Present Environmental Status of the Shuaiba Lagoon, Red Sea Coast, Saudi Arabia

JKAU: Mar. Sci., Vol. 22, No. 2, pp: 159-179 (2011 A.D. / 1432 A.H.) DOI : 10.4197/Mar. 22-2.9 Present Environmental Status of the Shuaiba Lagoon, Red Sea Coast, Saudi Arabia Ramadan H. Abu-Zied, Rashad A. Bantan and Mohamed H. El Mamoney Marine Geology Department, Faculty of Marine Science, King Abdulaziz University, P.O.Box 80207, Jeddah 21589, Saudi Arabia email: rabuzied@kau.edu.sa Abstract. Shuaiba Lagoon is located about 80 km south of Jeddah city, Saudi Arabia. Its environmental characteristics were determined. The macro-fauna and flora were also sampled and identified. Extreme values for salinity (60 ) and water temperature (33 C) were recorded and that may be due to its shallowness and small volume and occurrence under arid warm climate. Lagoon water ph was low (8.3), likely, as a result of re-mineralization of organic matters. These extreme variables exerted probably a stressful natural environment on the calcareous macro-fauna (molluscs and corals) as indicated by dominance of gastropod Cerithidea pliculosa and pelecypod Mytilus edulis in the lagoon. Corals could not tolerate these conditions so they were only recorded close to the inner- and outside inlet of the lagoon. On the contrary, these environmental conditions are probably favorable for mangroves, seagrasses and macro-algae (and Cyanophytes) as indicated by their proliferation in the lagoon. Keywords: Seagrasses, Cyanophytes, Hypersaline, Corals, Intertidal Area, Inlet. Introduction Shuaiba lagoon is located about 80 km south of Jeddah city (Saudi Arabia) on the eastern Red Sea coast, with a total area of approximately 14.3 km 2 (this study). It is situated between latitudes 20 42 to 20 51 N and longitudes 39 26 to 39 32 E (Fig. 1). It has an elongated shape with long axis (8 km length) parallel to the Red Sea coast and a 159

160 Ramadan H. Abu-Zied et al. maximum width of 3 km (Fig. 1). The Shuaiba Lagoon is connected with the Red Sea via a narrow, deep inlet (mouth) that is located at its southern side (Fig. 1). At its northern side, there is a narrow, shallow tidal creek connecting it with a smaller lagoon. But this tidal creek has been closed by artificial alluvium due to road construction. A considerable part of the Shuaiba Lagoon area (10%) is covered by mangroves (total area of 1.42 km 2 ) with a height of ~3 m (Fig. 1). The Shuaiba Lagoon is a back-reef lagoon. Its western side is bordered by old, raised coral reef terraces, probably of Pleistocene age (Skipwith, 1973; Al-Sayari and Zotl, 1978; Bahafzallah and El-Askary, 1981; El-Sabrouti, 1983; Behairy, et al., 1987; and Al-Washmi, 1999) with elevations ranging from 1 to 3 m a.s.l. These raised terraces make a natural condition protecting the lagoon from strong waves, therefore many mangroves are able to survive and develop (Hariri, 2008). The other sides of the lagoon are bordered by low land (0.5-1 m a.s.l) which are composed of sand-sized alluvium and sabkha. Tidal range at the Shuaiba Lagoon is very small similar to that of the central Red Sea (25 cm), see Lisitzin (1974). It is semi-diurnal generated by tidal force in the Red Sea and co-oscillating tide of Gulf of Aden (Al-Barakati, 2010). The Shuaiba Lagoon is one of the Red Sea coastal lagoons that break the continuity of the Pleistocene reef complexes and remain as remnant of much larger body of water (Al-Washmi, 1999). It was formed by erosion in the pluvial Pleistocene and drowned by post glacial sea level rise during the Holocene (Braithwaite, 1987; and Brown et al., 1989). Occurrence of raised coral reef terraces (Pleistocene age) in the western side of the Shuaiba Lagoon might indicate that it is a remnant of a Pleistocene back-reef system filled by Red Sea water during the Holocene transgression. However, Rabaa (1980) suggested that some lagoons of the Red Sea were probably formed as a result of collapse structures resulting from the selective solution of Miocene evaporite beds underlying the younger succession. Many studies (e.g., Ahmed and Sultan, 1992; Al-Washmi and Gheith, 2003; Hariri, 2008; and Al-Barakati, 2010) have dealt with the Shuaiba Lagoon in regard to its meteorology and water circulation, diagenesis of sediments and microfossils, but no attention has been paid to its environmental characteristics. Ahmed and Sultan (1992) reported that the exchange of water between Shuaiba Lagoon and the Red Sea was

