Research by marine biologists from Wageningen University has shown that feeding on zooplankton by scleractinian corals has been greatly underestimated.
|The reefs of Marsa Alam - paradise lost?|
|Written by Tim Wijgerde|
The Red Sea truly is an underwater paradise. This seawater inlet of the Indian Ocean harbours a myriad of colourful fish and invertebrate species. An interesting area along the Red Sea coast is the Marsa Alam region, which still hides pristine coral reefs. Unfortunately, this area is also experiencing an increasing number of tourists each year, which has already impacted local wildlife. As coastal development remains a major local activity, the future of the Marsa Alam reefs is uncertain.
A school of Chromis viridis swims close to an Acropora colony, and rapidly retreats into the coral when faced with possible danger.
The Red Sea has been known for its underwater splendour for many years, and has been a popular diving attraction for decades. This relatively small water mass harbours many endemic species, including corals and fish. The origin of the name Red Sea possibly stems from the red mountains which line the coast. An alternative theory refers to a species of cyanobacterium, Trichodesmium erythraeum, which gives the Red Sea a reddish haze during blooms.
The Red Sea is mainly visited from Egypt, which has a flourishing tourism industry. Well-known destinations are Sharm el-Sheikh, situated in the Sinai peninsula, and Hurghada, located in the northern area of the Red Sea. The Sinai peninsula is flanked by two water bodies, which split from the Red Sea close to Hurghada - the Gulf of Suez to the left and the Gulf of Aqaba to the right. Along the Gulf of Aqaba coastline lie small towns famous amongst divers, such as Dahab and Taba.
The negative effects of human presence are clearly visible in larger cities such as Sharm el-Sheikh and Hurghada, where coral reefs have been severely impacted by coastal development. Hotels situated directly along the coast all have their own "house reef", a popular concept amongst tourists. Although most hotel reefs still harbour healthy fish, corals and other invertebrates, damages are evident. Further out the coast, remote reefs and islands can be found which still are more or less pristine. In the southern areas of the Red Sea, anthropogenic impacts fortunately are less severe due to limited tourism activity. This is because tourism here is still on the rise. Other factors are of a social-political nature, as several countries along the Red Sea including Sudan, Eritrea, Somalia and Saudi-Arabia still experience conditions unfavourable to tourism. Egypt and Israel on the other hand have been stable for a long period, and now have well-developed areas of (eco)tourism. A new region where ecotourism is on the rise is Marsa Alam, named after a small town in the southeast of Egypt.
A new Hurghada
Marsa Alam has developed a very good reputation amongst the worldwide diving community due to its pristine reefs and relative abundance of sharks, dolphins and sea turtles. Mangrove forests can also be found in this area. Marsa Alam itself is a small town which is currently in strong development. In 2003 the Marsa Alam International Airport was opened, located approximately 65 km (41 miles) north of the town of Marsa Alam. The airport has catalysed the development of new hotel areas, which is reflected by the local landscape today. New hotels are under construction everywhere. Some fear that this area may become a new Hurghada within several years, which could be detrimental to local wildlife.
Large groupers such as Epinephelus tauvina dwell in the lagoons of Marsa Alam.
The coral reefs along Marsa Alam are mainly fringing reefs located very close to the shore. The lagoons, small water bodies which are protected from the sea by the coral reef, are quite narrow as a result of this. The hotels in this area also have their own reef sections which can be visited directly from the beach. In general, these reefs are not managed well, which has resulted in the destruction of many lagoons. Although hotel guests are instructed by hotel personnel, they often damage corals and clams, stir up the sand causing sedimentation and feed the local fish in order to take pretty pictures. Positive developments are piers which allow visitors to traverse the reef safely, and coloured flags which indicate weather safety. Where the reef crests and slopes down towards the sand bottom, coral damage is significantly less prominent.
In the lagoons of Marsa Alam, biodiversity is still quite high despite heavy damages. Several fish species can be found here, including butterfly fish (Chaetodon semilarvatus, C. fasciatus), surgeonfishes such as Zebrasoma desjardini, wrasses (Thalassoma klunzingeri), damsels such as Indo-Pacific sergeants (Abudefduf vaigensis) and goatfishes (Parupeneus forsskali) which constantly stir up the sand. Groupers (Epinephelus tauvina), Blue and Picasso triggerfish (Pseudobalistes fuscus, Rhinecanthus assasi) and pufferfish (Arothron diadematus) also dwell here. Every now and them, a lost stingray can be encountered (Taeniura lymma). Clownfishes (Amphiprion bicinctus) are found in various anemone species such as Entacmaea quadricolor, Heteractis magnifica and H. crispa.
