Current status of coral reefs in the United Arab Emirates: Distribution ...

Marine Pollution Bulletin 105 (2016) 515–523

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Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul

Current status of coral reefs in the United Arab Emirates: Distribution, extent, and community structure with implications for management Raymond E. Grizzle a, Krystin M. Ward a, Rashid M.S. AlShihi b, John A. Burt c,⁎ a b c

Department of Biological Sciences, School of Marine Science and Ocean Engineering, University of New Hampshire, Durham, NH 03824, USA Ministry of Environment & Water, Marine Environment Research Department, Umm Al Quwain, United Arab Emirates Center for Genomics and Systems Biology, New York University Abu Dhabi, P.O. Box 129188, Abu Dhabi, United Arab Emirates

a r t i c l e

i n f o

Article history: Received 22 June 2015 Received in revised form 1 October 2015 Accepted 5 October 2015 Available online 21 October 2015 Keywords: Arabian Gulf Sea of Oman Gulf of Oman Habitat mapping Degradation Coral bleaching

a b s t r a c t Coral reefs of the United Arab Emirates were once extensive, but have declined dramatically in recent decades. Marine management and policy have been hampered by outdated and inaccurate habitat maps and habitat quality information. We combined existing recent datasets with our newly mapped coral habitats to provide a current assessment of nation-wide extent, and performed quantitative surveys of communities at 23 sites to assess coral cover and composition. Over 132 km2 of coral habitat was mapped, averaging 28.6 ± 3.8% live coral cover at surveyed sites. In the Arabian Gulf low cover, low richness Porites dominated communities characterized western Abu Dhabi, while reefs northeast of Abu Dhabi city generally contained higher richness and cover, and were dominated by merulinids (formerly faviids). Distinct communities occur in the Sea of Oman, where cover and richness were low. We provide management recommendations to enhance conservation of vulnerable coral reefs in the UAE. © 2015 Elsevier Ltd. All rights reserved.

1. Introduction Historically, coral reefs of the United Arab Emirates (UAE) were among the most extensive in northeastern Arabia. Records from the 1960s and 1970s describe extensive Acropora dominated reefs extending across most of the Arabian Gulf coast, occupying hundreds of hectares of near-shore waters from western Abu Dhabi to Ras Al Khaimah (Kassim, 1969; Kinsman, 1964; Purser and Evans, 1973; Shinn, 1976). Coral reefs were also widely distributed across the northern emirates and along the UAE's east in the Sea of Oman (Purser and Evans, 1973). Over the past several decades there has been rapid degradation of coral reefs across the UAE as a result of increasing natural and anthropogenic stressors (Sale et al., 2011; Sheppard et al., 2010). Channelization, reclamation, and port development associated with the oil boom impacted reefs in parts of Abu Dhabi in the 1970s and 1980s (Burt, 2014; Evans et al., 1973; Murray, 1970; Neuman, 1979), but reefs in most of the country remained relatively intact through this period (George and John, 2000b; John and George, 1999; Purser and Evans, 1973). This changed in the late-1990s when two major thermal bleaching events (1996 and 1998) impacted reefs throughout the southern Arabian Gulf and resulted in the loss of N90% of coral in many areas (Riegl, 2002; Sheppard and Loughland, 2002). Formerly ⁎ Corresponding author. E-mail address: [email protected] (J.A. Burt).

http://dx.doi.org/10.1016/j.marpolbul.2015.10.005 0025-326X/© 2015 Elsevier Ltd. All rights reserved.

dominant Acropora were decimated throughout the entire country during these events, surviving only around offshore islands and in isolated pockets in Dubai and Sharjah, and reefs shifted to a lower cover, lower complexity community largely made up of bleachingresistant poritids and merulinids (formerly known as faviids) (George and John, 2000a; Riegl, 2002; Sheppard and Loughland, 2002). Although there have been isolated signs of recovery in some areas (Burt et al., 2008), recurrent bleaching events in subsequent years and increasing pressure from coastal development have maintained reefs throughout much of the southern Arabian Gulf in a relatively degraded state (Burt, 2014; Burt et al., 2011a, 2016; Riegl and Purkis, 2012a). Coral communities on the UAE's Sea of Oman coast have similarly undergone decline in recent years. Although reefs there had largely recovered from impacts of the 1990s bleaching events, the occurrence on Cyclone Gonu (2007) and a large-scale harmful algal bloom (2008/9) resulted in widespread degradation of the UAE's eastern reefs in recent years as well (Bauman et al., 2010; Burt et al., 2016–in this issue; Foster et al., 2011). Despite the widespread nature of events affecting UAE reefs and the magnitude of their impacts, the absence of a nation-wide monitoring network has prevented an assessment of the status of today's reefs in either extent or condition (Burt et al., 2014; van Lavieren et al., 2011). Much of our knowledge of the distribution of coral reefs in the UAE is based on maps that are now outdated and inaccurate. National-level maps of the distribution of coral reefs in the UAE were largely produced from anecdotal reports rather than detailed field surveys (e.g. UNEP maps; Spalding et al., 2001), with much of the purported ‘reef’ habitat

