Fish Colonization of an Artificial Reef in the Gulf of Elat, Northern Red

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 a 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]) 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 land runoff, large-scale recreational tourism, extensive scuba diving activity and, most recently, the addition ; ; ; The coral reefs of the Red Sea are considered to be of mariculture net pens.1 2 3 4 among the most diverse and exquisite of the Indo- Pacific zoogeographical region (Loya 1972). As a result of increased urbanization and coastal development in 1 = Diamant, A. & O. Zmora. 1995. The problem of Eilat’s various parts of the Gulf of Elat ( Gulf of Aqaba), sewage disposal as a public issue. Proc. Ecosystem of the Gulf there is mounting anthropogenic pressure on the local of Aqaba in Relation to the Enhanced Economical Development coastal habitats, degradation of sea grass beds, coral and the Peace Process – II. Eilat, 30 Jan–2 Feb 1995. pp. 63–66. breakage, algal overgrowth and regression of man- 2Furman, N. 1995. Correlation of diving activity and skeletal grove stands (Aleem 1990, Riegl & Velimirov 1991, breakage in reef invertebrates pp. 27–28. In: The Ecosystem of Hawkins & Roberts 1994, Frihy et al. 1996, Stone et al. the Gulf of Aqaba in Relation to the Enhanced Economical Devel- 1996). The process of continuing deterioration of the opment and the Peace Process – II, 30 Jan–2 Feb 1995 (Abstract). coastal habitat near Elat has become an important issue, 3Golani, D. 1996. Recruitment and fish community in the arti- among other things, due to the highly developed local ficial reef in the Gulf of Eilat. Proc. Ecosystem of the Gulf of Aqaba in Relation to the Enhanced Economical Development and tourist industry (Riegl & Velimirov 1991). Although no the Peace Process – III, Eilat, 22–25 Jan 1996, p. 46. conclusive evidence is available as to the precise cause, 4Popper, D. 1995. Expected impact of cage culture in the Gulf the decline of the natural reef habitat in Elat is assumed of Eilat. Proc. Ecosystem of the Gulf of Aqaba in Relation to the to be the result of a long history of phosphate and oil Enhanced Economical Development and the Peace Process – II, pollution, raw sewage effluents, coastal siltation and Eilat, 30 Jan–2 Feb 1995, pp. 72–77. DISK EBFI 1915 PIPS 188564 276 Planned construction of artificial reefs is now a rou- tine 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 com- mercial 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 men- tioned 149 fish species belonging to 35 families from = the site, but a detailed list was not given. Figure 1. Map of study site. A1–A4 amphibian vehicles, B = circular bellow, C1–C2 = metal construction beams, HE = Two additional studies which are relevant were car- heat exchanger unit, R = steam roller. ried out in the Gulf of Elat and have documented the successive development of fish communities on defau- nated natural reefs. Gundermann & Popper (1975) natural reef (Figure 1). The artificial reef consisted investigated the results of an accidental chemical poi- of seven metal structures: a circular bellows with a soning of a fish community and found a complete radius of 2.4 m and 1 m in height; a cylinder shaped recovery of the fish populations after 10–12 months. heat exchanger unit 0.9 m in diameter and 5.4 m in Another study near Nuweiba, Egypt (60 km south of length and containing numerous 2.5 cm pipes bundled Elat) by Ben-Tuvia et al. (1983) analyzed the decrease together, two metal construction beams 11 m in length of fish community on three shallow water habitats and and 2.3 m in width and height, and four amphibian vehi- their subsequent re-colonization. Both studies indi- cles, each 9.5 m long, 2.3 m wide and 1.5 m high. Two cated that re-colonization of fishes in disrupted Red Sea of the latter were abutting, so that they could in effect be coastal habitats is a rapid process. The present study is regarded as a single object. In addition, a steam roller the first attempt to monitor fish colonization patterns of was positioned nearby on the damaged coral reef bot- newly established artificial substrates in the Red Sea. tom. This object, although monitored throughout the In the present paper we report on the colonization of study, was not considered an integral part of the arti- such fishes over a period of 728 days. ficial reef due to the difficulty of distinguishing the associated fish community from that of the underlying Materials and methods and surrounding natural reef. Study site Censuses The study site was located at the northern tip of the The artificial reef was established on 22 May 1991. Gulf of Elat at 29◦3208500N, 34◦5704700E. The reef The first census was carried out two days later. Subse- structure was placed on a flat, sandy bottom, approxi- quently, censuses were taken at approximately monthly mately 300 m offshore at a depth of 22–24 m, and a dis- intervals over the first year. In the second year, censuses tance of 20–50 m from an existing severely damaged were conducted approximately every two months. All 277 censuses were conducted with SCUBA and their dura- The number of species and abundances of the tion was 25–30 min per dive. Fish individuals of each recorded fish increased sharply during the first four species were identified, counted and recorded for each months of the study, peaking at 34 species and 727 separate reef component on plastic slates. In cases individuals (Figure 2). Subsequently, from day 155 where fish could not be positively identified, they were onwards the number of individuals observed per census recorded to the lowest possible taxonomic level (genus decreased to 200–400. The total, cumulative number of or family) and treated as distinct taxons. To decrease species observed during the first seven months rapidly variations between censuses, resulting from personal increased, reaching 72 species at 116 days and level- bias of each counting diver (see Jennings & Polunin ing off, with an accretion of no more than two species 1995) or temporal shifts in abundance, all of the cen- per each subsequent census (Figure 3). The computed suses were carried out by the authors during the same values of ‘species diversity’ and ‘species turnover’ are time of day (10:30–12:30 h). given in Table 2. The species diversity of the initial 7 censuses was compared to that of the subsequent 9 Analysis censuses. This partition of the study into two unequal segments was based on the a posteriori observation that The species diversity index was calculated according the colonization curve exhibits two distinct phases: one to Shannon & Weaver (1962): of initial rapid build-up of the fish community and a X second phase where the community reaches a plateau 0 H =−Pi ln Pi; (see Figure 3). Analysis of the species diversity in the two phases indicated a significantly lower diversity where Pi is the numerical proportion of the ith in the initial phase (t-test, unequal variance assumed; species from a given census. The turnover index, which t7 = 2:422; 0:01 < p < 0:02) (Sokal & Rohlf 1981). expresses the change in species per consecutive cen- A comparison between the number of species and suses was calculated by using a modification of the individuals on the two abutting amphibian vehicles index proposed by Talbot et al.

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