Environmental Biology of Fishes 54: 275–282, 1999. © 1999 Kluwer Academic Publishers. Printed in the Netherlands.
Fish colonization of an artificial reef in the Gulf of Elat, northern Red Sea Daniel Golania & Ariel Diamantb Department of Evolution, Systematics and Ecology, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel (e-mail:
[email protected]) b National Center of Mariculture, Israel Oceanographic and Limnological Research Ltd., Eilat, Israel (e-mail:
[email protected]) a
Received 15 September 1997
Accepted 10 August 1998
Key words: fish community, recruitment patterns, diversity Synopsis A small near shore artificial reef was constructed in the Gulf of Elat, northern Red Sea at a depth of 22–24 m. The colonization of fishes was monitored for a period of 728 days and a total of 94 species was recorded. Colonization was initially rapid. The first species to appear were Dascyllus trimaculatus and Chaetodon paucifasciatus (day 2). In the first seven months, a gradual increase in the number of species was observed, after which it leveled off. Subsequently, a reduction in the number of individuals increased diversity of the community, as measured by the Shannon & Weaver index. The low complexity of the major components of the artificial reef, in addition to its location on a muddy, silty substrate, resulted in a constant cover of fine grain particles which presumably discouraged settlement of invertebrates and small cryptic fish species on the artificial reef.
Introduction The coral reefs of the Red Sea are considered to be among the most diverse and exquisite of the IndoPacific zoogeographical region (Loya 1972). As a result of increased urbanization and coastal development in various parts of the Gulf of Elat (= Gulf of Aqaba), there is mounting anthropogenic pressure on the local coastal habitats, degradation of sea grass beds, coral breakage, algal overgrowth and regression of mangrove stands (Aleem 1990, Riegl & Velimirov 1991, Hawkins & Roberts 1994, Frihy et al. 1996, Stone et al. 1996). The process of continuing deterioration of the coastal habitat near Elat has become an important issue, among other things, due to the highly developed local tourist industry (Riegl & Velimirov 1991). Although no conclusive evidence is available as to the precise cause, the decline of the natural reef habitat in Elat is assumed to be the result of a long history of phosphate and oil pollution, raw sewage effluents, coastal siltation and
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EBFI 1915
land runoff, large-scale recreational tourism, extensive scuba diving activity and, most recently, the addition of mariculture net pens.1,2,3,4
1 Diamant, A. & O. Zmora. 1995. The problem of Eilat’s sewage disposal as a public issue. Proc. Ecosystem of the Gulf of Aqaba in Relation to the Enhanced Economical Development and the Peace Process – II. Eilat, 30 Jan–2 Feb 1995. pp. 63–66. 2 Furman, N. 1995. Correlation of diving activity and skeletal breakage in reef invertebrates pp. 27–28. In: The Ecosystem of the Gulf of Aqaba in Relation to the Enhanced Economical Development and the Peace Process – II, 30 Jan–2 Feb 1995 (Abstract). 3 Golani, D. 1996. Recruitment and fish community in the arti-
ficial reef in the Gulf of Eilat. Proc. Ecosystem of the Gulf of Aqaba in Relation to the Enhanced Economical Development and the Peace Process – III, Eilat, 22–25 Jan 1996, p. 46. 4 Popper, D. 1995. Expected impact of cage culture in the Gulf of Eilat. Proc. Ecosystem of the Gulf of Aqaba in Relation to the Enhanced Economical Development and the Peace Process – II, Eilat, 30 Jan–2 Feb 1995, pp. 72–77.
PIPS 188564
276 Planned construction of artificial reefs is now a routine practice throughout the world (Bohnsack et al. 1991, Grossman et al. 1997, Pickering & Whitmarsh 1997). Artificial reefs are thought to enhance low productivity ecosystems by attracting valuable commercial fish species, to rehabilitate damaged coastal ecosystems by providing new substrate for settlement and recruitment of aquatic fauna and flora, and to create attractive new sites for recreational fishing and/or sport diving (Caley & Stjohn 1996). In view of the regression of coral reefs and associated coastal habitats in the northern Red Sea, there is a growing interest in artificial reefs in Elat, and several projects have been carried out in recent years to create new underwater attractions for divers with the primary objective of easing the pressure on the heavily dived natural coral reefs. The only available published report on coral reef fish communities around artificial structures for this region is an abstract on the fish community around steel columns of oil jetties in Elat’s ‘Katza’ Oil Port (Rilov & Benayahu 1994). These authors mentioned 149 fish species belonging to 35 families from the site, but a detailed list was not given. Two additional studies which are relevant were carried out in the Gulf of Elat and have documented the successive development of fish communities on defaunated natural reefs. Gundermann & Popper (1975) investigated the results of an accidental chemical poisoning of a fish community and found a complete recovery of the fish populations after 10–12 months. Another study near Nuweiba, Egypt (60 km south of Elat) by Ben-Tuvia et al. (1983) analyzed the decrease of fish community on three shallow water habitats and their subsequent re-colonization. Both studies indicated that re-colonization of fishes in disrupted Red Sea coastal habitats is a rapid process. The present study is the first attempt to monitor fish colonization patterns of newly established artificial substrates in the Red Sea. In the present paper we report on the colonization of such fishes over a period of 728 days.
