such as a shark is more clearly visible. The dolphins swim in circles, presumably with one half of the brain resting, whilst the other half keeps an eye open for danger. What is interesting, and has been shown to occur in birds, is that moving in clockwise followed by anti-clockwise directions allows the animals to alternate which halves of their brains are getting rest – the outward facing side remaining alert to predators whilst the inward facing side sleeps.

Deadly cuttlefish
April 2005

Cuttlefish are stealth hunters of the seas, camouflaging themselves on the seabed and using their tentacles to lure prey to within easy reach. The long tentacles, equipped with suckers at their tips, then shoot out and seize the prey, normally a hapless crab or shrimp. At the centre of the arms, on the underside of the head, is the lipped ring of the mouth, within which is a sharp, horny beak that the cuttlefish uses to rip and shred its prey, swallowing the smaller pieces of flesh. In hunting, cuttlefish are greatly aided by well-developed eyes, which are more similar to those of fish than those of other invertebrates. They are also among the most intelligent of all invertebrates and so can literally outsmart their prey. The time at which a cuttlefish hunts has partly been decided for it, over evolutionary time, by the intriguing design of the internal shell. One of the functions of the shell is to provide buoyancy. Its chalky, porous centre is filled with gas (mostly nitrogen) and liquid. The relative amount of liquid present determines the buoyancy; a high proportion of liquid makes the shell denser. But the amount of liquid and gas, it has been discovered, is controlled by the amount of ambient light. During daylight, more liquid is pumped into the shell and the cuttlefish stays mostly on the seabed. At night a larger proportion of gas increases buoyancy and the cuttlefish can more actively hunt. For both capture of prey and especially for escaping predators, cuttlefish have yet another impressive skill at their disposal: despite their often ungainly appearance, they are champion swimmers. One way in which they swim is to send undulations along the fin around the mantel margin. But when they need speed and agility to escape a predator, they switch to jet propulsion, which can propel some of the faster cephalopods at burst speeds of up to 40kmph.

Regenerating starfish
May 2005

Virtually a symbol of sea life, the starfish is one of the most familiar of marine invertebrates. A whole host of different kinds live in Omani seas, in shallow rock pools, on soft sandy seabed, amongst stony corals and all the way down to the deep ocean floor. They come in virtually any mix of colours, but their shape, however, is unmistakably uniform and fitting to the name. It is this shape, as well as a few other features, that set the starfish apart from all other animals. Starfish are also able to regenerate themselves in the event that they are injured. A lost arm is easily regrown, but starfish can do better than that. They can also regrow their bodies if they have enough of the central disc remaining after an injury. As little as one fifth of the central disc attached to an arm is sufficient for some starfish to regrow the rest and four new arms. Some sea cucumbers may even throw out their internal organs, possibly as a defence mechanism to deflect would-be predators or help eliminate waste that builds up after a period of heavy feeding. They then re-grow fresh, fully functional organs from the stubs left in the body where the ejected organs broke off. Scientists have suggested that such phenomenal wonders of nature should be studied for their application to human medical science. Although spontaneous re-growth of organs in humans is surely a distant dream, chemical compounds found in some echinoderms have been shown to have properties of interest in pharmaceutical research.

Venom under water
June 2005

That we are unlikely to encounter sea snakes often is reassuring, as their greatest weapon is venom. They are among the most venomous of the world's snakes and a bite can be fatal to humans. However, venom probably evolved in a feeding context rather than for defence, and must be powerful enough to rapidly overcome prey such as fish, crabs and squid, while also actively aiding digestion. The fixed, tubular fangs of such snakes are just a few millimetres in length and hang from the upper jaw at the front of the mouth.

Although inquisitive, sea snakes generally lack aggression and are unlikely to bite. Their heads are also narrow and small, allowing them to enter the burrows of shrimp, eels and other fishes on which they feed, but limiting the gape of their mouths and so restricting their ability to bite something as large as a human limb. Most bites apparently occur on the fingers of fishermen who inadvertently catch sea snakes in their fishing nets. Fortunately, this is a rare event.

