Introduction

A considerable number of studies have been carried out in Sharm Obhur of Jeddah. However, most of the research has focused on the impact of the municipal effluents in the water and has not assessed the impacts on the coral reef ecosystem (Basaham et al. 1999; El-Sayed and Niaz 1999; El Sayed 1999; El Sayed et al. 2002; Basaham 1998, 2004; Niaz and El-Sayed 2003; El Sayed and Basaham 2004). Behairy (1980) conducted preliminary investigations on heavy metals in the water, sediments and plankton in Sharm Obhur. They compared the concentrations of Cu, Cd, Zn, Mn and Fe in water, sediments and plankton of Sharm Obhur with those in other parts of the world. No significant pollution by heavy metals was detected. Later, in 1996, Fahmy and Saad studied the temporal and spatial distributions of heavy metals in both the surface water and plankton in Sharm Obhur. They revealed an increase in the concentration of heavy metals (Mn, Cu, Zn and Cd) in the creek water, which could pose a threat to the organisms in the area. A study on the vertical mixing of seawater in Sharm Obhur has reported that the creek receives approximately 1018 kg m−3 of discharge from the nearby resorts (Al-Subhi 2011).

There have been several studies on the coral reefs of Sharm Obhur. Coral transplantation has been studied by Al-Sofyani and Davies (1993). Physiological studies of two reef-building corals were carried out by Floos (2012) in the Sharm Obhur coral reefs. Al-Lihaibi et al. (1998) estimated the chemical compositions, i.e. amino acid and lipid concentrations, of three corals, namely, Stylophora pistillata, Lobophyllia corymbosa and Echinophora gemmacea, to determine their metabolic pathways in connection with their feeding behaviours. All the above studies have focused on various aspects of coral reefs, but studies on the biodiversity are lacking.

The expanding settlements and recreational activities at Sharm Obhur lead to the contamination of seawater, which affects coral growth and diversity. The abundance of soft corals in the creek area indicates the decline of scleractinian coral cover. Moreover, the influx of freshwater from stormwater drainage located on the eastern end of ‘Wadi Al Kura’ Creek not only brings more silt but also reduces the creek’s water quality.

Scleractinian corals play a vital role in coral reef formation. However, they are vulnerable to anthropogenic and natural influences (Riegl et al. 2012b; Furby et al. 2013). The coral reef ecosystems situated around Jeddah are degrading at an alarming rate due to local anthropogenic impacts (Ziegler et al. 2016). Hence, it is necessary to collect baseline data on these tropical ecosystems to periodically assess their health status. The taxonomic identification of the scleractinian corals on the Sharm Obhur coral reefs is urgently needed to prepare a list of the species currently present. Hence, this study aimed to assess the current status of the coral reefs of Sharm Obhur in Jeddah.

Materials and methods

Study area

Sharm Obhur is a narrow extension of a coastal water body (Creek) that is approximately 10 km long and 500 m wide, and is situated in the central part of the Red Sea. It is located approximately 35 km away from North Jeddah (21°42′11″–21°45′24″ N and 39°05′12″–39°08′48″ E). The maximum observed depth of Sharm Obhur (creek) is 40 m. The depth gradually decreases landward and reaches approximately 3 m at the head of the creek. The fringing reef pattern of the coast continues into the outer part of the creek. Sharm Obhur is known for its excellent coral cover, which attracts recreational activities. Thus, there are many resorts, hotels and dive centres in the area that could impose harm to the reef ecosystem.

Sampling

The study area was divided into three zones viz., Obhur Creek Entrance, Obhur Creek Centre and Storm Water Site. Among them, nine study sites (Fig. 1) were selected in Sharm Obhur to represent the entire creek. The sessile benthic community of the creek was biophysically assessed from November 2012 to December 2013 using the line intercept transect method (English et al. 1997). Similar biophysical status assessments of coral reef ecosystems have been carried out worldwide to estimate biodiversity patterns and growth forms (Riegl et al. 2012a; Riegl and Purkis 2012; Al-Sofyani et al. 2014). A 20-m-long flexible underwater transect tape was laid on the reefs roughly parallel to the shore, with five replicates at each site. The benthic community under the transition points was recorded on underwater slates using Global Coral Reef Monitoring Network (GCRMN) codes.

Fig. 1
figure 1

Map showing the study sites

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The scleractinian corals were classified into two major categories, namely, Acropora (AC) and non-Acropora (NAC), for better understanding. The acroporid corals were further divided into three groups according to their growth forms, namely, digitate (ACD), branching (ACB) and tabular (ACT). Similarly, the non-acroporid corals were also sub-categorised as massive coral (CM), branching coral (CB), encrusting coral (CE), foliose coral (CF) and mushroom coral (CMR), based on their growth forms.