Present Environmental Status of the Shuaiba Lagoon, Red Sea Coast, Saudi Arabia 161 mainly forced by the local winds, whereas seasonal mean sea level variations did not have a significant effect on the flushing of this lagoon. However, Al-Barakati (2010) concluded that water circulation in the Shuaiba Lagoon is mainly dominated by tidal force. Al-Washmi and Gheith (2003) concluded that the coastal sabkha sediments of Shuaiba lagoon have undergone diagenetic processes due to dominance of dolomitic minerals. Hariri (2008) studied the benthic foraminifera of bottom sediments of the Shuaiba Lagoon and suggested that they were mainly controlled by factors such as: water depth, light, sediment grain size and freshwater inputs. Fig. 1. A map showing the Shuaiba Lagoon and stations sites (plus sign). Mangroves are indicated by black areas.

162 Ramadan H. Abu-Zied et al. The main objective of this study is to measure the prevailing environmental parameters (e.g., water depth, temperature, salinity and ph), assess their impact on the macro-fauna and flora of the Shuaiba Lagoon and their inter-relationship, if possible, with the prevailing arid, warm conditions. Materials and Methods Fifty two stations were selected for sediment samples and measured for the environmental parameters such as water depth, temperature, salinity and ph. At each station, macro-fauna and flora were also separated and described. Temperature, salinity, ph and dissolved oxygen for the lagoon surface water were measured, in situ, during May 2010 using Hach HQ40D a multi-parameters meter. High salinity water samples were diluted with known-volume distilled water before measurement. Only Temperature and salinity were measured for the water column at some stations. Water depth was measured using a graduated bar. All of these measurements and their coordinates (assigned by Garmin II GPS) were listed in Table 1. Table 1. Stations coordinates, measured environmental parameters (May 2010) and main type of macro-fauna and flora in Shuaiba Lagoon. Sample No Latitude Longitude Depth Salinity Temperature ph (N) (E) (m) (surface, ) (surface, C) Macro-fauna and flora SH1 20.73333 39.49137 0.25 8.35 46.4 29.8 SH4 20.73327 39.49178 1.2 8.43 43.2 29.7 SH5 20.73333 39.49123 0.15 8.34 47.8 30.1 SH6 20.73757 39.48647 0.35 8.35 49 30.1 Algae SH7 20.7379 39.48683 0.5 8.38 48 29.6 SH8 20.7379 39.48683 0.5 8.38 48 29.6 Seagrasses SH9 20.73817 39.48747 1 8.41 45.8 29.3 Seagrasses SH10 20.7447 39.4785 0.2 8.36 46.2 33.7 Algae SH11 20.7455 39.47947 0.7 8.41 45.4 32.9 Seagrasses SH11B 20.7455 39.47947 0.7 8.41 45.4 32.9 Seagrasses SH12 20.74593 39.480846 1.5 8.42 45.2 30.2 Seagrasses and algae SH13 20.75577 39.46832 0.1 8.39 61.6 30.7 Algae SH14 20.75635 39.46985 0.4 8.35 46.6 30.7 Seagrasses and algae SH15 20.75675 39.47113 0.9 8.45 41.6 30.3 Seagrasses and algae SH16 20.76483 39.45897 0.15 8.42 61 30.2 Small molluscs SH17 20.7645 39.46113 0.25 8.39 49.4 30.7 Small molluscs SH18 20.7666 39.46295 0.25 8.35 47.8 30.8 Small molluscs SH19 20.77192 39.46042 0.35 8.21 53.7 33.6 Small molluscs SH20 20.7786 39.45832 1 8.22 53.3 33.7 Small molluscs SH21 20.78309 39.45232 0.6 8.3 55.8 31.9 Small molluscs SH22 20.78475 39.45849 0.6 8.32 56.2 30.9 Small molluscs SH23 20.77209 39.46886 0.5 8.27 51.3 30.5 Small molluscs SH24 20.77277 39.47965 0.3 8.3 52.8 31.3 Algae