Ghostly cleaners
July 2005

One of the main beach scavengers in Oman is the ghost crab. It patrols the beaches from dusk till dawn and is often most active in the dark of night, possibly lending cause for its common name. In the sultanate, however, ghost crabs are very commonly seen in daylight hours as well. Its scientific name, Ocypode, means 'swift-footed.' Measuring only a few centimetres across, with stalked eyes that give them a surprised look, ghost crabs can be quite appealing. It is their role as beach scavengers, however, that should really endear them to us. They will consume almost anything organic that the waves wash up or the wadis wash down. The main reason for this is that they are opportunist feeders. The beach typically has only a limited range of food available, so anything new that comes along is a welcome treat. Given time, ghost crabs will ensure that every last scrap of food delivered to them is devoured, even scooping sand into their mouths and separating out the microscopic food particles from the grains of sand. So next time you head to the beach, spare a thought for a little crab. See him not as a scuttling, creepy-crawly armed with fear-provoking pincers, but as beach custodian, helping to keep our coast clean.

Coloured reef fish
September 2005

Like the coral reefs around which they live, reef fish come in an incredible array of colours, shapes and sizes, each adapted to a particular niche in a highly varied ecosystem. Some of them live their entire lives within the confines of a few coral colonies, among which they are well hidden and away from which they rarely dare venture. Most of these are well camouflaged; their colour, form and even their shape may take on that of their surroundings. Others may actively display their vibrant colours for all to see, presumably providing signals to others of their kind, perhaps relaying the message to predators that they are poisonous, or to others of their species that they are a fit mate. The colour patterns of the adult and juvenile emperor angelfish (Pomacanthus imperator) are both striking and strikingly different. This once led scientists to mislabel them as separate species. It is now well known that many fish show such differences between adult and juvenile stages. The reason probably lies partly with a need to remain camouflaged, particularly as a young fish and partly to do with the complex social and territorial mechanisms that are associated with reproduction. Juvenile fish, for example, may pose less of a threat to a territorial adult that might otherwise threaten the survival of the juvenile long before it has had a chance to grow up and reproduce.

The history of pearls
January 2006

Few people strolling along the beach at Azaiba after spring tides notice the higher dunes in places that expose layers of shells up to a metre thick. Closer investigation will reveal that most of the contents are oyster shells, often still glowing with their characteristic iridescent pearly inner coating. 800 years ago, Seeb was best known as a pearling centre famous for exporting its precious products to India. Muscat was the main centre of the trade from the 18th century to the 1920s with other Gulf ports. So what happened to the legendary pearls of Oman? In the heyday of pearling, Oman supplied a third of the fleet and provided work for thousands of boat builders, divers and sailors. Every year in May, at the height of summer, the big sambuqs unfurled their sails and set off from Kuwait, Bahrain, Qatar, Dubai, Ras al Khaymah and the Batinah coast of Oman. Their crews could expect to be away at sea for the next five months, until conditions changed with the approach of autumn in September, making diving unprofitable and unsafe as the water clouded and got colder. Almost half a year of the most humid and hot months at sea, generally over the Great Pearl Bank off Abu Dhabi, all to hunt the depths for their prey: the two species of oyster most likely to harbour the odd gem-quality pearl, Pinctada margaritifera and Pinctada radiata.

Beachcombing
June 2006

Oman's 1,300km of beaches offer a ready opportunity to indulge in one of our earliest ancestors' favourite activities - beachcombing. The Gulf is home to at least 1,200 species of mollusc, the term given to the huge family we usually just call snails or shellfish. Some are found on land but most live in watery habitats, both fresh and salty. The vast majority of molluscs have an external skeleton or shell protecting the soft and often juicily edible body. There are 80,000 to 10,0000 species worldwide, divided into six classes, but the two producing 'shells' as we know them are the gastropods (univalves) and bivalves. These are also the most widespread, attractive, varied and collectible. So what makes the shell itself so remarkable and attractive? The soft body of a mollusc, its mantle, can often extend to cover the entire shell. It extracts calcium carbonate, or 'lime' from seawater and deposits it around itself. Lime bonds with conchiolin, a natural substance similar to our nails, which the creature secretes. As the shell grows, the mollusc covers more of its outer surface with more layers, writing its own genetic signature into the surface in a programmed pattern of colours, lines and textures. It also cleverly makes more room inside for its growing soft body by dissolving some of the inner layer and re-depositing it externally. Oysters and mussels line their shells with satiny iridescent layers of nacre, or mother-of-pearl, which may produce a natural pearl.

In Oman, you need a license to collect live shellfish. Carefully replace any rocks you've lifted after checking what's under them. Inspect any apparently empty shells for signs of life – you might be abducting a hermit crab, which has prior right of occupation. Wash the shells to flush out any remaining dead contents, or the smell will soon notify you. Once dry, you can buff them up with a little olive oil if they look dull. If you become a serious collector, you'll have to keep them away from light, as they will fade in time.