The other principal associates were categorised as non-scleractinian corals, abiotic, algae, others and sponges. The non-scleractinian coral category includes Millepora (CME) and soft corals (SC), whereas the abiotic category includes dead coral with algae (DCA), rubble (R) and rock (RCK). The algae category covers all types of algae, such as coralline algae (including Halimeda), macroalgae and turf algae, and observations were grouped as an algal assemblage if they were found in groups. Sponges were denoted as SP. The ‘others’ category comprised the rest of the living organisms that are not listed above but were observed in the reef ecosystem, such as sea stars, sea cucumbers, giant clams and bivalves.

The percentage covers of scleractinian and non-scleractinian corals, the abiotic forms and the other associated organisms were estimated from the collected raw data using the AIMS Reef Monitoring Data Entry System (ARMDES 1996).

Species diversity was calculated according to Shannon and Weaver (1963):

$$ \mathrm{H}={\sum}_{i=1}^n pi\mathit{\ln} pi $$

where pi = n/N is the proportion of the number of individuals of species (n) to the total number of individuals (N).

Richness was calculated according to Margalef (1968):

$$ \mathrm{D}=\left(\mathrm{S}-\mathrm{I}\right)/\ln\ \mathrm{N} $$

where D = richness, S is the number of species and N is the total number of individuals.

Further statistical analyses, such as a principal component analysis (PCA), a metric multi-dimensional scaling (MDS) analysis (to identify the dominant coral growth forms as well as the species diversity with respect to the selected study sites), a Bray–Curtis cluster analysis (for similarity study) and species richness, were carried out using PRIMER 7 version 7.0.5 (Clarke and Gorley 2015) and PAST version 2.15 (Hammer 2012). The water quality of Sharm Obhur was estimated using portable water quality analysis equipment (Horiba 2010).

Results

The biophysical status of the benthic forms is presented in Fig. 2. The contribution of soft corals is a strong influence (Fig. 3), followed by the non-acroporid corals (PC1: 59.3% variance). Strong variability was found between the stormwater site and the rest of the study sites. The soft corals and non-acroporid corals seemed to be higher in the creek entrance, followed by the central creek and gradually decreased towards the storm-water site. Variables such as silt, sand, water, litter (abiotic), algal assemblage and rubble strongly dominate the stormwater discharge sites. The metric multi-dimensional scaling analysis of the life-form cover of Sharm Obhur depicted the formation of two clusters (Fig. 3a) with 85% similarity. One cluster included the entrance of the creek and the second one covered the central area of the creek. These two clusters are either unoccupied or restricted zones and, hence, possess excellent hard coral cover.

Fig. 2
figure 2

Biophysical status of the benthic forms and the coral biodiversity indices observed in the Obhur Creek, Red Sea. ACR acroporid corals; NAC non-acroporid corals; CMR mushroom coral; CME milleporid coral; SC soft coral; SP sponges; OT other associates; DCA dead coral with algae; R rubble; ABT abiotics (sand, silt and water column); AA algal assemblage; St site

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Fig. 3
figure 3

Multi-dimensional scaling (MDS) overlaid with the principal component analysis (PCA) of biophysical forms observed in the Obhur Creek, Red Sea. ACR acroporid corals; NAC non-acroporid corals; CMR mushroom coral; CME milleporid coral; SC soft coral; SP sponges, OT other associates; DCA dead coral with algae; R rubble; ABT abiotics (sand, silt and water column); AA algal assemblage; ACB Acropora branching; ACT Acropora tabular; CM massive coral; CB branching coral; CS sub-massive coral; CE encrusting coral; CF foliose coral; 1–9 sites

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Among the different growth forms of scleractinian corals, NAC dominated the Sharm Obhur coral reefs with 24.18% cover. Among the NAC forms, the massive corals Porites and Goniastrea were commonly found at Site 2 and Site 3. The metric MDS analysis (Fig. 3b) also indicated that the contribution of massive corals (CM) was more predominant at Sites 2 and 3. On the other hand, it revealed that the contributions of acroporid corals decreased from Site 2 to Site 7. Acroporid corals were observed on the reef crest and the reef slope of undisturbed areas, but with a limited mean cover. Encrusting corals were found to be dominant at Site 4 (16.55%). The other coral forms, such as branching (CB), sub-massive (CS), foliose (CF) and mushroom corals (CMR), were not commonly found at any of the study sites (Fig. 3b).

