Testimonials
Hello

USA Travelers: "This is an awesome experience"

1
- 18
Trip Advisor
TripAdvisor
1194 reviews of Memphis Tours Egypt in Cairo
Memphis Tours Egypt
© 2012 TripAdvisor LLC
powered by TripAdvisor

Marine biology of Sinai

Coming from al-Tur we had just crossed the hot southern Qaa Plain. At a sharp left curve we left the road to continue our journey on a sandy track. After about fifteen kilometers a military post let us pass as we showed the necessary permission from the police station in al-Tur. We had arrived at Ras Muhammad, the southern tip of Sinai. Now the track split into several branches and we followed one of these across a rough, fissured, and bleak limestone plain until our way suddenly ended at a little bay. Before us lay the deep blue water of the Red Sea. Equipped with diving mask and snorkel, we swam over the reef shelf. The first coral and fish appeared before us and the underwater landscape became more and more impressive. Suddenly our breath was taken away: through clouds of innumerable multicolored fish we could look between stunning corals straight down to the seemingly endless blue depths of the sea. For one brief moment we thought we were falling, but then our attention was caught once again by the unbelievable variety of colors and forms in the reef of Ras Muhammad.

It is hard to imagine more disparate biospheres than the gray and desolate limestone desert of Ras Muhammad and the coral reef of the Red Sea almost exploding with life and color. Complete strangers, leaving the water after their first dive, have come to us and as though under duress simply burst out with their experiences and impressions.

Although we have seen many other very beautiful coral reefs, we agree with the opinion of numerous experienced divers that Ras Muhammad is one of the best diving sites in the world. Yet according to normal standards, there should not be any coral reef here at all.
Like every living thing, coral makes certain demands on its environment, and if one single condition is not met, it cannot survive. These conditions include warm, clear, sun-flooded, and nutrient-poor sea water, with a temperature of not less than 18-20? centigrade even in the cold season, and a hard floor where the coral can attach itself firmly. The nutrient-poor factor seems strange at first, but is understandable in light of the fact that highly nutritious waters are generally cloudy. For corals it is most important that the sunlight penetrates deep into the water.

The conditions for coral are fulfilled in a belt of varying width around the equator, especially on the eastern coasts of the continents. Due to the earth's rotation the warm water on the sea's surface normally flows westward and therefore strikes the eastern coasts.

So it is rather astonishing that the Red Sea meets these environmental conditions; it is after all a small sea located quite far north. The artful interplay of geological and geographical factors is responsible. The deep rift system has split the old basement complex in the Red Sea, as well as in the Gulf of Aqaba, the miniature version of the Red Sea, thereby creating the hard bottom surface for corals. Due to its location in the Afro-Asian desert belt there is little fertile land around or freshwater inflow, so no nutrients are washed into the sea to cloud the water. The hot desert climate heats up the water sufficiently in the summer.
On cold, clear, winter nights, the thermal radiation into space is so high that the water should in theory cool down too much. But even here, the combination of geological circumstances and climatic factors is helpful: the Red Sea and the Gulf of Aqaba he on a north-south axis. Their southern ends are both nearly closed by straits, the Bab al-Mandab and the Straits of Tiran. Moreover, there is a high rise in the sea floor at both straits. The north winds that predominate in the region push the surface water, which becomes very warm in the summer, to the south all year round. In the straits it meets the high sea floor and to a large extent is forced downward. Thus even at a depth of one thousand meters the water can be an unusually high 20? centigrade. In the depths, the water is gradually pushed to the north, where it finally comes to the surface. In this manner the water circulates, supplying sufficiently warm water year-round-in winter the cold surface water is carried to the south and down toward the bottom and is replaced by warm deep water in the north. No coral sea can develop in the shallow Gulf of Suez, since such water circulation is impossible and since disturbed sand constantly covers the coral.

The coral builders of the reefs are unusual creatures in several respects. Being Coelenterata, they belong to the most primitive of multicelled animals, but with their tentacles and stinging cells they control the most complex cells to be found in the animal kingdom. Due to their stationary way of life and their simple structure, corals were for a long time thought to be plants. The single, usually microscopically small polyp consists of a sack-like body enclosed by a wall consisting of an exterior and an interior cell layer with a relatively thick gelatinous supporting lamella in between. Serving as both mouth and excretory organ, the only orifice of the body lies at the upper end, inside a ring of six or eight movable tentacles. The entire exterior wall and the tentacles are covered by stinging cells for catching tiny plankton organisms.