Figure 1. Map of study site. A1–A4 = amphibian vehicles, B = circular bellow, C1–C2 = metal construction beams, HE = heat exchanger unit, R = steam roller.
Materials and methods
natural reef (Figure 1). The artificial reef consisted of seven metal structures: a circular bellows with a radius of 2.4 m and 1 m in height; a cylinder shaped heat exchanger unit 0.9 m in diameter and 5.4 m in length and containing numerous 2.5 cm pipes bundled together, two metal construction beams 11 m in length and 2.3 m in width and height, and four amphibian vehicles, each 9.5 m long, 2.3 m wide and 1.5 m high. Two of the latter were abutting, so that they could in effect be regarded as a single object. In addition, a steam roller was positioned nearby on the damaged coral reef bottom. This object, although monitored throughout the study, was not considered an integral part of the artificial reef due to the difficulty of distinguishing the associated fish community from that of the underlying and surrounding natural reef.
Study site
Censuses
The study site was located at the northern tip of the Gulf of Elat at 29◦ 320 8500 N, 34◦ 570 4700 E. The reef structure was placed on a flat, sandy bottom, approximately 300 m offshore at a depth of 22–24 m, and a distance of 20–50 m from an existing severely damaged
The artificial reef was established on 22 May 1991. The first census was carried out two days later. Subsequently, censuses were taken at approximately monthly intervals over the first year. In the second year, censuses were conducted approximately every two months. All
277 censuses were conducted with SCUBA and their duration was 25–30 min per dive. Fish individuals of each species were identified, counted and recorded for each separate reef component on plastic slates. In cases where fish could not be positively identified, they were recorded to the lowest possible taxonomic level (genus or family) and treated as distinct taxons. To decrease variations between censuses, resulting from personal bias of each counting diver (see Jennings & Polunin 1995) or temporal shifts in abundance, all of the censuses were carried out by the authors during the same time of day (10:30–12:30 h). Analysis The species diversity index was calculated according to Shannon & Weaver (1962): X ln Pi , H 0 = −Pi where Pi is the numerical proportion of the ith species from a given census. The turnover index, which expresses the change in species per consecutive censuses was calculated by using a modification of the index proposed by Talbot et al. (1978): g d + , Tov = 0.5 Nj Nk where d is the number of species lost since the earlier census, g is the number of species gained in the later census, Nj is the number of species in the earlier census and Nk is the number of species in the later census. The degree of similarity between fish communities was estimated by means of the Jaccard coefficient of community, S (Jaccard, 1912): S=
c , a+b−c
where a and b are the numbers of species in communities a and b, respectively, and c is the number of species shared by both. Results A total of 80 species belonging to 29 families was recorded in the combined censuses. An additional 14 species were recorded only from the steam roller. A list of the relative abundance and resident status of all observed species is given in Table 1.