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2. Methods

it appeared in the imagery; 2) identification of bottom features likely representing live coral habitat; 3) ground-truthing of selected sites with towed underwater videography and/or snorkeling; and 4) production of final maps showing location, shape, size and relative densities of live coral habitats. All imagery analysis and final map production was done using ArcGIS 10 software. Towed underwater videographic imagery following the general methods described in Grizzle et al. (2008) was obtained to groundtruth the satellite imagery, as well as to inspect bottom areas that potentially had coral habitat. The video system consisted of a SeaViewer model 550 color video camera/DVR recorder system with the camera mounted on a custom-made sled deployable in bottom or suspended modes, with a WAAS enabled GPS unit used for georeferencing (Garmin 18x, 76CSx, or 541 s; advertised 3-m accuracy). The standard protocol was to collect video imagery (30 frames/s) with horizontal position recorded near-continuously along each shiptrack. Typically, one transect of 20–50 m length was navigated at a ship speed of 2–4 km/s in order to ground-truth a site. The video imagery was viewed in real-time and recorded in digital format (AVI files) continuously in all areas surveyed. In select areas, particularly where coral habitat was not visible in the GeoEye imagery, the spatial extent of coral habitat was delineated by navigating multiple parallel transects. All imagery was reviewed in the laboratory and visually classified into one of three categories: “non-reef” (no live coral cover), “low density” reef (≤ 50% live coral cover), and “high density” reef (N50% cover by live coral).

2.1. Study area

2.3. Quantitative reef surveys

The present study included surveys on both the Arabian Gulf and Sea of Oman coasts of the UAE, including coral habitats in all seven emirates (Fig. 1a).

Detailed quantitative surveys of reef benthos and the coral community were performed at 23 sites along both the Arabian Gulf and the Sea of Oman coasts of the UAE (Fig. 1). These sites represented most known major reef areas in the emirates as well as a number of previously undocumented reef sites that were identified during this study, providing a detailed large-scale dataset on the current status of coral reefs throughout the nation. Sites included both natural reefs as well as several large-scale breakwaters upon which extensive coral communities have developed and which serve as the dominant coral habitat in large parts of the UAE where the seabottom is mainly sand (Burt et al., 2011a, 2012). In all, quantitative reef surveys were performed at 10 sites in Abu Dhabi, 4 sites in Dubai, 2 sites in Sharjah, 4 sites in Umm Al Quwain, 1 site in Ras Al Khaimah, and 2 sites located within marine protected areas in Fujairah. Breakwater reefs included the Dubai waterfront and Palms in Dubai, the Sharjah Port, and the Saqr Port in Ras Al Khaimah. All sites in these areas were surveyed between April and December 2012. At each site, replicate 0.25 m2 quadrats were photographed at 3 m intervals along each 30 m transect with a Nikon D90 underwater digital camera mounted on a PVC frame outlining the quadrat area, for a total of 11 photoquadrats per transect and 66 photoquadrats at each site. In total over 1500 high resolution images of reef bottom were collected for analyses for this study. Each digital photoquadrat image was optimized using Adobe Photoshop and analyzed with CPCe image analysis software. A total of 50 random points were assigned to each photograph, and benthos underlying each point was classified to the lowest taxonomic level possible. This technique has been successfully applied in several earlier studies of coral reef communities in the area (Burt et al., 2008, 2011a, 2013). Images were analyzed to estimate the percent cover of dominant benthic categories at each reef (live coral, dead coral with turf algae, fleshy algae, coralline algae, urchins, other live, and sand/pavement). The total number of coral species observed in transects was tabulated for each site and estimates of percent live coral cover and the relative composition of coral families contributing to the community were generated. Spatial differences in coral cover between sites was assessed using ANOVA on transect data; cover data were arcsine squareroot

mapped prior to the onset of major stress events in the 1990s and later. While some components of these maps have been updated using ground-truthed remote sensing (e.g. in Abu Dhabi waters in the mid-2000s; EWS-WWF, 2008), this data is now slightly outdated due to more recent stressors (e.g. the 2010 bleaching event) and have not been updated for the majority of the UAE's coastal waters. In addition to our limited understanding on the extent of reefs, the condition of even accurately mapped reefs remains largely unknown (Burt et al., 2011a). While several studies have described coral communities at specific sites in the UAE (e.g., Burt et al., 2008; Foster et al., 2011), there is limited information on the condition and composition of coral communities on a national scale. To address these knowledge gaps and to provide information for improved conservation and management, the purpose of this study was to map and assess coral resources across the UAE. Mapping efforts were primarily targeted towards reefs outside of the recently mapped Abu Dhabi emirate (EWS-WWF, 2008), and quantitative surveys of coral communities were performed in all seven emirates to provide a contemporaneous assessment of reef condition and community structure across the nation. Such information is critical to guiding marine management and conservation efforts, and will serve as a benchmark against which future changes in reef condition and extent can be assessed.