An individual polyp reproduces asexually through budding. Since the young polyp remains attached to the parent polyp through a connective tissue throughout its life, over the years a large colony of polyps is formed, which together create a coral skeleton. To do this, however, the ability to produce limestone is also necessary. The ability to synthesize limestone really is an outstanding achievement as it enables the polyps not only to build calcareous cups to which they can retract in time of danger but also creates the foundation for the genesis of one of the most multi-faceted and species-rich living communities in the world. Coral reefs are the largest natural structures that exist. The Great Barrier Reef alone, along the eastern coast of Australia, is over two thousand kilometers long; and in the course of the earth's history fossil coral reefs have been folded upward to become mountains.

The limestone excretion of polyp colonies is a biologically very interesting process that was first investigated in the late 1950s and early 1960s by the German-American scientist Goreau. What distinguished his research was his observation that coral polyps live in symbiosis with single-celled algae, the Zooxanthellae. These algae are responsible for the colorfulness of many corals. Their real importance, however, lies in their use of the carbonic acid formed during limestone production for photosynthesis. If die carbonic acid were not immediately removed, it would dissolve die newly formed limestone. This is why limestone formation takes place only in tie daytime, when the algae produce their nutrients through photosynthesis with the help of sunlight. And it is also the reason that coral reefs can only grow in clear, sunlit water.
The growth rate of a coral is difficult to express in numbers. Young corals grow faster than old ones; branched types grow faster than compact types. The temperature also plays a role: optimal growth takes place at a temperature of about 25-27? centigrade. Generally, the growth rate amounts to only a few centimeters per year, so every piece of coral broken is a loss. Reef damage occurs when too many divers and snorkelers touch corals, trample them, or break them off.
The effects of the symbiosis between polyps and algae extend much further. As a waste product of photosynthesis the algae produce large amounts of oxygen, which the whole reef community needs to breathe. Since the oxygen is emitted in a fine form, the sea water is supersaturated to well above 100 percent. This is one of the reasons why coral fish and other reef organisms cannot be kept in an aquarium without difficulty, since they are accustomed to an unusually high oxygen concentration.
Now it is may be understood why the lack of nutrients in the sea water is not a problem for the maintainence of the gigantic reef community. The symbiotic algae produce many more nutrients by photosynthesis than they can use and, with the surplus, feed the polyps. The polyps, for their part, filter particular compounds out of the sea water that the algae need to live. So has arisen a true symbiosis, a genuine partnership based on mutual dependence and assistance.
Not all corals are able to create limestone, mainly just the Hexacorallia (six-tentacled species). The Octocorallia, with eight tentacles, are among the most beautifully colored and variously formed soft corals, but not among the reef-creating species. Like other stationary species of sponges, lime-corals, or mussels, they compete for space and, by spreading too much; they may even inhibit the growth of stone corals. Under good growing conditions, stone corals build a real labyrinth of holes, tunnels, channels and grottos of every size, which offer other organisms of very different species countless hiding places and homes. This is one of the most important requirements for a particularly species-rich community, since a highly diverse range of organisms find their ecological niches.

In addition to asexual reproduction through budding from the body wall, coral polyps also reproduce sexually. Depending on the species, polyps can exist as separate sexes or hermaphrodites. In each case, they produce sex cells in their interior cell layer that are deposited in the stomach hole. Sperm are expelled in masses by all polyps at certain times and are filtered from the sea water by polyps of the same species and transported to the stomach. The sperm fertilize the polyps' egg cells and within a few days tiny, free-swimming planula have developed. Remarkably, the egg cells of the mother polyp transfer to the larvae some of the symbiotic algae that are essential later for building new corals. The larvae are expelled simultaneously by all polyps of a coral or a species, and in such amounts that milky clouds can form over whole reef walls.

The larvae augment the plankton and are in large part eaten by plankton-eaters such as the manta ray, which can grow to seven meters broad. Only the few larvae that survive and a good surface to attach to can transform themselves into polyps. This tiny, lonely polyp begins with limestone excretion and asexual budding and builds a new coral in the course of time.
Sexual reproduction through larvae helps corals to spread, which explains how these animals came from the Indian Ocean to the rift system of the Red Sea, which emerged later.
There are different reef types, which vary in their construction. In the Red Sea, as well as in the Gulf of Aqaba, there are mainly fringing reefs extending from the coasts. This is because the narrow but deep rift provides the shoreline with a hard bottom and sunlit water. The corals grew from here into the open sea and developed the present structure of fringing reef. Close to the beach, the reef top consisting of dead coral limestone is covered by only a few centimeters of water and at ebb tide 1 exposed. Further out to sea the first stunted corals can be seen arduously eking out an existence. Behind these, the corals become more numerous and better developed as the reef crown is approached.