Present Environmental Status of the Shuaiba Lagoon, Red Sea Coast, Saudi Arabia 163 Sample No Latitude Longitude Depth Salinity Temperature ph (N) (E) (m) (surface, ) (surface, C) Macro-fauna and flora SH25 20.77371 39.47966 0.15 8.42 54.1 33.3 Algae SH26 20.76134 39.49425 0.7 8.37 58 31.2 Small molluscs SH27 20.76178 39.49698 0.4 8.36 57.8 32.2 Small molluscs SH28 20.75303 39.49561 1.1 8.47 46.3 30.1 Seagrasses and algae SH29 20.74456 39.50339 0.2 8.46 46 33.2 SH30 20.74473 39.50211 0.7 8.51 45.8 31.9 Seagrasses and algae SH30A 20.74473 39.50211 0.7 8.51 45.8 Seagrasses and algae SH31 20.73866 39.49544 0.8 8.52 43 31 Coral and algae SH31A 20.73866 39.49544 0.8 8.52 43 31 Coral and algae SH32 20.72791 39.48546 0.3 8.5 40.9 30.8 Coral and algae SH33 20.727 39.48367 0.7 8.57 38.8 30.5 Coral and algae SH34 20.73597 39.47488 1.35 8.58 38.9 31.1 Coral and algae SH35 20.73807 39.47749 0.6 8.6 39 33.2 Coral and algae SH36 20.73856 39.47801 0 8.6 39 33 SH37 20.7648 39.48666 0.3 8.2 48.9 32.5 Algae SH38 20.75925 39.49547 0.1 8.25 56.3 33.4 SH39 20.7328 39.49982 0.45 8.51 41.5 32.5 SH39B 20.72852 39.48865 6.75 8.45 38.3 28.7 SH40 20.73097 39.47945 15 8.48 38.3 29.3 SH41 20.72572 39.48278 7 8.62 38.3 30.5 SH42 20.73355 39.49379 2 8.5 38.4 29.2 SH43 20.73856 39.49135 2 8.43 39.1 29.9 SH44 20.74444 39.49119 2.5 8.53 40.9 29.2 Algae SH45 20.74679 39.4966 2.7 8.51 40.3 29.1 Algae SH46 20.74696 39.49325 1.8 8.54 42.7 29.3 Algae SH47 20.75085 39.48991 1.7 8.52 43.2 29.5 Algae SH48 20.75206 39.48216 2.2 8.48 46.4 30.3 Algae SH49 20.75551 39.47851 2.1 8.48 46.9 29.7 Seagrasses and algae SH50 20.76078 39.48161 1.3 8.19 47.5 30.3 Seagrasses and algae SH51 20.75856 39.47544 1.2 8.47 47.5 30.8 Seagrasses and algae Results 1- Bathymetry Shuaiba Lagoon is a shallow basin with the depth ranging from 1 m (max.) in the north and 3 m (max.) in the south. Its northern part is very shallow (~0.4 m) showing a maximum depth of 1 m at its centre (Fig. 1). The southern part of the lagoon is the deepest part in the lagoon (~3 m). The northern and southern parts of the lagoon are separated by a wide, shallow tidal flat with a sand-sized shoal that is entirely populated by mangrove trees (~3.5 m height) (Fig. 2). Immediately before the inner inlet (mouth) of the lagoon, depth varies from 1 to 1.5 due to occurrence of raised substrates. After that, depth increases rapidly reaching 7 m throughout the inlet and continues to reach more than 15 m in the outer part of the inlet (Fig. 2).