2.2. Map production Comprehensive mapping of UAE corals is difficult because typically used remote sensing methods (e.g., satellite imagery) are not capable of detecting corals at water depths exceeding 5 to 10 m (particularly in the Arabian Gulf) due to water clarity limitations (Purkis and Riegl, 2005; Purkis, 2005). Corals occur in some areas at depths N15 to 20 m in the Arabian Gulf (Basson et al., 1977; EWS-WWF, 2008; Harris and Schroder, 2006), but the UAE-wide spatial extent of these deeper corals is not known. Therefore, we used a combination of previously published maps, new high-resolution satellite imagery and underwater videography to produce a comprehensive geodatabase of coral reef habitat on both coasts (Arabian Gulf and Sea of Oman) of the UAE. The coral reef maps herein were produced from four sources: (1) downloadable United Nations Environment Programme, World Conservation Monitoring Centre's “Global Distribution of Coral Reefs, 2010” ArcGIS file (UNEP-WCMC, 2010); (2) printed maps published in a widely used SCUBA divers manual by Harris and Schroder (2006); (3) newly acquired GeoEye-1 high resolution satellite imagery; and (4) towed underwater videography recorded in 2012 and 2013 as part of this study. The map information differs widely among the four in content as well as spatial and thematic accuracy due mainly to the original data sources and methods used. However, we chose to use all four because together they contain information that represents the most comprehensive description of the spatial distribution of live coral reef habitat in the UAE currently available. The GeoEye-1 imagery used was recorded between 2010–2012, with the following data specifications: pan-sharpened, b1.0 m resolution, 4-band (blue, green, red, near-infrared), orthorectified to positional accuracy of 10 m, in GeoTIFF format with 11-bit radiometry. The imagery was purchased from MapMart (10465 Park Meadow Drive, Lone Tree, CO 80124 USA). The general protocol consisted of four steps (see Grizzle et al., 2013 for details): 1) determination of “signatures” (based on visual inspection of the imagery) for coral habitat as


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Fig. 1. (A) Overview maps showing mapped coral reefs in the UAE based on UNEP-WCMC (2010) dataset (black polygons) and the present study (white dots), locations of 24 sites where coral and other benthos were quantitatively sampled for the present study (white triangles), and locations of 12 live coral reefs described in Harris and Schroder (2006) (gray squares). (B) and (C) close-ups of coral distribution in northern emirates and east coast, respectively; note black polygons based on UNEP-WCMC (2010) data showing approximate shape/size of reefs, and white dots based on present study showing only the location (most reefs too small to show at map scale). See Table 1 for summary data on areal coverages by emirate. See Supplementary Table 1 for coordinates of all reefs shown except in Abu Dhabi.

transformed prior to analysis to improve normality. Overall coral community structure was also examined with multivariate approaches using Primer 6.0. Prior to multivariate analyses, data were pooled for each site and proportional coral cover data were arcsine-square root transformed to normalize the data. To avoid the influence of outliers on multivariate analyses, species occurring in b3% of samples were

removed prior to analyses as recommended by Tabachnick and Fidell (2001) and McCune and Grace (2002). A hierarchical agglomerative cluster analyses was performed on a Bray–Curtis similarity matrix to generate a dendrogram illustrating coral community groups, and a SIMPROF analysis was used to test for significant differences in coral community structure between groups. Species characterizing each

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distinct cluster of coral communities were subsequently identified using SIMPER analyses on transect data represented by each group, with each species contributing N 10% of the community similarity included. 3. Results 3.1. Coral distribution patterns Coral reef habitat occurs in coastal areas throughout the UAE, with coral habitat found in all seven emirates and on both coasts. Fig. 1a combines mapping data from the present study and the online UNEP-WCMC (2010) dataset, which for the UAE is based on the EWS-WWF (2008) project for Abu Dhabi and the much earlier UNEP/IUCN (1988) data for the other emirates. Table 1 summarizes coral habitat area by emirate, and Fig. 1b and c show details for coral in areas outside of Abu Dhabi (see Supplementary Table 1 for coordinates and other information on all reefs mapped in the present study). The total area of mapped coral habitat is N 13,000 ha (N 130 km2). More than 90% of UAE's mapped reefs are in the Arabian Gulf, with the remainder in the Sea of Oman (Table 1). The overall coral distribution pattern in the Arabian Gulf indicates a greater concentration of coral habitat in central and western Abu Dhabi compared to other areas (Fig. 1). This largely reflects a preponderance of shallow (b10 m) habitats in Abu Dhabi suitable for classification by satellite imagery (e.g. EWS-WWF, 2008), as well as greater availability of hard-bottom habitats suitable for corals relative to the other emirates. In addition to mapping corals in natural habitat, this study also documented the spatial distribution of corals on some major manmade breakwaters (Fig. 1b), many of which occurred in areas where natural hard-bottom habitat was uncommon. The high-resolution (b 1 m) satellite GeoEye-1 imagery used here detected bottom features in water depths b 10 m, as well as in deeper areas with less turbid water (e.g. Sea of Oman). The overall result was N40 newly mapped coral reefs, with particular concentrations on the east coast and in the extensive lagoon system in Umm Al Quwain (Fig. 1b–c; see also Supplementary Table 1). In contrast to the near lack of natural rock outcrops in the Arabian Gulf, Sea of Oman reefs were mainly associated with rocky outcrops extending from coastal mountains and hills into the subtidal waters. Much of the coral in Fujairah is concentrated in the northern portion of the emirate where there are abundant outcrops and naturally submerged rock. In contrast, the southern portion of Fujairah is mainly dominated by soft-sediment sandy beaches with the mountainous areas several kilometers to the west. 3.2. Quantitative coral reef surveys Detailed quantitative sampling of 23 coral reef sites across the UAE showed geographic differences in benthic composition and coral community structure across the nation (Fig. 2). In general, reef benthos in the UAE was dominated by a mixture of live coral and algae-covered dead coral skeleton, which comprised 28.6 ± 2.1% and 37.3 ± 2.9% of the substrate, respectively, on average (Fig. 2a). Live coral cover varied significantly among sites (ANOVA F(22,115) = 49.8, p b 0.001) Benthic

