OCEANOLOGICA ACTA 1985- VOL. 8- W 4 ~ -----·~- Red Sea Tiran Island Benthic fishes Community structures The communities of benthic fish Species richness Mer Rouge Ile de Tiran in Foui Bay (Tiran Island, Red Sea) Poissons benthiques Structure de la communauté Richesse en espèces Menachen GOREN, Ehud SPANIER Department of Zoology, George S. Wise Faculty of Life Sciences,Tel Aviv University, Ramat-Aviv 69978 Tel-A viv, Israel. Department of Maritime Civilizations and Center for Maritime Studies, University of Haïfa, Mount Carmel, Haifa 31999, Israel. Received 11/3/85, in revised form 6/6/85, accepted 7/6/85. ABSTRACT The study was conducted on benthic communities of fishes in Foui Bay (Tiran Island, Northern Red Sea). 1588 fish assigned to 154 species were collected at six stations. The number of species at each station ranged from 21 to 64. The values of species s diversity (H=- L (Pi log Pi)) were found to be relatively high: 2.0050-5.5500, as i=l were the values of the evenness rate (J =H/Hmax): 0.3742-0.952 8. The values of s similarity between each couple of stations (A/=[2- L IPiJ-PiKI.50]) were found 1=1 to be low: 7.25%-41.38%, as were the proportions of species common to each couple of stations: 10.87-29.59%. The richness of species of the leading families is compared with that of the entire Red Sea and that of the reef community of northern Entedebeer Island. The ecological significance of these findings and the uniqueness of Foui Bay in its tropical surroundings are discussed. Oceanol. Acta, 1985, 8, 4, 471-478. RÉSUMÉ Les communautés de poissons benthiques dans la baie Foui (île de Tiran, Mer Rouge) Cette étude porte sur les communautés benthiques des poissons de la baie Foui (île de Tiran, nord de la Mer Rouge). 1 588 poissons appartenant à 154 espèces ont été récoltés dans 6 stations. Le nombre d'espèces dans chaque station varie entre 21 et s 64. On constate que les valeurs de l'indice de diversité spécifique (H = - L Pi log Pi) i=l sont relativement fortes (2,005-5,550), de même que celles de l'équitabilité (J =H/ Hmax) égales à 0,374-0,953. La similarité entre les stations prises deux à deux (7,25- 41,38 %) ainsi que le pourcentage du nombre d'espèces qui leur sont communes (10.8- 29.59 %) sont faibles. La richesse spécifique des principales familles de la baie Foui est comparée à celle de la Mer Rouge considérée dans son ensemble ainsi qu'à celle de la communauté récifale située au nord de l'île Entedebeer. La signification écologique de ces résultats et la particularité de la baie Foui par rapport à son environnement tropical sont discutées. Oceanol. Acta, 1985, 8, 4, 471-478. INTRODUCTION features of this small desert island is its inner bay. This bay, known as Foui Bay, reaches deep into the island. The Island of Tiran (Fig. 1) is a part of the complex Since it is protected from the intense currents prevail­ of Midian Islands, situated in the straits of Tiran, ling on both sides of the island (Klinker et al., 1976), separating two zoogeographical subdivisions-the Red the water of the bay is relatively calm. These conditions Sea proper in the south and the Gulf of Elat (Gulf of have brought about an ecological environment of a Aqaba) in the north. One of the unique geographical large shallow bay, the bottom of which is covered with 0399-1784/85/04 471 08/$ 2.80/(0 Gauthier-Villars 471 M. GOREN, E. SPANIER Figure 1 Map of Tiran Island showing the locations of the sampling stations. 1, the camp of the first expedition; 11, the camp of the second expedition. MARSA BHU,BEER EL·QURIN TIRAN ISLAND soft sediment, in contrast to the rest of the island which elima te of the island and its surroundings are of defini te is surrounded by an exensive area of coral reefs and desert character, with extremely high summer tempera­ exposed to intense current and wave action. There are tures and very little, or no precipitation. A constant, a few similar formations in the Gulfs of Elat and Suez, and at times fairly strong northerly wind predominates but ali are much smaller than Foui Bay. The fact that through the Gulf of Eilat toward Tiran. There are this island is remote, with no freshwater sources, bas intense currents around the island. Waters are clear prevented human settlement; th us, the underwater habi­ with a low primary production (Levanon-Spanier et tats remain completely undisturbed by man-made acti­ al., 1979). These conditions are ideal for the deve­ vity. These circumstances provide a rare opportunity lopment of fringing coral reefs. Off the southern coast for the faunistic and zoogeographical study of a unique of the island, where the offshore submarine slope