The number of species and abundances of the recorded fish increased sharply during the first four months of the study, peaking at 34 species and 727 individuals (Figure 2). Subsequently, from day 155 onwards the number of individuals observed per census decreased to 200–400. The total, cumulative number of species observed during the first seven months rapidly increased, reaching 72 species at 116 days and leveling off, with an accretion of no more than two species per each subsequent census (Figure 3). The computed values of ‘species diversity’ and ‘species turnover’ are given in Table 2. The species diversity of the initial 7 censuses was compared to that of the subsequent 9 censuses. This partition of the study into two unequal segments was based on the a posteriori observation that the colonization curve exhibits two distinct phases: one of initial rapid build-up of the fish community and a second phase where the community reaches a plateau (see Figure 3). Analysis of the species diversity in the two phases indicated a significantly lower diversity in the initial phase (t-test, unequal variance assumed; t7 = 2.422; 0.01 < p < 0.02) (Sokal & Rohlf 1981). A comparison between the number of species and individuals on the two abutting amphibian vehicles with the two identical but separately placed vehicles is shown in Figure 4. There was a small difference between the two sites. With regard to the number of species the single vehicles had a mean higher number of species by 0.75 species, but this was found insignificant (t-test for paired comparison, t15 = 0.8364; 0.20 < p < 0.25). The number of individuals was higher on the abutting vehicles by 14.8 individuals, and this was also found insignificant (t15 = 0.8472; 0.20 < p < 0.25) (Sokal & Rohlf 1981). We observed different patterns of settlement and colonization in the reef’s dominant species (Figure 5). The domino dascyllus, Dascyllus trimaculatus, was overall the most dominant and constant species. From the second census (day 32) on, it appeared in large numbers of mainly adult individuals. The total number remained fairly constant between censuses, although alternating between the different metal objects that comprised the reef. Three fish species were characteristically associated with the highly complex heat exchange unit. Both grouper species Cephalopholis hemistiktos and Epinephelus fasciatus were represented at this site as large juveniles. Their numbers peaked after 8–9 months, remained constant for an additional 5–6 months and finally decreased; C. hemistiktos disappeared shortly afterwards. The third species,
278 Table 1. List of fish species observed on the artificial reef. Family
Species
AB
R.S.
Muraenidae
Gymnothorax javenicus (Bleeker, 1859) Gymnothorax nudivomer (Playfair & G¨unther, 1867) Siderea grisea (Lacep`ede, 1803) Synodus variegatus (Lac`epede, 1803) Antennarius sp. Fistularia commersoni R¨uppell, 1838 Neoniphon sammara (Forssk˚al, 1775) Sargocentron diadema (Lacep`ede, 1802) Pterois miles (Bennett, 1828) Pterois radiata (Cuvier, 1829)∗ Scorpaenopsis sp. Inimicus filamentosus (Cuvier, 1829) Synanceia verrucosa Bloch & Schneider, 1801 Papilloculiceps longiceps (Cuvier, 1829) Sorsogona prionota (Sauvage, 1873) Pseudanthias squamipinnis (Peters, 1855) Pseudanthias taeniatus (Klunzinger, 1884)∗ Cephalopholis hemistiktos (R¨uppell, 1830) Cephalopholis miniata (Forssk˚al, 1775)∗ Ephinephelus fasciatus (Forssk˚al, 1775) Pseudochromis flavivertex (R¨uppell, 1853) Priacanthus hamrur (Forssk˚all, 1775) Apogon annularis R¨uppell, 1829 Apogon cynosoma Bleeker, 1853 Cheilodipterus bipunctatus (Lachner, 1951) Cheilodipterus lineatus Lacep`ede, 1801 Cheilodipterus quinquelineatus Cuvier, 1828∗ Monotaxis grandoculis (Forssk˚al, 1775) Caesio suevicus Klunzinger, 1884 Pterocaesio chrysozona (Cuvier & Valenciennes, 1830) Plectorhynchus gaterinus (Forssk˚al, 1775) Plectorhynchus pictus (Thunberg, 1792) Plectorhynchus schotaf (Forssk˚al, 1775) Scolopsis ghanam (Forssk˚al, 1775) Mulloiedes flavolineatus (Lacep`ede, 1801) Parupeneus cyclostomus (Lacep`ede, 