Survey of Yemen’s Red Sea Coral Reefs: UNTAPPED TOURIST ATTRACTIONS [Archives:1998/43/Culture]
0. Back ground
The Yemen Republic covers an area of about 550,000 km2, has a population estimated at 16 million, the main land coastline of the Red Sea extends about 250 nautical miles in a roughly north-south direction. Yemen has a continental shelf of 3,500 square nautical miles with a depth less than 200 m.
The coastline lies on the eastern shores of the Red Sea from about latitude 12 40 N to latitude 15 25 N.
– Coral reefs form the basis for the commercial and artisanal fisheries of the Red Sea.
– Many animal species depend, directly or indirectly, on coral for their food requirement.
– Coral reefs are important to man, supplying high quality protein through their associated fish and shellfish components (Sohannes, 1970; 1975):
These food stuffs may be a critical factor in the development of tropical islands or coastal desert communities.
– Numerous reef inhabitants have also been found to be to source of various pharmaceutical compounds (Sohannes, 1970a; McEnroe and Fenical, 1978).
– GPS position is the main site identification, site number is merely a tag for the data sheet and database record.
– Under water data sheets we record water temperature, salinity, and visibility.
– A visual estimate of the percent bottom cover of the main sessile benthos categories (hard coral, soft coral, etc.).
– Scuba diving, linetransect 50m, random places for three transect.
– Underwater camera.
– Temperature loggers fixed for six months.
Corals are animals and go through a larval stage.
The larvae settle on hard substrate and proceed to grow, but high levels of sedimentation or turbidity can mechanically black the feeding polyps and prevent growth.
Some corals are quite adept at removing sediments but the symbiotic algae called zooxanthellae contained in the coral tissues require light to produce food. While some corals can capture enough plankton from the water in order to live and grow, others have enough zooxanthellae to produce sufficient food for growth in the absence of plankton. Very few coral can survive if their plankton feeding apparatus is blocked and insufficient light is available for photosynthesis by the zooxanthellae. Nevertheless, some corals are able to survive these conditions, but have a limited food supply and, therefore, grow slowly. Thus, recovery of corals is expected to be slow.
The morphology of some Scleractinia corals may be affected by independent environmental factors such as the availability of food and the ambient light intensity.
A species having a wide depth distribution may exhibi several growth forms and/or colonies may become less robust, more slender, or flattened with increasing depth.
The optimum temperature for growth is 26C (Coles and Jokiel 1978). The minimum sea surface temperature is 18C (Vaughan and Wells 1943).
– Some types of sponge are important in accreting coral skeletons in deeper waters where light is limited and coral growth rudimentary. Also some sponges are significant contributors to the net primary productivity of reef systems.
– “Boring” and “burrowing” sponges, found on most coral reefs, chemically dissolve (etch) calcitic and aragonitic substrates including live corals; cause the phenomenon of “coral bleach-ing”, and sometimes result in the destruction of large tracts of coral reef.
Some of the etching chemicals are also toxic to humans, denaturing proteins.
4. Survey Results
– Large areas of coral reefs exit in Yemen’s Red Sea water. All islands and shoals surveyed to the north and west of Hodeidah have adjacent reef complexes. Some of the coral on these reefs are dead, but this is believed to be a recent phenomenon.
– The limited areas surveyed to the south of Hodeidah showed reef development.
– Most of the areas of reef surveyed south of Ghulayfiqah had less coral mortality.
– Reefs in Bab Al-Mandeb and north of Dhubab were in good condition with a high percentage of live coral.
– Most reefs surveyed contained a large fish population.
– The distribution of habitat types along the Red Sea coast of Yemen roughly divides the coast into three sections:
¥ The northern part from the Saudi border to Ras Isa is a relatively lower energy environment, protected from heavier seas by offshore islands and reefs, mainly dominated by mangroves with seagrass beds in bays and patches along the coast and reef patches off the coast and around the islands.
¥ The central section near to Khawkhah, has some seagrass, but is mainly long sandy shores in a higher energy environment.
¥ The southern section which extends to Bab Al-Mandeb, has fringing reef along most of the coastline with moderate energy and clearer water.
– Temperatures took from loggers in Bab Al-Mandeb (27 C- 34.5 C) south of the Red Sea, and Luhaya in the north is (27 C- 32 C).
4.1 Types of Reef
– Shallow and short to expended reef flat usually has a sandy bottom and small patches of hard substrate, and terminates with a hard edge that drops to a similar unstable bottom.
– The width of the reef flat could extend from several tens of meters to over 2km. Many have patches of flashy macro algae or seagrass meadows in the shallows.
– The hard coral species to be found in the shallowest part of reef flat is Stylophora Pistillata Savignana.
– The hard edge of the flat was mainly composed of massive colonies and sometimes plating Acropora and occasionally small beds of branching Acropora. On the sandy flat at the bottom of the slope were often a sparse scattering of massive corals of the genus porites and family favidea.
4.2 Collection of Biological Specimens
Over 200 samples of hard coral specimens were collected. These were bleached, labeled and identified. Of these 72 were Acropora.
4.3 Dead Coral
Coral may die from a wide variety of natural causes (Antonious 1977). However, the most serious diseases are white band disease and black band disease (Antonious. 1973; 1976; 1977; 1982a, b). Several coral colonies exhibited the “bleaching” phenomenon whereby coral has been “stressed”. Such stresses include abrasion, increased turbidity, pollution, disease and sudden changes in temperature and/or salinity.
Also releasing zooxanthellae was the result of the scraping type of feeding behavior of the Red Sea urchin diadoma setosum.
Another possible coral predator observed was the crown of thorn starfish, Acanthastr planci.
4.4 Physical (Mechanical) Damage
Corals are undoubtedly very well adapted to the kind of physical destruction (fragmentation, etc) that heavy wave action produces, and apparently it makes no difference whether these waves are generated by a hurricane or shock-waves generated by an explosion (Antonious and Weiner, 1982).
While hurricanes have occasionally annihilated reefs (Stoddart, 1963), and have caused considerable breakage (Antonious, 1972), resulting in large amounts of rubble (Shinn, 1972), coral rubble does not typically originate from damage to live, healthy colonies. Rather, it is produced from colonies which have been dead for some time, with their skeletons weakened by boring algae, sponges, and other invertebrates (Antonious and Weiner, 1982).
– Increased turbidity associated with physical/mechanical impacts (Chalker, 1976), (Back; 1978) suggests that the primary effect of turbidity on the calcification rate is through reduced light availability.
– (Back and Engel 1979) observed that one-third of all juvenile colonies died or disappeared during six months of observation; the results were the same for all species and all species groups. Since skeletons of the juveniles were not found, the cause of this mortality was attributed to perdition by grazing.
The coral reefs in Yemen (Red Sea) are not extensive for a number of reasons. The most significant limiting factor is likely to be the rarity of hard substrates suitable for coral settlement.
This is because of the great depth of alluvial sediments on the Tihama and shallow coastal shelf. Secondly, the shallow bathymetry of the region combined with strong reasonal south south-westerly winds leads to rough weather, destablization of soft substrates, high turbidity and sediment stress. Finally there may be localized salinity and sediment stresses resulting from flash foods.