164 Ramadan H. Abu-Zied et al. Fig. 2. Bathymetry map of the Shuaiba Lagoon. Isobath interval is 0.5 m. 2- Temperature Surface water temperature of the lagoon s inlet and the southern part of the lagoon is the lowest ranging from 29 to 30 C (Fig. 3). This (low temperature) surface water is remarkably traceable at the central part of the lagoon, indicating the movement of Red Sea water as surface inflow into the most parts of the lagoon (Fig. 3). In the northern part of the lagoon, the surface water temperature increases to a high value of ~33 C (Fig. 3). It is also high (>31 C) at areas close to the lagoon s beaches, especially at the eastern and western sides (Fig. 3).

Present Environmental Status of the Shuaiba Lagoon, Red Sea Coast, Saudi Arabia 165 Fig. 3. Distribution pattern of surface water temperature in the Shuaiba Lagoon during May 2010. Contour interval is 0.4 C. 3- Salinity Surface water salinity of the Shuaiba Lagoon follows the pattern of surface water temperature. In general, it is very high with a mean value of 47 ±6. At the inlet (mouth), it shows a value of 39 indicating the presence of Red Sea surface water (Fig. 4). Then, it increases gradually inwards the lagoon until it reaches its maximum (56 ) at the northern part of the lagoon. This indicates that inside the lagoon, the surface water moves towards the north. The surface water salinity becomes very high

166 Ramadan H. Abu-Zied et al. (> 50 ) in the areas that are close to the lagoon s beaches, especially at the eastern and western sides (Fig. 4). Fig. 4. Distribution pattern of surface water salinity in the Shuaiba Lagoon during May 2010. Contour interval is 1. 4- ph Surface water ph of the Shuaiba Lagoon shows, in general, a weak negative relationship with the surface water salinity and no relationship with temperature (Fig. 5). It is high at the inlet and the southern part of the lagoon with a mean value of 8.5 which is similar to that of the Red

Present Environmental Status of the Shuaiba Lagoon, Red Sea Coast, Saudi Arabia 167 Sea water (Fig. 6). At the northern and north-eastern parts of the lagoon, the ph decreases displaying a mean value of 8.2 (Fig. 6). It is remarkable to see that the ph is low in the areas that are dominated by mangroves. Fig. 5. Scatter diagram showing relationship among surface water ph, salinity ( ) and temperature ( C) in the Shuaiba Lagoon during May 2010.. Fig. 6. Distribution pattern of surface water ph in the Shuaiba Lagoon during May 2010. Contour interval is 0.04.

168 Ramadan H. Abu-Zied et al. 5- Water Circulation The water column of the Shuaiba Lagoon is only 2 m thick. Based on measurements of temperature and salinity, its structure shows two distinctive layers, especially in the southern part of the lagoon. The cooler (29.5 C), less saline (38 ) water of the Red Sea enters the lagoon as surface inflow which is forced by tides and local winds (Ahmed and Sultan, 1992; and Al-Barakati, 2010). This surface inflow remains traceable up to the middle of the lagoon. Then, it gets more dense and hypersaline to sink and creep on the floor of lagoon, occupying nearly the lower 1 m of the water column (about 2 m thick) in the lagoon (Fig. 7). It enters the Red Sea as subsurface outflow with warm and hypersaline conditions, occupying the lower 3 m of the water column (6-7 m thick) of the inlet/mouth (Fig. 7). Outside the lagoon, this hypersaline subsurface outflow is still present and creeps on the floor occupying the lower 7 m of the water column (15 m thick) at the Station SH40 (Fig. 7). This water circulation allows renewal of the lagoon water within 1-2 days (Al-Barakati, 2010). Fig. 7. Distribution of salinity and temperature against depth in the water column of Shuaiba Lagoon during May 2010 at stations SH48, SH44, SH39A and SH40. See Fig. 1 for the location of these stations. Bottom substrates are indicated by hatched areas.