1801) Parupeneus forsskali Fourmanoir & Gu´ez´e, 1976 Parupeneus macronema (Lacep`ede, 1801) Parupeneus rubescens (Lacep`ede, 1801) Chaetodon austriacus R¨uppell, 1836∗ Chaetodon paucifasciatus Ahl, 1923 Heniochus diphreutes Jordan, 1903 Heniochus intermedius Steindachner, 1893 Amblyglyphydodon leucogaster (Bleeker, 1847) Amphiprion bicinctus R¨uppell, 1830∗ Chrysioptera unimaculata (Cuvier & Valenciennes, 1830) Dascyllus trimaculatus (R¨uppell, 1829) Neopomacentrus miryae Dor & Allen, 1977 Paraglyphidodon melas (Cuvier, 1830) Pomacentrus trichurus Playfair & G¨unther, 1866 Pomacentrid Apolemichthys xanthotis (Fraser-Brunner, 1951) Ganicanthus caudovittatus (G¨unther, 1860) Pomacanthus imperator (Bloch, 1787)
+ + +++ + + + + ++ +
R R R R R T R R R
+ + + + + ++
R R R R I R
+++
R
+++ + + + + + +
R R R R R R R
++ + + ++ + ++ ++ ++ + +++ ++ +
T T T R+T T T R+T I I R+T T T
+++ ++ ++ +
R T T R
+ +++ ++ + +++ + + ++ +
R R R R R R T T R
Synodontidae Antennariidae Fistularida Holocentridae Scorpaenidae
Synanceidae Platycephalidae Anthidae Serranidae
Pseudochromidae Priacanthidae Apogonidae
Lethrinidae Caesionidae Haemulidae
Nemipteridae Mullidae
Chaetodontidae
Pomacentridae
Pomacanthidae
279 Table 1. (Continued) Labridae
Scaridae
Blennidae
Gobiidae Acanthuridae Siganidae
Balistidae Ostraciidae Tetraodontidae
Diodontidae
Bodianus anthioides (Bennet, 1831) Bodianus axillaris (Bennet, 1831)∗ Cheilinus diagrammus (Lacep`ede, 1802) Cheilinus mentalis R¨uppell, 1828 Coris aygula Lacep`ede, 1802 Coris caudimacula (Quoy & Gaimard, 1834) Coris gaimard (Quoy & Gaimard, 1824) Halichoeres marginatus R¨uppell, 1835 Labroides dimidiatus (Valenciennes, 1839) Macropharyngodon bipartitus Smith, 1957∗ Paracheilinus octotaenia Fourmanoir, 1955 Pseudocheilinus evanidus Jordan & Evermann, 1903 Stethojulis interrupta (Bleeker, 1851) Thalassoma lunare (Linnaeus, 1758) Labrid sp. 1 Labrid sp. 2 Labrid sp. 3∗ Scarus sordidus Forssk˚al, 1775 Scarid sp. 1 Scarid sp. 2∗ Ecsenius aroni Springer, 1971∗ Ecsenius gravieri (Pellegrin, 1906) Plagiotremus tapeinosoma (Bleeker, 1857) Blennid sp. Gobiid sp. Acanthurus nigrofuscus (Forssk˚al, 1775)∗ Zebrasoma xanthurum (Blyth, 1852)∗ Siganus argenteus (Quoy & Gaimard, 1825)∗ Siganus luridus (Cuvier, 1829) Siganus rivulatus (Forssk˚al, 1775) Sufflamen albicaudatus (R¨uppell, 1829) Ostracion cubicus Linnaeus, 1758 Amblyrhinchotes spinosissimus (Regan, 1908)∗ Arothron hispidus (Linnaeus, 1758) Arothron stellatus (Bloch & Schneider, 1801) Canthigaster coronata (Vaillant & Sauvage, 1875) Canthigaster margaritata (R¨uppell, 1829) Canthigaster pygmaea Allen & Randall, 1977 Chilomycterus spilostylus Leis & Randall, 1981 Diodon hysterix Linnaeus, 1758
+++
R
++ + + + + + +
R T T T T R R
+++ + + + + +
R R I R R R
+++ +
R R
+++ + ++ +
R I R R
+ ++ ++ ++
I I R+T R
+ + ++ + + ++ +
R+T R+T R R R R+T R+T
∗
– species seen around the steam roller only. AB = abundance, + = rare, ++ = prevalent, + + + = common. R.S. = residential status; I – incidental, R – resident, T – transient.
Paracheilinus octotaenia, appeared abruptly in a large school of juveniles on day 155, after which its numbers remained fairly constant until the beginning of the second year (day 379), after which its numbers were considerably lower. In the third census (23 September 1991) a school of ∼ = 200 Ecsenius gravieri was observed for the first time. This species maintained large numbers of individuals for one year and then declined. It should be noted that underwater identification of this species
is problematic, since it bears close resemblance to two other species, Meiacanthus nigrolineatus and Plagiotremus townsendi. All three species form a Mullerian mimicry complex (Smith-Vaniz 1976). However, the latter two species were not observed during the study. Large schools of juveniles of two gregarious species, the scalefin anthias, Pseudanthias squamipinnis, and Miry’s damselfish, Neopomacentrus miryae, were initially observed on day 116, after which they declined
280
Figure 2. Change in the number of observed fish species (◦) and individuals (•) throughout the study.