composition, coral species richness, and coral community composition showed spatial patterns that were generally consistent with environmental conditions (see Bauman et al., 2012 for environmental characteristics). Coral communities in the environmentally extreme western Abu Dhabi (Mukasab to Al-Hiel), were generally low in live coral and contained relatively high amounts of dead coral (Fig. 2a); the exception was Hawksbill reef which was made up almost entirely of the stresstolerant coral Porites harrisoni (N90% of coral). These sites generally also had the lowest species richness of all locations in the UAE (Fig. 2b), with communities that were heavily dominated by Porites (mean: 87% of coral; Fig. 2c); species richness at Delma was over a third higher than at other western region sites, reflecting the reduced environmental stress at this offshore island with deeper surrounding water. Coral communities in eastern Abu Dhabi and Dubai (Dhabiya to Palm Jumeirah) contained among the highest coral cover of all sites examined in the UAE (mean: 42.0% cover) and nearly twice the species richness of sites in western Abu Dhabi (mean: 23.3 vs 12.8, respectively); these were also among the most extensive reefs observed during mapping surveys (see above, Fig. 1). There was a distinct transition in community structure in eastern Abu Dhabi and Dubai, with merulinids (formerly faviids) dominating these reefs (50.9% of coral), while the relative abundance of portitids here was half of that observed on the western reefs (43.7 vs. 87.1% of coral, respectively; Fig. 2c). The transition in community structure continued with distance from the extreme southwestern Gulf, coral communities from Sharjah to Ras Al Khaimah showed a continued decline in the relative abundance of poritids, while acroporids, dendrophyllids, and siderastreids became relatively more common compared with sites in the southwest (Fig. 2c). It should be noted that despite a number of these sites being in relatively hostile environments (turbid near-shore habitats and lagoonal systems) resulting in relatively low coral cover observed (mean: 20.9%; Fig. 2a), the Gulf's northeastern reef sites contained the highest average species richness (mean: 23.7 species per site) and included a breakwater coral community with the highest richness observed in this study (Fig. 2b). At the remaining sites in the Sea of Oman, live coral cover was low and bare pavement high (mean: 14.3% and 59.7%, respectively; Fig. 2a), reflecting the widespread coral loss that had occurred in this area following a large-scale algal bloom in 2008/9. Species richness at these sites was modest compared to sites elsewhere in the UAE, with the community at Dibba being dominated by the pocilloporid, Pocillopora damincornis, while Al-Aqah was mainly dominated by the poritid, Porites lobata, and the merulinids, Platygyra daedalea and Platygyra sinensis (Fig. 2b,c). Multivariate analyses showed that corals in the United Arab Emirates fell into five distinct community clusters that differed significantly from one another (Fig. 3; SIMPROF test: p b 0.001 for each pairwise contrast). The coral communities at the two reefs located on the UAE's Sea of Oman coast (Dibba and Al-Aqah) were distinct from each other, and from all sites in the Arabian Gulf. In Dibba, P. damincornis was strongly associated with this community (contributing 95% to the group similarity), reflecting its relatively common abundance in Dibba (7.1% of benthic cover) versus its complete absence from all other locations in the UAE, and the high similarity (65%) within this group (Table 2). Similarly, the coral community at Al-Aqah had relatively

Table 1 Summary of UAE coral reef habitat area by emirate based on a combination of UNEP-WCMC (2010) data and the present study. AG = Arabian Gulf, GO = Sea of Oman. Emirate

Coral area (ha)

Water body (AG or GO)

Notes

Abu Dhabi Dubai Sharjah Ajman Umm Al Quwain Ras Al Khaimah Fujairah

7951 324 735 324 1577 2306 15

AG AG AG and GO AG AG AG GO

UNEP-WCMC (2010) data only. Includes substantial colonization of breakwaters. Includes offshore islands in AG; does not include reefs roughly mapped in Harris and Schroder in GO (2006). Based on estimated portions of reefs that extend into Sharjah waters. Includes substantial number of lagoon reefs. Present study indicated a likely loss of major “deepwater” reefs. Does not include reefs roughly mapped in Harris and Schroder (2006).