Present Environmental Status of the Shuaiba Lagoon, Red Sea Coast, Saudi Arabia 169 6- Macro-Fauna and Flora Mangrove trees are mainly of Avicennia marina dominating other macrophytes (e.g., seagrasses, and macro-algae) in the Shuaiba Lagoon (Fig. 8A). Mangroves occupy 10% of the total area of lagoon and are located in tidal flat areas with water depths less than 0.2 m (Fig. 1). They were found growing in firm, hard and soft substrates, as well as in sandsized, raised shoals. The soft substrate consists of black mud probably due to decomposition of organic matter. The mangroves in the Shuaiba Lagoon reach a maximum height of 4 m tall, occupying the areas that are located at the intertidal-subtidal boundary to enable their pneumatophores (aerial roots) to breathe air in habitats that have waterlogged soil. Seagrasses (e.g., Enhalus acoroides and Cymodocea sp.) occupy slightly deeper environments than those of the mangroves. They are recorded at areas of 0.5 to 1.5 m depths and having a maximum height of 35 cm (Fig. 8B, D). Their substrates vary from firm to soft. Their green leaves are sometimes spotted by white color of larger foraminifer Sorites orbiculus. Many macro-algae such as: Caulerpa ethelae (sea grapes), Caulerpa racemosa, Laurencia obtusa, Halimeda tuna (coralline alga) and Turbinaria conoids (turbinweed) inhabit the Shuaiba Lagoon (Fig. 9). Cyanophytes (green filamentous algae) occur at the periphery of the lagoon where the substrate is muddy. They grow forming a thick algal mat patches at northern region of the lagoon, especially at the intertidalsupratidal zone (sabkha) (Fig. 12D). The species Caulerpa ethelae (sea grapes) (Fig. 9B) dominates the bottom at the middle area of the lagoon and it is sporadically recorded in the intertidal area of the northern area. Just before the inlet (inner inlet), the brown algae Laurencia obtuse, Turbinaria conoids (turbinweed) (Fig. 9D, F) and the funnel weed Padina boryana (Fig. 10A) grow more abundantly attached to hard substrates. They proliferate also just outside the lagoon. The calcareous green algae (Halimeda tuna) inhabit the tidal area outside the lagoon (Fig. 9E). Stony corals (Porites sp. and Stylophora pistillata; Fig. 11B, C) and sponge Pericharax heteroraphis (calcareous sponge) (Fig. 11A) were commonly found on hard substrates, immediately outside the lagoon and

170 Ramadan H. Abu-Zied et al. close to the inner inlet. In the other parts of the lagoon, these organisms disappear. Fig. 8. Macrophytes from the Shuaiba Lagoon. A: the common mangrove Avicennia marina; B: Seagrass Enhalus acoroides; C & D: Seagrasses, Cymodocea sp. Small gastropod (Cerithidea pliculosa) and pelecypod (Mytilus edulis) shells are the most abundant molluscs in the lagoon. They dominate the substrates of the tidal flats of the northern part of the lagoon. When they die, they accumulate on the shoreline, comprising a significant part of the shore shingle (see Fig. 12B, C). At stations (SH26

Present Environmental Status of the Shuaiba Lagoon, Red Sea Coast, Saudi Arabia 171 and SH27), the small pelecypod Mytilus edulis is the more prolific species, living in colonies, so their byssi intricate forming a thick mussel mat. Large gastropod Strombus tricornis and pelecypod Tridacna sp. shells are recorded on raised shoals at the eastern side of the lagoon. Strombus tricornis shells are more frequent at the shoreline of the southeastern side of the lagoon, especially near the inlet (Fig. 11D). Fig. 9. Macro-algae from the Shuaiba Lagoon. A: green alga; B: sea grapes Caulerpa ethelae; C: Caulerpa racemosa; D: Laurencia obtusa; E: coralline alga, Halimeda tuna; F: turbinweed, Turbinaria conoids.

172 Ramadan H. Abu-Zied et al. Fig. 10. Macro-algae, hydrozoan & sponge from Shuaiba Lagoon. A: funnel weed, Padina boryana; B: hydrozoan, Sertularella; C: sponge weed, Ceratodictyon spongiosum; D & E: Sponge, Strepsichordaia lendenfeldi.