A pair of butterfly fish, Chaetodon semilarvatus. This species lives a secluded existence and can often be found in caves and underneath coral overhangs.
A pair of Amphiprion bicinctus anemone fish in their host, Heteractis crispa. The male (top right) is significantly smaller. The larger, dominant female repels any intruders.
The dominant corals in the lagoon are Stylophora pistillata, various Porites sp. and Hydrozoan fire corals such as yellow Millepora dichotoma and green M. platyphylla. Sea urchins such as Diadema setosum are also abundant. Algae cover is quite minimal, except where Dascyllus marginatus damsels have their territories. This is possibly due to limited algal grazing by surgeonfishes, which are not allowed to venture here.
Video: This specimen was tentatively identified as Dascyllus marginatus. It is actively defending its territory by attacking the camera. Wild animals are better left alone, therefore keeping some distance is recommended.
On the outer reef slope, the reefs seem to be in much better condition. Due to the depth of the reef, which is roughly between 2 and 20 meters (7 to 67 feet), most corals look healthy. The usual trampling of "colourful rocks" fortunately is very uncommon here. The biodiversity on the reef slope is remarkably higher, with dozens of coral and fish species. Colourful Pocillopora colonies, such as P. verrucosa, P. meandrina and the well-known P. damicornis, ornament the reef. These species can be found in purple, pink and beige colours. Porites spp. form a striking yellow contrast with these abundant corals.
Millepora platyphylla, a member of the Hydrozoa class, also known as Fire coral. Due to its colony shape and colour, this species is easily misidentified as a Montipora sp.
Most colonies on the reef slopes are fairly small. Apparently, local conditions limit growth of most species. These can be biotic, such as coral predation by fish, or abiotic such as high temperatures which promote bleaching and mechanical damage caused by storms and wave action. Exceptions are certain Porites species, which have grown to impressive sizes of over 1.5 m (5 ft) in diameter.
Upon close inspection of the reef, many cryptic species can be found. Porites colonies often contain colourful Spirobranchus giganteus polychaetes, often referred to as Christmas worms. This name stems from the tree-like feathers on top of the worm's scolex, or head. These structures are used for capturing plankton from the water, as well as for gas exchange. When a predator or human ventures too close to these worms, they quickly withdraw their feathers into their tubes after which the operculum closes its entrance.
Other corals such as Stylophora pistillata and various Acropora and Pocillopora spp. often house small symbiotic crabs from the genus Trapezia, such as T. cymodoce. These small crabs live off the coral's tissue and mucus, and also consume detritus captured by the coral's branches. According to recent scientific findings, a pair of these crabs may devour up to 130 cm2 of tissue per month! This symbiosis between coral and crab is often regarded as commensalism or even parasitism, however it seems that the coral actually benefits from this interaction. The grazing of coral tissue by the crabs stimulates the production of coral mucus, which facilitates the process of removing detritus and fouling organisms which could otherwise suffocate the colony. Colonies which have lost their symbiotic crabs have found to display higher rates of mortality. Trapezia crabs also protect their hosts against corallivore echinoderms such as the Crown-of-Thorns starfish (Acanthaster planci), which is able to consume large areas of coral within a short time. Unfortunately, many corals which are traded in the aquarium industry have lost these highly interesting creatures.
A Spirobranchus giganteus hides in a Porites colony. The yellow feathery structures on top of the worm are used for breathing and filtering plankton from the water.
Pocillopora verrucosa with a symbiotic Trapezia crab. Corals do not only live in symbiosis with algae ( zooxanthellae) and bacteria, but also with animals such as crabs.
Fish also form symbiotic relationships with other species, and this is no different on the reefs of Marsa Alam. The Giant Moray (Gymnothorax javanicus) can be found here living together with Stenopus hispidus shrimp. The shrimp keep the moray free of ectoparasites, whilst they find refuge inside the eel's burrow. This symbiosis is a nice example of mutualism.
A pair of Stenopus hispidus shrimp inside a Moray's lair. The Moray provides the shrimp with refuge and nutrition.
Fishes which inhabit the reef in large numbers are Anthias spp., Chromis dimidiata, surgeonfishes, angelfishes and butterflyfishes. Butterflyfishes such as Chaetodon fasciatus and C. paucifasciatus traverse the reef whilst nipping on coral polyps, often in pairs. Hawkfishes, including Paracirrhites forsteri and Oxycirrhites typus can also be found, and rapidly retreat whenever a diver ventures too close.