Total: 13,232 ha.


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Fig. 2. Details of the benthic and coral community at each site that was quantitatively surveyed. a) Percent cover of each of the major benthic components, b) total species richness of corals observed within transects at each site, and c) relative abundance of coral families observed in transects at each site (as % of coral cover).

high abundance of P. lobata (10.5% of substrate) relative to all other sites (mean b 1%), leading to this site being a distinct coral community group of its own. Within the Arabian Gulf, three distinct coral communities were observed: one representing a distinct coral community in the lagoonal system in Umm Al Quwain (UAQ-Reef3), one representing all sites in western Abu Dhabi (from Mukasab to Al-Hiel), and one comprising all remaining sites in the Arabian Gulf, from eastern Abu Dhabi, through Dubai, to Ras Al Khaimah. The community in the Umm Al Quwain lagoon site 3 was characterized by very low coral cover (1.9% of substrate), but was composed of a unique mix of Acropora, various merulinids, Porites, and siderastreids (see Fig. 2 above) which contributed to its being a distinct group. The remaining groups – the western Abu Dhabi group and the eastern Abu Dhabi to Ras Al Khaimah group – were segregated mainly by differences in the relative abundance of poritids versus merulinids. Western Abu Dhabi sites were heavily dominated by stress-tolerant P. harrisoni, which made up over a fifth of the benthos at sites within this group and contributed to nearly all of the similarity (85%) in this coral community (Table 2). In contrast, the eastern Abu Dhabi to Ras Al Khaimah coral community was mainly characterized

by merulinid species (see Table 2), which together contributed nearly two-thirds of the cumulative similarity in this group, with Porites lutea contributing and additional 12% to similarity. 4. Discussion Coral reefs in the United Arab Emirates have undergone considerable change in the past several decades. The results of this study provide much needed information on the current distribution, extent, and structure of coral communities around the UAE, allowing for improved management of these important ecological assets. Thus, the following discussion focuses on management implications with a concluding synthesis section. 4.1. Coral distribution patterns Although coral reefs of the UAE have been considerably impacted by both natural and anthropogenic disturbances in recent decades, our results show that there are substantial coral reef resources present

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Fig. 3. Dendrogram of coral community structure at reef sites around the United Arab Emirates from cluster analysis. Bold horizontal lines next to the site names delineate the five distinct communities identified by SIMPROF analysis (p b 0.05); gray sub-branches do not differ significantly (p N 0.05).

throughout the nation, with over 132 km2 of coral reefs occurring across all seven emirates. Perhaps the most striking feature of the overall coral distribution pattern in the Arabian Gulf is the apparent concentration of coral habitat in central and western Abu Dhabi compared to other areas (Fig. 1A). This is largely due to the preponderance of waters b 5 m in depth in these areas, and the fact that satellite imagery was used as the primary dataset for most of the coral mapping in these areas (EWS-WWF, 2008). As noted above, satellite imagery is not effective for coral mapping in water N 5 to 10 m deep in the Arabian Gulf. Before the present study, there had been no recent mapping in any of the emirates except Abu Dhabi (EWS-WWF, 2008). Thus, of the previous studies only the mapped reef data for Abu Dhabi in the UNEP-WCMC (2010) dataset are relatively recent and includes documentation of substantial ground-truthing. Secondly, our observations in several areas on both coasts with towed underwater video indicate that live coral reefs occur in waters N5 to 10 m and are perhaps widespread; Basson et al. (1977) indicated that 20 m was potentially the deepwater extent of

coral in the region. Moreover, our observations are mirrored by the fact that most of the well-known dive sites on UAE's east coast (Sea of Oman) are in waters N15 m deep (Harris and Schroder, 2006). Therefore, while it might be concluded that the earlier reef maps may have represented an over-estimate of current reef extent due to the recent losses described above, we still have little knowledge of the extent of coral habitat in waters N10 m deep. In sum, these caveats suggest that our present knowledge of the spatial extent of coral reefs in the UAE is incomplete, and may represent a substantial underestimate if there are extensive “deep water” reefs. Although there is a general knowledge of bottom types and lithification processes in the Gulf, particularly the relatively rapid transformation of sands into “hardground” that provides substrate suitable for colonization by corals, the spatial extent of hard bottoms is not well known (Riegl and Purkis, 2012b). Nonetheless, some general predictions can be made with respect to what may be found when surveys in the deeper waters are conducted. If it is assumed that corals occur

Table 2 Characteristics of the coral communities identified by cluster analysis (see Fig. 3). Mean similarity of transects within each group are indicated, along with the percent cover and percent contribution of the most important coral species within each group. Group

Mean similarity (%)

Dibba

65.1

Al-Aqah

58.7

Species Pocillopora damicornis (Pocilloporidae)

Eastern Arabian Gulf

Western Arabian Gulf

Contribution (%)