Present Environmental Status of the Shuaiba Lagoon, Red Sea Coast, Saudi Arabia 173 Fig. 11. Macro-benthos from Shuaiba Lagoon. A: calcareous sponge, Pericharax heteroraphis; B: stony coral, Porites sp.; C: stony coral, Stylophora pistillata; D: gastropod, Strombus tricornis.

174 Ramadan H. Abu-Zied et al. Fig. 12. Macro-benthos & green algae from the Shuaiba Lagoon. A: a bivalve, Tridacna sp.; B: small shells of Mytilus edulis and Cerithidea sp.; C: small shells of Cerithidea sp.; D: dry cyanophytae (green algae).

Present Environmental Status of the Shuaiba Lagoon, Red Sea Coast, Saudi Arabia 175 Discussion Shuaiba Lagoon occurs in warm, arid region and it is a shallow (~1 m depth) small basin that connected with the Red Sea water by a very narrow passage (c. 60 m wide and 6 m deep). Thus, it is a sensitive basin for both climatic and environmental changes. Its water physico-chemical and biological characteristics are unique and almost different from those of the Red Sea. The surface water temperature of the Shuaiba Lagoon reaches 33 C during May 2010, especially in the northern part, exceeding that of the Red Sea water by about 3 C. These conditions make the Shuaiba Lagoon as a concentration basin, and consequently, its surface water salinity increases to very high levels up to 60. This high salinity water sinks to enter the Red Sea via the inlet as subsurface outflow indicating an active lagoonal circulation in this small basin. This circulation is likely to be mainly affected by density saline currents (i.e. haline circulation). Ahmed and Sultan (1992) concluded that the exchange of water between Shuaiba Lagoon and the Red Sea is forced by the local winds that play a variable but sometimes dominant role in the flushing of the lagoon, whereas tidal exchange is greatly affected by force and direction of wind, caused by the large diurnal differences in local heating. They also reported that seasonal mean sea level variations do not have a significant effect on the flushing of the Shuaiba Lagoon. In spite of occurrence of high temperature and salinity in the northern part of the Shuaiba Lagoon that could hinder diffusion of atmospheric CO 2 into lagoon water leading to ph increase, the lowest ph was recorded in this area. The explanation for this is that the occurrence of high temperature in this area could enhance re-mineralization of organic matters (mangrove litters and algal thalli) and consequently releasing more CO 2 into the waters and this leads to decrease of water ph. This low ph could be a detrimental on the calcareous fauna (e.g., foraminifers and molluscs) and flora. Prevalence of extreme temperature and salinity and low-energy, sheltered environments in the Shuaiba Lagoon allowed, however, occurrence of unique fauna and flora in this lagoon such as molluscs, macro-algae, soft hydrozoans, mangroves and seagrasses. Mangroves occur preferentially in the intertidal area of the lagoon, dominating the intertidal zone with tall and healthy trees. In the intertidal-supratidal zone, they are short, showing many dead branches indicating existence of