Figure 3. Cumulative number of fish species. Figure 4. Comparison of the number of species and individuals between two adjacent amphibians vehicles (◦) and the two separate vehicles (•). Table 2. ‘Species diversity’ and ‘turnover index’ values calculated throughout the study. Date
No. of days
Species diversity
Turnover index
26 Jun 1991 26 Jul 1991 23 Sep 1991 1 Nov 1991 29 Nov 1991 8 Jan 1992 7 Feb 1992 28 Feb 1992 26 Mar 1992 1 May 1992 12 Jun 1992 13 Aug 1992 16 Oct 1992 11 Dec 1992 12 Mar 1993 29 May 1993
32 62 116 155 183 226 254 275 302 337 379 442 500 560 651 728
1.062 2.248 2.210 2.243 1.995 1.951 2.659 2.552 2.471 2.404 2.359 2.829 2.735 2.267 2.610 2.515
— 0.456 0.533 0.467 0.329 0.431 0.330 0.351 0.230 0.255 0.321 0.417 0.364 0.358 0.382 0.344 Figure 5. Changes in numbers of individuals of nine common fish species observed on the artificial reef throughout the study.
sharply or disappeared altogether. Both species reappeared in large numbers towards the end of the study period. Forsskal’s goatfish, Parupeneus forsskali, was classified as a ‘visitor’ member of the artificial reef fish community and appeared in fairly constant numbers on the sandy bottom adjacent to the reef.
Discussion The pattern of fish colonization of the Elat artificial reef displayed an initial rapid increase in the settlement in the first three to five months, followed by moderate
281 decline and leveling off. A high similarity between the fish communities was found upon comparison between the Elat artificial reef fish and Sinai, Red Sea coral reef (Ben-Tuvia et al. 1983) and the Sudan coast, Red Sea (Edwards & Rosewell 1981). Thirty three fish species (35.1%) were shared between the visual censuses in the present study and Nueiba, Red Sea (Ben Tuvia et al. 1983), while only 20 (21.3%) were shared with the Sudan coast, Red Sea (Edwards & Rosewell 1981). In terms of similarity between the fish communities, the Jaccard coefficient of community was 0.246 for ElatNueiba sites and 0.141 for the Eilat-Sudan coast sites. Species diversity was low in the first 7 months, which coincided with the larger number of individuals. Later on, when the school size of some of the species declined, but the number of species remained relatively stable, the diversity increase was statistically significant. The turnover index remained fairly constant throughout the study period, with values of 0.230– 0.533. Many of the fish species that formed the artificial reef community were clearly recruited from adjacent natural reef habitats. A notable example is the rapid appearance of adult crown butterflyfish, Chaetodon paucifasciatus, and the domino damselfish, Dascyllus trimaculatus, just a few days after the reef’s establishment. Larvae of these two species, like many other reef fish (Leis 1993) would have been unable to successfully settle in the artificial reef as metamorphosed juneviles, since they typically require a high complexity habitat (e.g. with thick vegetation), which was largely unavailable in the studied reef. Notwithstanding, some species, such as Pseudocheilinus octotaenia, Pseudanthias squamipinnis, Neopomacentrus myriae and two species of Cheilodipterus appeared only as juveniles. It is reasonable to assume that these were exceptions that were planktonic recruits, rather than displaced from a nearby reef. All of these species utilize characteristic niches that were available at certain sites on the artificial reef, such as a small seagrass bed, P. octotaenia, long spine sea urchins Diadema setosum (Cheilodipterus spp.) or crevice shelters for water column species (A. squamipinnis, N. myriae). The relationship between artificial reef size and dimensions of fish communities and their structure were studied by Ogden & Ebersole (1981) and Bortone & Kimmel (1991). In general, small reefs are characterized by a proportionally higher abundance and a community that is more diverse than that of large reefs, and this was explained as due to the higher ratio between