7.1

95.1

10.5 2.5

60.6 25.1

Porites harrisoni (Poritidae) Porites lobata (Poritidae)

0.4 0.1

77.3 10.3

Platygyra daedalea (Merulinidae) Cyphastrea microphthalma (Merulinidae) Favia pallida (Merulinidae) Porites lutea (Poritidae)

6.6 4.3 2.2 3.2

29.1 20.1 13.5 12.3

22.1

85.8

Porites lobata (Poritidae) Platygyra daedalea (Merulinidae) UAQ Lagoon Reef 3

Cover (%)

21.0

46.5

59.7 Porites harrisoni (Poritidae)


in water depths up to ~ 20 m in the Arabian Gulf (Basson et al., 1977; EWS-WWF, 2008; Harris and Schroder, 2006), then bathymetric patterns alone indicate the maximum potential distribution of corals. Although not presented here, inspection of available navigation charts (e.g., British Admiralty International Chart Series 2889) indicates extensive areas (100 s of km2) extending up to about 100 km offshore of the mainland in Abu Dhabi and 10 to 20 km offshore in the other emirates on the Arabian Gulf. Thus, the mapped coral reefs shown in Fig. 1 likely represent only a small fraction of actual live coral resources of the UAE. Surveys for coral habitats in these “deep water” areas – as well as other ecologically and economically important habitats such as pearl oyster reefs – using some combination of appropriate mapping methods (e.g., sonar and underwater videography) are much needed, particularly in the Arabian Gulf. The present study also documents the widespread and previously unmapped coral resources along UAE's east coast in the Sea of Oman. The overall result was 21 newly mapped coral reefs, 6 in Sharjah's east coast waters and 15 in Fujairah (Fig. 1c). In contrast to the virtual absence of natural rock outcrops in the Arabian Gulf, Sea of Oman reefs were mainly associated with rocky outcrops extending from coastal mountains and hills into the subtidal waters. This results in a paucity of shallow-water coral reefs off the sand beaches that dominate southern Fujairah, and conversely a concentration of reefs along the northern shoreline of the UAE in the Sea of Oman. Most of these are important dive sites for recreational divers, supporting a substantial ecotourism industry (Harris and Schroder, 2006). In addition to the shallow-water sites mapped with satellite imagery in this study, there are important natural reefs in waters N15 m water depth that are also well-known dive sites. Finally, the present study documents significant amounts of live coral on man-made breakwaters in the Arabian Gulf, often exceeding abundances observed on nearby natural coral reefs (Fig. 1b; see Burt et al., 2009, 2010, 2011b, 2012 for details). Breakwaters associated with coastal development in the UAE are both large and ubiquitous, suggesting that they are likely to play an increasingly important role in coastal ecology (Burt et al., 2011b, 2012; Feary et al., 2011). These breakwaters may serve as effective ‘walls’ for coral larvae drifting along coastal areas following spawning, thereby concentrating settlers on these habitats compared to natural reefs which are more hydrologically open. The biotic communities associated with breakwaters are perhaps more resilient to wind-associated sediment stress as they are typically well elevated above the seafloor where sedimentation stress is highest (Burt et al., 2010), perhaps in part explaining the high cover of coral on these structures. Further research on the importance of these large-scale artificial coral habitats is needed. 4.2. Coral community structure 4.2.1. Shifts in coral community structure Our results indicate that effects of the cumulative stressors that have impacted UAE's reefs in recent decades still persist today, and there are only limited signs of recovery. Western Abu Dhabi, where reefs had once been extensive and Acropora had dominated (Purser and Evans, 1973), is now characterized by low-cover communities heavily dominated by stress-tolerant Porites. While coral cover and species richness was generally higher to the east in the Arabian Gulf, coral cover was predominantly made up by more stress-tolerant merulinids and poritids that had survived earlier bleaching events, while Acropora remained rare at all sites. Patterns of juvenile coral recruitment observed shortly after the bleaching events and in subsequent years suggest that it is unlikely that we will see a return to Acropora dominance in the near to medium term future. Few coral juveniles were observed in western Abu Dhabi in the 3 years following the 1998 bleaching event, and while more abundant in eastern Abu Dhabi the juvenile community was heavily dominated by the formerly subordinate merulinids that had differentially survived bleaching (Sheppard and Loughland, 2002).