Here, at the front edge of the reef, with abundant light and waves, the corals have the 1 growing conditions. In many places, the reef crown extends forward into the open sea over the steep reef wall. The reef walls are covered, especially in the upper parts, with flourishing corals, and even downward the coral growth in the Red Sea diminishes very slowly, a consequence of the clear water. It has been ascertained that the photosynthesis of the symbiotic Zooxanthellae still functions at a depth of fifty meters and in extreme cases even at a depth of ninety meters.

When the reef wall does not immediately fall steeply to great depths but forms gentle slopes or terraced steps, wonderful coral towers can grow to several meters high, reaching sometimes almost to the water surface. On broad reef tops, sunken areas on the coastal side of the reef crown create lagoons where corals grow as well. Since the lagoon is not very deep and usually does not get enough fresh water from the sea through channels in the reef crown, and furthermore since the ground is covered with sand, the living conditions for corals are definitely less favorable here than at the reef crown.
Coral reefs constitute one of the most species-rich communities on earth. Only tropical rainforests and steppes or savannas (such as those in East Africa) are comparable.
Corals are the basic food for numerous animals like the well-known parrot fish, the infamous crown of thorns, and many multicolored nudibranchs and flat worms. The latter not only eat the coral. They do not digest the poisonous stinging cells but deposit them in their skin, creating an effective defensive weapon against predators. Bright red, black, and blue sponges bore their way into the coral, as do mussels or bristle worms with their patterned tentacle crowns.
Many stationary animals compete with the stone coral for space: the beautiful soft corals as well as other species of Coelenterata like the fire coral and sea anemones. The latter live in a very special symbiosis: anemone fish of the genus Amphiprion swim without danger between their stinging tentacles because they develop a protective substance in their skin as a result of their constant contact with the sea anemones. They defend 'their' anemone with vehemence and are not afraid of the much bigger divers. The symbiosis between the cleaner wrasse or the cleaner shrimp and their customers, including sometimes even dangerous predators like barracudas. is also well known. The little blue-, white-, and black-striped fish swims unconcerned in the toothy mouth of a two-meter-long barracuda. Even a diver may have the honour of getting his arms cleaned if he does not move.
Besides the many species of animals, from almost all branches of the animal kingdom, that are bound fast to the coral reef, there are countless other creatures that, although also found in other places, prefer to live in the reef. In die course of millions of years a network of numerous interwoven relationships among different species has developed in the coral reef and there-by created a habitat so rich in nutrients that even fish from the open sea such harks and barracudas come to find their prey. The primeval sea turtle can be seen searching for food, and it is a unique experience to be circled by a huge manta ray, which shows little fear.

This complex ecosystem cannot be described even close to completely. Every single time in our more than one hundred diving and snorkeling trips we discovered at least one lifeform we had not previously known - the coral reef will offer work for generations of scientists. Nevertheless, we want still to address some interesting and frequently discussed aspects.

The dangers of the reef are much discussed, especially among newcomers in Sinai. Some have to overcome considerable fear when entering the water with diving mask and snorkel for the first time at Sharm al-Sheikh or Ras Muhammad. They are primarily afraid of sharks, of which several species do exist in the Red Sea. The vantage rock of Ras Muhammad bears the name Shark Point with reason, as, at least a few years ago, sharks could frequently be observed there. In the Red Sea, the fear of sharks is quite unfounded if the diver observes certain rules and does not provoke them. Sharks are usually shy predators that flee from humans, which is why these magnificent predators are scarcely to be found nowadays at much-frequented reefs and diving places like Shark Point. Naturally, sharks are provoked by divers or snorklers carrying dead fish with them, but fishing is in any case prohibited in the reef areas of Egypt. The fish-blood in the water lures the nearby sharks without fail and may provoke in them a real rapacity. That accidents can happen under these circumstances is obvious and fishing divers have only themselves to blame. Furthermore, it is not very sensible to pull at the tail fins of sleeping nurse sharks or whitetip reef sharks. Although these animals are only 1.5 meters long they can be very dangerous in such situations. It is also dangerous to swim too far into the open sea, and harbor areas and ship routes especially should be avoided, because here sharks are used to eating ships' refuse on the surface of the water. A wriggling swimmer in such an area is an incitement for sharks. The only two accidents with sharks which we have heard of in the northern Red Sea happened under exactly such circumstances. A soldier, who wanted to swim from Sinai to the Island of Tiran, was attacked by a mako shark in the area of the shipping lane. The same happened to a couple swimming next to a ship in the harbour of Eilat.
Divers and snorklers who stay calm in the water normally need not fear sharks. Instead they can be glad if they once get the rare opportunity to observe a slim reef shark, a ray-like angel shark, the strange hammerhead, or one of the various gray reef sharks.
Build Your Trip