reef volume and available surface area (Russell 1975, Bohnsack et al. 1991). The structure of the presently studied reef, with its two connected amphibian vehicles and two identical but separate vehicles, provided us with an opportunity to examine such a relationship. As seen in Figure 4, no significant difference was noted: both the separate and combined objects showed a great variability between censuses and similar trends in the change in the number of individuals and species with time. This result may be explained by the relative large size of the compared objects, which may exceed the maximum reef size for which variability may be detected. Invertebrate settlement was slow and of poor diversity, compared to similar studies from other tropical regions (Golani 1996), and potentially delayed the settlement of cryptic fish species dependent on invertebrates as shelter. The lag in invertebrate settlement in the studied reef is believed to be the result of several factors (Golani 1996). Briefly, most of the artificial reef components were of low complexity, lacking cracks and crevices necessary for successful settlement of many invertebrate species. Secondly, the reef was situated on a fine silty substrate in an area of incessant turbidity, particularly in the 1–1.5 m overlying the bottom. The relatively low profile reef objects were thus perpetually enshrouded in silt particles, which probably discouraged invertebrate settlement. An adjacent area of tall underwater metal sculptures extending 8– 10 m above the bottom rapidly became encrusted with a diverse sessile invertebrate community species, probably because it was less prone to sedimentation and above the turbidity zone (see Diamant 1996). Unfortunately, there are no data available on the fish community which developed on these sculptures. The cause of degradation of the natural reef in the study area has yet to be determined. Since this site is deep and rather distant from shore, it is unlikely that the natural reef was damaged by scuba divers. It has been suggested that the growing area covered by fine silt in the northern tip of the Gulf of Elat is a result of the constant flow of the nutrient rich local urban sewage (Figure 1). This long-standing effluent may well be the primary cause of the destruction of the natural reef in the study area (Fishelson 1995). It is noteworthy that the oceanographic conditions that prevailed in the Gulf of Elat during the winter of 1992, during which part of this study was conducted, were exceptional. The surface water temperatures were lower by 1–2◦ C than the annual mean, causing a deeper
282 than normal vertical mixing of the water column and enhanced nutrient enrichment, which led to phytoplankton blooms, decreased visibility and exorbitant algae cover of hard substrates in the Gulf (Genin et al. 1995). Acknowledgements We are indebted to U. Motro for his advice and help with the statistical analyses. We thank U. Erel, Director General of the Elat Foreshore Authority, for his encouragement and support and S. Taggar, Eilat Municipality, for his inspiration. The logistic assistance of the Eilat Sailing Club and the numerous diving buddies who joined in and helped out with the field work is gratefully acknowledged. This study was supported by a grant from the Israel Ministry of Tourism. References cited Abu Aisha, K.M., I.A. Kobbia, M.S. El-Abyad, E.F. Shabana & F. Schanz. 1995. Impact of phosphorus loadings on macroalgal communities in the Red Sea coast of Egypt. Water, Air, Soil Pollution 83: 285–297. Aleem, A.A. 1990. Impact of human activity on marine habitats along the Red Sea coast of Saudi Arabia. Hydrobiologia 208: 7–15. Ben-Tuvia, A., A. Diamant, A. Baranes & D. Golani. 1983. Analysis of a coral reef fish community in shallow waters of Nuweiba, Gulf of Aqaba, Red Sea. pp. 193–206. In: M.F. Thompson (ed.) Conference Mar. Sci. Red Sea. Inst. Ocean. Fish., Cairo. Bohnsack, J.A., D.L. Johnson & R.F. Ambrose. 1991. Ecology of artificial reef habitats and fishes. pp. 61–107. In: W. Seaman & L.M. Sprague (ed.) Artificial Habitats for Marine and Freshwater Fisheries, Academic Press, San Diego. Bortone, S.A. & J.J. Kimmel. 1991. Environmental assessment and monitoring of artificial habitats. pp. 177–236. In: W. Seaman & L.M. Sprague (ed.) Artificial Habitats for Marine and Freshwater Fisheries, Academic Press, San Diego. Caley, M.J. & J. Stjohn. 1996. Refuge availability structures assemblages of tropical reef fishes. J. Anim. Ecol. 65: 414– 428. Edwards, A. & J. Rosewell. 1981. Vertical zonation of coral reef fishes in the Sudanese Red Sea. Hydrobiologia 79: 21–31. El Rayis, O.A. 1991. Ultraviolet absorption measurement as a rapid tool for tracing dispersion of sewage effluent and for classification of water masses in two Red Sea coastal lagoons, Jeddah. Bull. Nat. Inst. Oceanogr. Fish. Egypt 16: 131–147. Fishelson, L. 1995. Elat (Gulf of Aqaba) littoral: life on the red line of biodegradation. Isr. J. Zool. 41: 43–55.
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