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A limited number of Acropora recruits were observed on reefs in eastern Abu Dhabi and Dubai in the early 2000s (Riegl, 2002), and although isolated pockets did show strong recovery in subsequent years (Burt et al., 2008, 2011a), recurrent bleaching events in 2002 and 2010 as well as impacts from coastal development all but negated this recovery (Burt, 2014; Burt et al., 2008; Riegl, 2003; Riegl and Purkis, 2012a). The results of our study indicate that the loss of Acropora is widespread and consistent throughout the coastal Arabian Gulf sites examined here, where it makes up only 1.4% of the coral cover, on average. The near absence of Acropora in coastal reefs is likely to persist into the future. Recent coral settlement studies in Dubai have shown that Acropora remains rare in the recruit community, with most recruits being poritids and other taxa (Bauman et al., 2014). Models suggest that it would take at least a decade of growth and reproduction uninterrupted by further impacts for Acropora recovery to occur (Riegl and Purkis, 2009), which is unlikely given the increasing frequency of impacts from bleaching events and coastal development observed over the past two decades (Burt, 2014; Burt et al., 2014; Riegl and Purkis, 2012a). Today, the only known locations where Acropora has recovered dominance on the UAE's Arabian Gulf coast are around off-shore islands that are distant from urban pressures and which are surrounded by deeper, cooler waters that buffer the reefs from extreme thermal events. An example is Sir Bu Nair, which lies 70 km offshore from Abu Dhabi. This island was heavily impacted by the 1996–8 bleaching events, but recovery began almost immediately and the island has escaped impacts from subsequent bleaching events and coastal development that affected mainland reefs (Riegl, 2003; Riegl and Purkis, 2012a), and now contains dense and extensive Acropora stands as well as a diverse understory of other taxa (Burt et al., 2014; Rezai et al., 2004). A number of other deep-water islands occur at similar distances off-shore from Abu Dhabi that could potentially contain similarly extensive coral communities, but these generally lie within oil concessions or other high security areas that have historically prevented surveys. An assessment of such sites would be extremely valuable, as such off-shore sites likely serve as larval donors to replenish populations impacted on coastal reefs and their secure nature serves to provide them de facto protected area status that may enhance their long-term conservation (Burt et al., 2008, 2011a; Riegl, 2003). Degradation of coral reefs on UAE's east coast in the Sea of Oman has been more recent, but of comparable magnitude. The 2007 supercyclone Gonu was the strongest tropical cyclone on record for the Arabian Sea, where sustained wind speeds were 270 km/h and peak gusts reached 315 km/h (Fritz et al., 2010). The wave energy associated with this storm resulted in considerable loss of corals from reefs throughout the Sea of Oman, with impacts particularly acute on wave exposed reefs dominated by branching corals such as acroporids and pocilloporids (Coles et al., 2015; Foster et al., 2011; Taylor, 2010). On the UAEs east coast, reefs were flattened to near horizontal in several locations and over half of branching coral cover was lost from UAE reefs on average (Foster et al., 2008, 2011). Just a year later, reefs throughout northern Sea of Oman were further impacted by a large-scale anoxia event associated with a harmful algal bloom (HAB). In the UAE there was a near complete extirpation of formerly dominant pocilloporids from reefs and substantial losses of acroporids, with overall coral cover losses N 90% at a number of locations (Bauman et al., 2010; Foster et al., 2011). The observations in this current study reflect the impacts from these recent events, with coral cover generally low on the two major Sea of Oman reefs examined (mean: 14.2%). However, there are also positive signs of recovery, particularly at Dibba, where the pocilloporids and acroporids that had been nearly extirpated during the 2008 HAB event now make up 69% and 9% of live coral cover, respectively. The observation of the onset juvenile recruitment in the year after the HAB event (Foster et al., 2011) and the subsequent return of pocilloporids and acroporids observed in this study suggest that coral reefs on the UAE's Sea of Oman coast have good potential for

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recovery within the next 10–15 years in the absence of further impacts to this area.

