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

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. (1978): with the two identical but separately placed vehicles is shown in Figure 4. There was a small difference d g between the two sites. With regard to the number of Tov = 0.5 + , Nj Nk species the single vehicles had a mean higher number of species by 0.75 species, but this was found insignif- d where is the number of species lost since the ear- icant (t-test for paired comparison, t15 = 0.8364; lier census, g is the number of species gained in the 0.20 < p < 0.25). The number of individuals was later census, Nj is the number of species in the earlier higher on the abutting vehicles by 14.8 individuals, N census and k is the number of species in the later cen- and this was also found insignificant (t15 = 0.8472; sus. The degree of similarity between fish communities 0.20 < p < 0.25) (Sokal & Rohlf 1981). was estimated by means of the Jaccard coefficient of We observed different patterns of settlement and col- community, S (Jaccard, 1912): onization in the reef’s dominant species (Figure 5). The c domino dascyllus, Dascyllus trimaculatus, was overall S = , the most dominant and constant species. From the sec- a + b − c ond census (day 32) on, it appeared in large numbers where a and b are the numbers of species in communi- of mainly adult individuals. The total number remained ties a and b, respectively, and c is the number of species fairly constant between censuses, although alternating shared by both. between the different metal objects that comprised the reef. Three fish species were characteristically Results associated with the highly complex heat exchange unit. Both grouper species Cephalopholis hemistik- A total of 80 species belonging to 29 families was tos and Epinephelus fasciatus were represented at recorded in the combined censuses. An additional 14 this site as large juveniles. Their numbers peaked species were recorded only from the steam roller. A after 8–9 months, remained constant for an addi- list of the relative abundance and resident status of all tional 5–6 months and finally decreased; C. hemistik- observed species is given in Table 1. tos 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) + R Gymnothorax nudivomer (Playfair & Gunther,¨ 1867) + R Siderea grisea (Lacepede,` 1803) +++ R Synodontidae Synodus variegatus (Lacepede,` 1803) + R Antennariidae Antennarius sp. + R Fistularida Fistularia commersoni Ruppell,¨ 1838 + T Holocentridae Neoniphon sammara (Forsskal,˚ 1775) + R Sargocentron diadema (Lacepede,` 1802) ++ R Scorpaenidae Pterois miles (Bennett, 1828) + R Pterois radiata (Cuvier, 1829)∗ Scorpaenopsis sp. + R Synanceidae Inimicus filamentosus (Cuvier, 1829) + R Synanceia verrucosa Bloch & Schneider, 1801 + R Platycephalidae Papilloculiceps longiceps (Cuvier, 1829) + R Sorsogona prionota (Sauvage, 1873) + I Anthidae Pseudanthias squamipinnis (Peters, 1855) ++ R Pseudanthias taeniatus (Klunzinger, 1884)∗ Serranidae Cephalopholis hemistiktos (Ruppell,¨ 1830) +++ R Cephalopholis miniata (Forsskal,˚ 1775)∗ Ephinephelus fasciatus (Forsskal,˚ 1775) +++ R Pseudochromidae Pseudochromis flavivertex (Ruppell,¨ 1853) + R Priacanthidae Priacanthus hamrur (Forsskall,˚ 1775) + R Apogonidae Apogon annularis Ruppell,¨ 1829 + R Apogon cynosoma Bleeker, 1853 + R Cheilodipterus bipunctatus (Lachner, 1951) + R Cheilodipterus lineatus Lacepede,` 1801 + R Cheilodipterus quinquelineatus Cuvier, 1828∗ Lethrinidae Monotaxis grandoculis (Forsskal,˚ 1775) ++ T Caesionidae Caesio suevicus Klunzinger, 1884 + T Pterocaesio chrysozona (Cuvier & Valenciennes, 1830) + T Haemulidae Plectorhynchus gaterinus (Forsskal,˚ 1775) ++ R + T Plectorhynchus pictus (Thunberg, 1792) + T Plectorhynchus schotaf (Forsskal,˚ 1775) ++ T Nemipteridae Scolopsis ghanam (Forsskal,˚ 1775) ++ R + T Mullidae Mulloiedes flavolineatus (Lacepede,` 1801) ++ I Parupeneus cyclostomus (Lacepede,` 1801) + I Parupeneus forsskali Fourmanoir & Guez´ e,´ 1976 +++ R+T Parupeneus macronema (Lacepede,` 1801) ++ T Parupeneus rubescens (Lacepede,` 1801) + T Chaetodontidae Chaetodon austriacus Ruppell,¨ 1836∗ Chaetodon paucifasciatus Ahl, 1923 +++ R Heniochus diphreutes Jordan, 1903 ++ T Heniochus intermedius Steindachner, 1893 ++ T Pomacentridae Amblyglyphydodon leucogaster (Bleeker, 1847) + R Amphiprion bicinctus Ruppell,¨ 1830∗ Chrysioptera unimaculata (Cuvier & Valenciennes, 1830) + R Dascyllus trimaculatus (Ruppell,¨ 1829) +++ R Neopomacentrus miryae Dor & Allen, 1977 ++ R Paraglyphidodon melas (Cuvier, 1830) + R Pomacentrus trichurus Playfair & Gunther,¨ 1866 +++ R Pomacentrid + R Pomacanthidae Apolemichthys xanthotis (Fraser-Brunner, 1951) + T Ganicanthus caudovittatus (Gunther,¨ 1860) ++ T Pomacanthus imperator (Bloch, 1787) + R 279