176 Ramadan H. Abu-Zied et al. stressful environmental conditions in this area. The recorded molluscs belong only to pelecypod species Mytilus edulis (forming shell mat in some places) and gastropod species Cerithidea pliculosa. The Cerithidea species is adapted to live in a wide ecological gradient from freshwater to hypersaline and lacustrine environments and have a salinity tolerance of 3-100 (Plaziat 1993). Such species occur commonly in intracontinental salt lakes (Plaziat and Younis 2005; and Abu-Zied et al., 2011). These two species dominate the molluscs in the upper Shuaiba Lagoon, indicating also existence of stressful environmental conditions. Slobodkin and Sanders (1969) and Pielou (1975) mentioned that under severe environments one or two species colonize the niches very rapidly giving high numbers of individuals, resulting in low diversity and causing extinction of marginal species. Hard (aragonitic) corals are completely absent from the water of the lagoon. They occur only around the lagoon inlet where normal Red Sea waters predominate and optimal conditions for corals occur within temperature of 25-30 C and salinity of 37 (Wright and Burchette, 1996). They also reported that in tropical and subtropical shallow water; the temperature consistently over 20 C and salinities 32-40 ; so carbonate producers are as calcareous green algae (Halimeda) and hermatypic, symbiont-bearing corals that cannot tolerate high salinities, but green algae are able to continue producing sediments. The seagrasses (e.g., Enhalus acoroides and Cymodocea sp.), macro-algae (e.g., Caulerpa sp., Laurencia obtuse and Turbinaria conoids) and coralline algae dominate the bottom sediments of the Shuaiba Lagoon where extreme temperature and salinity occur. Also, cyanophytes (green filamentous algae) occur on the periphery of the lagoon, forming a thick algal mat at some patches in the northern area of the lagoon, especially at the intertidal-supratidal zone. This indicates that these flora are able to withstand extreme high salinity and temperature. However, persistence of such extreme environmental conditions and dominance of these floral associations might be a resultant of prevalence of warm, arid climatic conditions upon a small volume of water within the Shuaiba Lagoon (Meshal, 1987). Dominance of macro-algae at the expense of aragonitic corals in the modern sea was attributed to the greenhouse gas-induced global warming (Hallock, 1999). We suggest that the present environmental conditions and faunal/floral associations of the Shuaiba Lagoon might represent a modern analogue for the

Present Environmental Status of the Shuaiba Lagoon, Red Sea Coast, Saudi Arabia 177 warming interval that occurred in geologic past. During Eocene, disappearance of aragonitic corals from shallow-water carbonate environments and dominance of coralline algae and bryozoans were used as an indication of warming conditions accompanied with high levels of atmospheric CO 2 (Berner, 1994; and Hallock, 1999, 2001). Conclusions The Shuaiba Lagoon is a back-reef, shallow basin (~1 m deep) connected with the Red Sea via a very narrow passage (about 60 m wide and 6 m deep). It is characterized by occurrence of extreme natural environmental conditions due to prevalence of warm, hypersaline waters with low ph when compared with the normal Red Sea water. This warm, high saline water goes out from the lagoon to the Red Sea as a subsurface outflow via the deep inlet (7 m water depth). These extreme natural conditions allowed low diverse but high abundance of calcareous macrofauna to occur in this lagoon. On the other hand, these conditions are probably favorable for mangroves, seagrasses and macro-algae as indicated by their dominance in the lagoon. Cyanophytes occur predominately at the intertidal-supratidal zone, indicating their tolerance to extreme high salinity and temperature. Aragonitic corals were only observed around the inlet where normal Red Sea waters predominate. Acknowledgement This research was funded by the Deanship of Scientific Research, King Abdulaziz University, Project No. 430/005-8. Early version of this paper was read by Nuzhat Hashimi. Adel Guirguis is thanked for the identification of macro-algae. We are also grateful to the anonymous reviewers for their useful comments. References Abu-Zied, R.H., Keatings, K., Flower, R.J. and Leng, M.J. (2011) Benthic foraminifera and their stable isotope composition in sediment cores from Lake Qarun, Egypt: changes in water salinity during the past ~500 years, Journal of Paleolimnology, 45: 167-182. Ahmed, F. and Sultan, S.A.R. (1992) The effect of meteorological forcing on the flushing of Shuaiba Lagoon on the eastern coast of the Red Sea, JKAU: Mar. Sci., 3: 3-9. Al-Barakati, A.M.A. (2010) Application of 2-D tidal model, Shoaiba Lagoon, eastern Red Sea coast, Canadian Journal on Computing in Mathematics, Natural Sciences and Medicine, 1: 9-20. Al-Sayari, S.S. and Zotl, J.G. (1978) Quaternary Period in Saudi Arabia, V.I, Springer-Verlag, Wein, New York, 335 p.

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Present Environmental Status of the Shuaiba Lagoon, Red Sea Coast, Saudi Arabia 179 - - -.. ( ph ).. ( ) ( ).. ( )..