4.2.2. Current spatial patterns in community structure Ours is the first study to perform a nation-wide assessment of coral community structure in the UAE. Although there have been several earlier studies of coral community structure that have included data from the UAE, these have occurred either at spatially restricted locations (e.g. Burt et al., 2008; Riegl, 2002) and/or were pooled for comparison with reefs in other regions (e.g. Bauman et al., 2012). Our results suggest that there are broad patterns in community structure in the UAE that relate to differences in the marine environment. Two distinct multi-site communities were identified in the Arabian Gulf which segregated spatially as those in the environmentally extreme western Abu Dhabi (Mukasab to AlHiel) versus all other Arabian Gulf sites (from Dhabiya, near Abu Dhabi City, to Ras Al Khaimah); the remaining communities were site-specific, and included an unusual lagoonal community in Umm Al Quwain and the two reefs surveyed in the Sea of Oman (Dibba and AlAqah). The environmental context of the UAE has long been recognized in driving spatial differences in coral communities. Over a half a century ago Kinsman (1964) commented on the remarkable tolerance of corals to the extreme temperatures and salinity of the southwestern Arabian Gulf. He and his contemporaries showed that the high-cover, Acropora dominated reefs characteristic of much of the southern Gulf at that time gave way to lower cover, lower diversity, Porites dominated reefs in more environmentally extreme areas such as lagoonal systems and the shallow far western embayment of Abu Dhabi (Evans et al., 1973; Kinsman, 1964; Murray, 1970; Purser and Evans, 1973). Although Acropora have been largely extirpated from reefs in the UAE, the same environmentally-related gradient in coral communities is still apparent. Coral communities in the southwestern basin of the Arabian Gulf (Mukasab to AlHiel) are exposed to the most extreme temperatures and salinity in the nation as a result of its shallow depth and constrained circulation, and these communities were also the most heavily impacted by earlier mass bleaching events (Riegl et al., 2012; Sheppard and Loughland, 2002). Our surveys showed that today these communities are low in coral cover and species richness, are heavily dominated by stress-tolerant Porites, and have a unique community structure that is distinct from all other areas of the UAE. Environmental conditions are less extreme for reefs to the east of Abu Dhabi city due to better mixing with deeper offshore waters (Riegl et al., 2012). These environmental differences are reflected in community structure, with all Arabian Gulf sites east of Abu Dhabi city having a comparable community structure that was characterized by higher coral cover, higher species richness, and an increase in the relative abundance of merulinids, siderastreids, and other families with a concomitant decrease in the relative abundance of poritids compared with western sites. Our surveys also showed that the coral communities in the Sea of Oman were distinct from those in the Arabian Gulf. Sea of Oman reefs were characterized by low coral cover as a result of earlier cyclone and HAB impacts and had only moderate diversity, with the suite of species and their relative abundance differing from communities within the Arabian Gulf. For example, some species of coral were observed exclusively at the Sea of Oman sites (e.g. Leptastrea pruinosa) or were markedly more abundant (e.g. P. lobata), while some species that were common in the Arabian Gulf were not observed (e.g. Coscinaria monile) or were less common in the Sea of Oman (e.g. P. harrisoni). These patterns reflect the strong dissimilarity in coral communities that had been described earlier by Bauman et al. (2012), who attributed divergence in coral community structure between the Arabian Gulf and sites elsewhere in the Sea of Oman to differences in temperature, salinity, chlorophyll content, and long-shore current patterns between the two water bodies. Within the Sea of Oman, differences between the two sites were mainly due to one species, P. damicornis, which made

up nearly two-thirds of coral at Dibba, but was not present in transects at Al Aqah (although it was observed outside of transects). The remaining unique community was found only at a single lagoonal site in Umm Al Quwain, which had the lowest coral cover observed at any site in this study (2%), but contained relatively high species richness (16 species compared with the mean of 18.8 species observed across all sites) which is likely a reflection of its proximity to the highly diverse reefs in the Musandam (Salm, 1993). Overall, the results of this and earlier studies indicate that while recent events have had considerable impacts on reefs throughout the UAE, the overall community structure is one that remains strongly influenced by geographic variation in long term environmental conditions. Our results show that despite recent degradation, many reefs in the UAE contain coral communities with substantial live coral cover and considerable species diversity, highlighting the need for robust conservation and management of these important ecosystems. 4.3. Management implications The management implications of our findings center on two topics: marine protected areas and monitoring. Management of the marine resources in general in the UAE includes establishment of marine protected areas (MPAs). Some coral reefs in the UAE are located within established MPAs (Van Lavieren and Klaus, 2013), but many are not, and our study identified a number of important and unique coral reef sites that probably should be. Such sites include the Saadiyat reef in Abu Dhabi, which is one of the most diverse and high coral cover sites in the western UAE that is still relatively unaffected by human activities, as well as the extensive Ras Ghanada reef and reefs in the Umm Al Quwain lagoon system. This lagoon system represents a unique ecosystem which contains diverse and widespread coral communities along with important mangrove and seagrass habitats (Grizzle et al., 2013). The Umm Al Quwain area also had among the highest species abundances of all areas sampled in a recent molluscan shellfish survey (Anderson et al., 2011). Unfortunately, these areas and others are under near-term threat from human activities, and the establishment of MPAs may represent the only mechanism for their conservation. We would also encourage marine managers to consider incorporating large-scale artificial reefs such as breakwaters into MPA networks. While the management focus should be on conserving and restoring natural reefs, the results of this and other studies show that breakwaters represent an incredibly important habitat for coral and fish in the southern Arabian Gulf, often containing abundance and diversity of fauna that exceeds that of nearby natural reefs, particularly in places such as Dubai where availability of hard-bottom habitat is limited. The inclusion of important breakwater reefs into an MPA network would allow for these structures to potentially serve as source reefs for dispersal of coral larvae and adult fish to surrounding natural habitats, potentially enhancing their recovery. Finally, development of a nation-wide monitoring and management program is perhaps the only long-term hope for UAE's coral reefs to recover to their former health, or even to stem the decline that is currently occurring. We suggest that a coral reef monitoring network should incorporate reefs located within established MPAs as well as other areas, and it should focus on the reefs that typically occur on “caprock” substrates but also include corals on breakwaters and other artificial substrates. It is recommended that management agencies expand from almost total reliance on satellite imagery for coral mapping to appropriate underwater methods such as sonar and towed video to map the corals occurring at water depths between 10 and 20 m. These “deep water” corals may be far more spatially extensive then those mapped to date, and are possibly important larval sources for maintaining shallower near-shore populations. While some coral reef monitoring programs have been established in the UAE, the data were collected by different groups, using different techniques, for different purposes and reported to different stakeholders, with no centralized, publicly


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