Table 1.(Continued)

Labridae Bodianus anthioides (Bennet, 1831) +++ R Bodianus axillaris (Bennet, 1831)∗ Cheilinus diagrammus (Lacepede,` 1802) ++ R Cheilinus mentalis Ruppell,¨ 1828 + T Coris aygula Lacepede,` 1802 + T Coris caudimacula (Quoy & Gaimard, 1834) + T Coris gaimard (Quoy & Gaimard, 1824) + T Halichoeres marginatus Ruppell,¨ 1835 + R Labroides dimidiatus (Valenciennes, 1839) + R Macropharyngodon bipartitus Smith, 1957∗ Paracheilinus octotaenia Fourmanoir, 1955 +++ R Pseudocheilinus evanidus Jordan & Evermann, 1903 + R Stethojulis interrupta (Bleeker, 1851) + I Thalassoma lunare (Linnaeus, 1758) + R Labrid sp. 1 + R Labrid sp. 2 + R Labrid sp. 3∗ Scaridae Scarus sordidus Forsskal,˚ 1775 +++ R Scarid sp. 1 + R Scarid sp. 2∗ Blennidae Ecsenius aroni Springer, 1971∗ Ecsenius gravieri (Pellegrin, 1906) +++ R Plagiotremus tapeinosoma (Bleeker, 1857) + I Blennid sp. ++ R Gobiidae Gobiid sp. + R Acanthuridae Acanthurus nigrofuscus (Forsskal,˚ 1775)∗ Zebrasoma xanthurum (Blyth, 1852)∗ Siganidae Siganus argenteus (Quoy & Gaimard, 1825)∗ Siganus luridus (Cuvier, 1829) + I Siganus rivulatus (Forsskal,˚ 1775) ++ I Balistidae Sufﬂamen albicaudatus (Ruppell,¨ 1829) ++ R + T Ostraciidae Ostracion cubicus Linnaeus, 1758 ++ R Tetraodontidae Amblyrhinchotes spinosissimus (Regan, 1908)∗ Arothron hispidus (Linnaeus, 1758) + R + T Arothron stellatus (Bloch & Schneider, 1801) + R + T Canthigaster coronata (Vaillant & Sauvage, 1875) ++ R Canthigaster margaritata (Ruppell,¨ 1829) + R Canthigaster pygmaea Allen & Randall, 1977 + R Diodontidae Chilomycterus spilostylus Leis & Randall, 1981 ++ R + T Diodon hysterix Linnaeus, 1758 + 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 is problematic, since it bears close resemblance to school of juveniles on day 155, after which its num- two other species, Meiacanthus nigrolineatus and Pla- bers remained fairly constant until the beginning of the giotremus townsendi. All three species form a Mulle- second year (day 379), after which its numbers were rian mimicry complex (Smith-Vaniz 1976). However, considerably lower. the latter two species were not observed during the In the third census (23 September 1991) a school study. of =∼ 200 Ecsenius gravieri was observed for the first Large schools of juveniles of two gregarious species, time. This species maintained large numbers of indi- the scalefin anthias, Pseudanthias squamipinnis, and viduals for one year and then declined. It should be Miry’s damselfish, Neopomacentrus miryae, were ini- noted that underwater identification of this species tially 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 32 1.062 — 26 Jul 1991 62 2.248 0.456 23 Sep 1991 116 2.210 0.533 1 Nov 1991 155 2.243 0.467 29 Nov 1991 183 1.995 0.329 8 Jan 1992 226 1.951 0.431 7 Feb 1992 254 2.659 0.330 28 Feb 1992 275 2.552 0.351 26 Mar 1992 302 2.471 0.230 1 May 1992 337 2.404 0.255 12 Jun 1992 379 2.359 0.321 13 Aug 1992 442 2.829 0.417 16 Oct 1992 500 2.735 0.364 11 Dec 1992 560 2.267 0.358 12 Mar 1993 651 2.610 0.382 29 May 1993 728 2.515 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 reap- peared in large numbers towards the end of the study Discussion period. Forsskal’s goatfish, Parupeneus forsskali,was classified as a ‘visitor’ member of the artificial reef fish The pattern of fish colonization of the Elat artificial reef community and appeared in fairly constant numbers on displayed an initial rapid increase in the settlement in the sandy bottom adjacent to the reef. the first three to five months, followed by moderate 281 decline and leveling off. A high similarity between the reef volume and available surface area (Russell 1975, fish communities was found upon comparison between Bohnsack et al. 1991). The structure of the presently the Elat artificial reef fish and Sinai, Red Sea coral reef studied reef, with its two connected amphibian vehi- (Ben-Tuvia et al. 1983) and the Sudan coast, Red Sea cles and two identical but separate vehicles, provided (Edwards & Rosewell 1981). Thirty three fish species us with an opportunity to examine such a relation- (35.1%) were shared between the visual censuses in the ship. As seen in Figure 4, no significant difference was present study and Nueiba, Red Sea (Ben Tuvia et al. noted: both the separate and combined objects showed 1983), while only 20 (21.3%) were shared with the a great variability between