is ecological formation typical to the Midian Islands, steep, the fringing reef rarely exceeds 50 rn in width which have not been studied up to the present. and sometimes is even entirely absent. The coasts with In addition to the faunistic information, the Tiran less submarine offshore slopes have correspondingly project permits a quantitative analysis of the fish com­ broader fringing reefs. The most extensive reefs are off munity of Foui Bay. Although the fish fauna of the the northern peninsula of the island which Schick Red Sea bas been investigated for about 200 years, and (1958) suggested should be classified as shoal reefs. more than a thousand papers and books report this There are also several developed coral formations in activity (Dor, 1984), only a few studies of community the opening of Foui Bay. Inside this bay, however, structure have been made. Fishelson et al., (1973), there are only very narrow reefs on the north coast, Bouchon-Navaaro (1980) and Bouchon-Navaro and and only small and flat coral outcrops along the Harmelin-Vivien ( 1981) described the species composi­ southern and eastern margins. Physical processes, such tion of certain families living in coral reefs. The single as currents and waves inside the bay, are of much comprehensive quantitative analysis of a fish commu­ smaller dimensions relative to the marine environment nity in the Red Sea was published by Clark et al. outside this gulf basin. Thus, the bottom of the bay is (1968). The present study throws more light upon this covered with a layer of soft sediment. 1t is unique also ecological aspect. with areas of dense growth of soft and delicate sea grass of the species Halophila stipulacea, H. ovalis, and H alodule uninervis (Lipkin, 1977). The latter is the pre­ ferred food of the Red Sea dugong Dugong dugong AREA OF STUDY (Lipkin, 1975) a marine mammal observed several times in Foui Bay including the present expedition. The Island of Tiran (Fig. 1) measures sorne 11 km north-south and 12 km east-west, with an area of 59 km2 (Schick, 1958). The highest point of the island is 502 rn above sea level (Goldberg, 1958), with a steep METHODS AND MATERIALS summit of ridges running along the southern coast of the island. North of this ridge, on either side of Foui The fish communities around Tiran Island were studied Bay, extends a plain which occasionally bas features of at 9 stations by the members of two expeditions conduc­ modest relief. The neck connecting the two parts of ted by the authors (Fig. 1). The first expedition the island is a low billy ridge (Goldberg, 1963). The (9 persons) took place from 1-6 June 1981, and the 472 FISH COMMUNITIES OF FOUL BAY (RED SEA) second (10 persons) from 21-26 September 1981. The Station 5 (4 June, 1981) present paper covers the data of the 6 stations inside Foui Bay (stations 4-9, Fig. 1). Shallow (0-1.5 rn) water with mostly rocky, and par­ tially sandy bottom, covered with small coral heads of The method of collecting fish in the various stations the genus Stylophora and sea grass of the genera was based on poisoning with pronoxfish (rotenon). The Halophila and Halodule. poison mixture - pronofish +sand - was prepared a short time before use to prevent spoilage by oxidation. Station 6 (22 September, 1981) The mixture was released close to the bottom by Shallow water with maximum depth of 1.5 rn with SCUBA divers. The fish were collected by skin and sandy bottom and low knolls, consisting of various SCUBA divers and preserved in formalin (4%). Large specimens (with TL>8 cm) were also injected with types of corals. formalin. The sampled fishes were identified and their total length was measured. The number of specimens Station 7 (29 September, 1981) per species were counted for each station. This was Depth 9-12 m. Sandy trenched bottom with coral done when the material was deposited in the Zoological knolls, coral plants and branched corals. Museum of Tel A vi v University. Bottom sediments were sampled at sorne of the stations. Station 8 (23 September, 1981) Grain size analysis of these samples was carried out Depth 8-10 m. The steep edge of a narrow fringing reef with the use of sieves. The insoluble residue of these with a sandy bottom at the foot of the escarpment. samples was also determined. Sediment analysis was performed at the Center for Maritime Studies, Uni­ Station 9 (24 September, 1981) versity of Haifa. Depth 0.5-1.5 m. Flat sandy bottom with a few flat The species diversity (H) for each station was calculated rocks broken by crevices and holes, covered partially using the formula offered by Shanon and Weaver s with various types of corals.