A hawkfish (Paracirrhites forsteri) resting on top a coral, possibly a Porites sp. These corals resemble the purple Hydrozoan Distichopora violacea, however this last species is usually found in deeper waters and neither displays flower-like polyps nor harbours zooxanthellae.
Underneath the reef surface, in the numerous small caverns, many more cryptic species lurk. Colourful sponges, shrimp, crabs, brittle stars and sea urchins dwell here. Young fish also hide from predators in crevices and caves, both on the outer reef and in the lagoons. Artificial burrows also seem satisfactory to marine life; small plastic bags are sometimes inhabited by numerous young fish.
A coral reef is a dynamic ecosystem, and looks different during various times of the day. During sunset, the fluorescent properties of coral pigments become visible and certain fish become more active. Lionfish such as Pterois sp. and Giant Morays (G. javanicus) slowly appear. Brittle stars creep out of the reef's crevices in huge numbers, and give the lagoon into a gloomy blackness. During the day, Snowflake Morays (Echidna nebulosa) and pipefish (Corythoichthys schultzi) seem to be more active.
Snowflake Morays (Echidna nebulosa) are commonplace in the lagoons around Marsa Alam.
The Ras Qulaan Islands
The coast of Marsa Alam is littered with small islands and remote coral reefs, similar to the Sharm el-Sheikh region. Popular reefs in the area are Elphinstone and Dolphin reef. A key hotspot of biodiversity are the Ras Qulaan Islands. Sometimes referred to as the Virgin Islands, they form a major part of the Wadi el Gimal National Park. The islands are subject to strict environmental protection similar to the well-known Ras Mohammed National Park near Sharm el-Sheikh. This is very fortunate, as there is much to be protected. For example, the islands are nesting grounds of the famous Osprey or Sea hawk (Pandion haliaetus).
A pair of inquisitive Chaetodon paucifasciatus, feeding off coral polyps.
The Ras Qulaan Islands can be visited by boat, which is a 45 minute trip from the Hamata harbour. Although no people are allowed to step onto land, tourists may dive and snorkel around the reefs which line the islands. The average depth of the surrounding water is very shallow, between 0 and 20 meters (67 feet).
The reefs surrounding the island are still quite pristine, with Acropora colonies of several meters in diameter. High biodiversity ensures that much is to be seen, including large stands of Heteractis magnifica anemones inhabited by groups of A. bicinctus. On occasion, groups of young Dascyllus trimaculatus damselfish coinhabit the same anemone. Black corals such as Antipathes and Cirrhipathes spp. can also be found here. Large barrel-shaped macro sponges grow in shaded areas, and are teeming with small schools of fish such as Chromis dimidiata.
A brown barrel-shaped macro sponge is surrounded by a small school of Chromis dimidiata. On the left, a pipefish (Corythoichtys schultzi) can be seen, lying on a small Porites coral.
Sharks, dolphins, sea turtles and even dugongs (Dugong dugon) are regularly found near the islands. Mangrove trees also grow in the area, and their roots hide juvenile reef fish. These patches of mangrove trees form a unique ecosystem, which is closely connected to the coral reefs as they supply the reef with new generations of coral fish.
A black coral (Cirrhipathes sp., tentatively identified as C. anguina or C. contorta) grows near the edge of a cave. Black coral polyps cannot retract themselves when faced with danger. Although they resemble gorgonians, these corals are actually more closely related to stony corals.
A visit to the Marsa Alam region certainly is worthwhile, especially because of the healthy reefs and peaceful environment. Your visit will however sustain tourism activities which threaten this delicate wildlife area. Within a decade, this region will certainly have transformed into a large-scale tourist destination. One can only hope that the Egyptian government will establish more stringent ecomanagement practices, so that these reefs will continue to flourish. Even without pollution, poor ecosystem management and coastal development, global warming and ocean acidification will continue to threaten these unique ecosystems.
The coastal areas of Marsa Alam are often examples of poor ecosystem management. Many lagoons are heavily damaged due to tourist activity. Remains of trampled marine life, such as Tridacna clams, are used as ashtrays.
Video: Amphiprion bicinctus anemone fish together with Dascyllus trimaculatus damsels. Together, they occupy a large Heteractis magnifica sea anemone. Note the numerous offspring of D. trimaculatus. This video was shot at one of the Ras Qulaan Islands.
All photographs and other media by the author. The author wishes to thank Jorick Hameter for supplying camera equipment.
Rinkevich, B., Z. Wolodarsky and Y. Loya, 1991. Coral-crab association: a compact domain of a multilevel trophic system. Hydrobiologia 216/217:279-284