Overall, 19.66% of the creek was covered by DCA. Among the sites, the most DCA cover was noticed at Site 1 (39.15%), followed by Site 7 (22.50%). The MDS overlaid with the PCA also supported this finding (Fig. 3a). Similarly, a higher coverage of algal assemblages was found at Site 7, with a mean cover of 32.8%. Among the algal assemblages, turf algae alone contributed 28%. The suspended silt percentage was highest at Site 8 (25%), where the entire bottom was covered by mud derived from the Wadi Al Kura discharge (Fig. 3a). The overall sponge population in Sharm Obhur was observed as moderate in cover (3.6%). Among the sites, higher contributions of sponge cover were found at Site 1 (7.75%), followed by Site 7 (7.15%).

The species diversity indices are shown in Fig. 2b. Higher diversity indices were observed at Site 7, followed by Sites 2 and 1. The MDS overlaid with the PCA (Fig. 4) supported the findings that there were more species at Site 7, followed by Site 2. Similar to life-form cover, there was variability (PC1: 31.8% variance) between the stormwater site and the other sites based on the degree of coral diversity. Moreover, two clusters were formed with 45% similarity. Among these, one mixed cluster was formed between the entrance of the creek and the centre of the creek, and another one was formed at the entrance of the creek.

Fig. 4
figure 4

MDS overlaid with the PCA of species diversity observed in the Obhur Creek, Red Sea. PL Plerogyra sp.; PO Porites sp.; GS Gardineroseris sp.; EC Echinopora sp.; GO Goniastrea sp.; DI Diploastrea sp.; PT Platygyra sp.; FV Favites sp.; PP Pocillopora sp.; AS Astreopora sp.; MO Montipora sp.; FA Favia sp.; AC Acropora sp.; GA Galaxea sp.; LO Lobophyllia sp.; SE Seriatopora sp.; GP Goniopora sp.; LP Leptastrea sp.; PA Pachyseris sp.; ST Stylophora sp.; AL Alveopora sp.; MY Mycedium sp.; OX Oxypora sp.; TU Turbinaria sp.; PD Podabacia sp.; HE Herpolitha sp.; ST sites

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Sedimentation and nutrients

It was observed that the overall sedimentation rate (mg.cm−2 d−1) was alarming at Sharm Obhur. Although there is not much wave-induced turbulence, the drainage channels bring an enormous amount of silt into Sharm Obhur, which smothers the benthic animals and kills them (Fig. 5). The observed sedimentation rate was found to be higher at Site 9, which receives stormwater drainage water, followed by Site 8. Moreover, two clusters are formed in the statistical results based on the degree of sedimentation observed at the selected study sites (Fig. 5a). One cluster is formed between Site 9 (stormwater discharge site) and Site 8 (drainage site) with 80% similarity, and the other cluster is formed between the entrance of the creek and the faculty jetty with 90% similarity.

Fig. 5
figure 5

Sedimentation rate on the selected study sites at Sharm Obhur. T sediment trap replicates; ST sites

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Nutrient parameters such as inorganic phosphate (IP), silicate, nitrate and nitrite were analysed, and the results are presented in Fig. 6. The average phosphate concentration in Sharm Obhur is 0.59 μg L−1, whereas the ammonia concentration was 0.8259 μg L−1. Similarly, the mean levels of silicate, nitrate and nitrite in Sharm Obhur were 8.71 μg L−1, 8.73 μg L−1 and 0.53 μg L−1, respectively. The overall mean salinity of Sharm Obhur was 38.45‰.

Fig. 6
figure 6

Nutrient status of Sharm Obhur, Red Sea

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Checklist of scleractinian corals

In the overall biodiversity of scleractinian corals, the acroporid corals were found to have more species (Fig. 7) (21 species). Of the non-acroporid corals (Fig. 8), Faviidae had the most species (17 species), whereas Porites and Goniastrea were the most abundant species. Although Fungiidae has limited species, they were found to be relatively abundant. Overall, approximately 13 families were identified, while 34 genera and 66 species were recorded. The detailed checklist is provided in Table 1.

Fig. 7
figure 7

Acroporid corals of Sharm Obhur, Red Sea. a Acropora selago Studer, 1878; b Acropora secale Studer, 1878; c Acropora hemprichii Ehrenberg, 1834; d Acropora variolosa Klunzinger, 1879; e Acropora abrotanoides Lamarck, 1816; f Acropora samoensis Brook, 1891; g Acropora valida Dana, 1846; h Acropora hyacinthus Dana, 1846; i Acropora humilis Dana, 1846; j Acropora microclados Ehrenberg, 1834; k Acropora valenciennesi Milne Edwards, 1860; l Acropora gemmifera Brook, 1892; m Acropora humilis Dana, 1846; n Acropora monticulosa Brüggemann, 1879; o Montipora stellata Bernard, 1897; p Montipora meandrina Ehrenberg, 1834; q Montipora stilosa Ehrenberg, 1834; r Montipora cocosensis Vaughan, 1918; s Astreopora cucullata Lamberts, 1980; t Astreopora listeri Bernard, 1896; u Astreopora gracilis Bernard, 1896