censuses and similar trends Sudan coast, Red Sea (Edwards & Rosewell 1981). In in the change in the number of individuals and species terms of similarity between the fish communities, the with time. This result may be explained by the rel- Jaccard coefficient of community was 0.246 for Elat- ative large size of the compared objects, which may Nueiba sites and 0.141 for the Eilat-Sudan coast sites. exceed the maximum reef size for which variability Species diversity was low in the first 7 months, may be detected. which coincided with the larger number of individ- Invertebrate settlement was slow and of poor diver- uals. Later on, when the school size of some of the sity, compared to similar studies from other tropical species declined, but the number of species remained regions (Golani 1996), and potentially delayed the set- relatively stable, the diversity increase was statistically tlement of cryptic fish species dependent on inverte- significant. The turnover index remained fairly con- brates as shelter. The lag in invertebrate settlement in stant throughout the study period, with values of 0.230– the studied reef is believed to be the result of sev- 0.533. eral factors (Golani 1996). Briefly, most of the artifi- Many of the fish species that formed the artificial cial reef components were of low complexity, lacking reef community were clearly recruited from adjacent cracks and crevices necessary for successful settlement natural reef habitats. A notable example is the rapid of many invertebrate species. Secondly, the reef was appearance of adult crown butterflyfish, Chaetodon situated on a fine silty substrate in an area of incessant paucifasciatus, and the domino damselfish, Dascyllus turbidity, particularly in the 1–1.5 m overlying the bot- trimaculatus, just a few days after the reef’s establish- tom. The relatively low profile reef objects were thus ment. Larvae of these two species, like many other perpetually enshrouded in silt particles, which proba- reef fish (Leis 1993) would have been unable to suc- bly discouraged invertebrate settlement. An adjacent cessfully settle in the artificial reef as metamorphosed area of tall underwater metal sculptures extending 8– juneviles, since they typically require a high com- 10 m above the bottom rapidly became encrusted with a plexity habitat (e.g. with thick vegetation), which was diverse sessile invertebrate community species, prob- largely unavailable in the studied reef. Notwithstand- ably because it was less prone to sedimentation and ing, some species, such as Pseudocheilinus octotaenia, above the turbidity zone (see Diamant 1996). Unfortu- Pseudanthias squamipinnis, Neopomacentrus myriae nately, there are no data available on the fish community and two species of Cheilodipterus appeared only as which developed on these sculptures. juveniles. It is reasonable to assume that these were The cause of degradation of the natural reef in the exceptions that were planktonic recruits, rather than study area has yet to be determined. Since this site is displaced from a nearby reef. All of these species uti- deep and rather distant from shore, it is unlikely that the lize characteristic niches that were available at certain natural reef was damaged by scuba divers. It has been sites on the artificial reef, such as a small seagrass bed, suggested that the growing area covered by fine silt in P. octotaenia, long spine sea urchins Diadema seto- the northern tip of the Gulf of Elat is a result of the sum (Cheilodipterus spp.) or crevice shelters for water constant flow of the nutrient rich local urban sewage column species (A. squamipinnis, N. myriae). (Figure 1). This long-standing effluent may well be the The relationship between artificial reef size and primary cause of the destruction of the natural reef in dimensions of fish communities and their structure the study area (Fishelson 1995). were studied by Ogden & Ebersole (1981) and Bortone It is noteworthy that the oceanographic conditions & Kimmel (1991). In general, small reefs are character- that prevailed in the Gulf of Elat during the winter of ized by a proportionally higher abundance and a com- 1992, during which part of this study was conducted, munity that is more diverse than that of large reefs, and were exceptional. The surface water temperatures were this was explained as due to the higher ratio between lower by 1–2◦C than the annual mean, causing a deeper 282 than normal vertical mixing of the water column and Frihy, O.E., A.M. Fanos, A.A. Khafagy & K.A. 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