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Fig. 8
figure 8

Non-Acroporid corals of Sharm Obhur, Red Sea. a Plerogyra sinuosa Dana, 1846; b Favia speciosa Dana, 1846; c Platygyra daedalea Ellis & Solander, 1786; d Platygyra lamellina Ehrenberg, 1834; e Diploastrea heliopora Lamarck, 1816; f Lobophyllia corymbosa Forskål, 1775; g Favia lacuna Veron, Turak & DeVantier, 2000; h Favia stelligera Dana, 1846; i Favites complanata Ehrenberg, 1834; j Mycedium elephantotus Pallas, 1766; k Goniastrea peresi Faure & Pichon, 1978; l Pocillopora damicornis Linnaeus, 1758; m Stylophora subseriata Ehrenberg, 1834; n Pachyseris speciosa Dana, 1846; o Acanthastrea hillae Wells, 1955; p Echinopora forskaliana Milne Edwards & Haime, 1849; q Oulophyllia crispa Lamarck, 1816; r Galaxea fascicularis Linnaeus, 1767; s Gardineroseris planulata Dana, 1846; t Hydnophora microconos Lamarck, 1816; u Fungia scruposa Klunzinger, 1879

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Table 1 Checklist of scleractinian corals recorded at Sharm Obhur
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Discussion

Coral cover of the Jeddah vicinity increases from nearshore to offshore environments (Roik et al. 2016a). Collectively, the results obtained in association with the multivariate analyses suggest that sedimentation may affect the available coral reef resources in Sharm Obhur. Several studies analysing seawater quality and bottom sediment have been conducted in recent years and indicate the devastating effects that have been observed in this creek. Previous studies on the dissolved oxygen concentrations have revealed that the Central Red Sea waters are oligotrophic (El-Rayis and Eid 1997; Roik et al. 2016b). However, recent coastal urbanisation has increased the drainage and rainwater, both of which have changed the environment into a eutrophic area, which has resulted in the abundance of algal assemblages at polluted sites. Studies on the near-shore reefs closer to the sources of discharge sites of Jeddah revealed that chlorophyll a and other nutrient concentrations were 10-fold higher than the offshore sites. Total nitrogen values were also higher in the domestic waste water inlet areas like Site 9 (Sawall and Al-Sofyani 2015). The occurrence of heavy metals such as Zn, Mn and Cu indicates that the creek is in its early stage of pollution (Saad and Fahmy 1984). Basaham et al. (2006) stated that the Fe, Al, Mn, Cu, Zn, Cr and V concentrations in the bottom sediments of Sharm Obhur have greatly increased over the past 18 years due to an influx of domestic sewage.

Many of the coastal resorts and floating restaurants located in Sharm Obhur directly discharge their untreated wastewaters into the creek, which results in an abundance of soft coral. Hence, the soft coral population was predominantly observed throughout the Sharm Obhur reefs. The mean cover of soft corals (44.50%) was found to be higher than that of other types, especially at Site 9, followed by Site 6 (44%). In addition, soft corals were also significantly observed at Site 4 (33.40%). Sedimentation also leads to increased turbidity and enhanced deposition at discharge points. Sedimentation and eutrophication are the major causes of coral reef degradation worldwide (Ginsburg 1993; Marimuthu et al. 2010, 2013; Wilson 2009; Wilson et al. 2005; Rogers 1990; Wolanski and De’ath 2005; Loya 1976) and can also affect the settlement of coral larvae (Goh and Lee 2008). This influx affects not only the sedentary benthic organisms but also the hydrologic systems by increasing the impervious surfaces and leads to coastal pollution (Booth and Jackson 1997). Moreover, stormwater runoff from the various parts of the city carries hydrocarbons, heavy metals and other toxicants that are harmful to sensitive coral reefs (Fabricius 2005).

Conclusion

Although many disturbances are present in Sharm Obhur, the coral reefs are found to have high diversity in the unpolluted areas. Hence, to protect the coral reefs of this region, this study recommends a long-term continuous monitoring programme in Sharm Obhur. In addition, this study also recommends an upgrade and expansion of the existing stormwater systems. The runoff should be directed to a non-reef environment such as Wadi Al Kura, which is a freshwater channel at the end of the creek that can be utilised to mitigate the sedimentation impacts on the reef ecosystem.