New mangrove ecosystem data along the UAE coast using remote sensing A. Al Habshi,1 T. Youssef, 2,∗ M. Aizpuru, and F. Blasco3 1Abu Dhabi Company for Onshore Oil Operations (ADCO), PO Box 270, Abu Dhabi, UAE 2Biological Department, UAE University, PO Box 17551, Al Ain, UAE 3Laboratoire d’Ecologie Terrestre, CNRS/Universit´eToulouse III, France ∗Corresponding author: [email protected] Characteristics of mangrove communities along the Gulf Coast of the UAE were explored using high- resolution satellite data Terra ASTER imageries in the common visible and near infra-red bands. Mangrove stands in three geographically distinctive sites, Khor Kalba, Khor Umm Al-Quwain and Al Dabbiya, were studied through spatial data and ground verification surveys. Mangroves in the UAE appear in patchy and scattered patterns, occupying about 40 km2 of the coastal zone, half of which are located in Abu Dhabi in sheltered lagoons. The remaining areas are linear communities fringing tidal waterways distributed along intertidal zones. Their distribution is limited however, by aridity and site topography. Despite similarities in substrate conditions, differences in climatic and vegetation characteristics be- tween the three sites indicate that growth conditions seem to be more favourable at Khor Kalba with the higher winter temperatures and higher annual rainfalls. Nine main units were recognized on the colour composite image of the Terra ASTER space data; dense vegetation, scattered vegetation, algal deposits, dry sand, sabkhas, settlements, recent deposits and turbid water, shallow water and deep water. Radiance did not allow for the separation of mangrove areas from inland vegetation through the supervised classification. Confusion was also encountered between different soil classes (e.g. wet soils) and settlements or roads. It is concluded, therefore, that satellite data such as SPOT and Terra ASTER can be effectively analyzed through visual interpretations supported by local digital enhancement. Keywords: mangrove, ground verification, Arabian Gulf Introduction Theophrastus over 2,000 years ago (Spalding et al., 1997). Mangroves comprise a biologically significant The Arabian Gulf represents one of the northern and productive component of the land-sea interface limits to mangrove distribution in the region. It is of tropical and subtropical regions of the world. Only one of the most arid of all mangrove ecosystems, 125–130 km2 of mangroves are recognized in the with the least vegetation biodiversity in the world. Gulf, 80% of which are on the Iranian side. Despite Only one species, Avicenna marina, has managed their limited size, mangroves in the Gulf were the to survive and dominate the mangrove ecosystem first to be recorded in the literature by Nearchus and along the Gulf coast of Bahrain, in Qatar with a 309 Aquatic Ecosystem Health & Management, 10(3):309–319, 2007. Copyright C 2007 AEHMS. ISSN: 1463-4988 print / 1539-4077 online DOI: 10.1080/14634980701512525 Downloaded from http://read.dukeupress.edu/aehm/article-pdf/10/3/309/891632/309habshi.pdf by guest on 30 September 2021 310 Al Habshi et al. / Aquatic Ecosystem Health and Management 10 (2007) 309–319 decrease in population towards the north western (February–March 2002) and summer (July–August part of the inner Gulf. Mangrove trees are not found 2002 and in February 2005). Inter-annual variation in Kuwait and most of the north eastern coasts of of climatic factors between 2001 and 2003, includ- Saudi Arabia (ROPME, 1999). However, there is ing annual rainfall and temperature variations were evidence that Rhiozphora mucronata has previously also recorded for the three localities. occurred in the Gulf (B¨oer and Lieth, 1999). The structure of mangrove stands was mea- Mangrove ecosystems inaccessibility is the main sured as described by Cintron and Schaeffer-Novelli obstacle for traditional ecological surveys (Spalding (1984). Five transects were randomly selected and in et al., 1997). Subsequently, the number of studies re- each transect six sampling points were carefully lo- lated to mangrove ecology using satellite data is now cated and four quarters were established by crossing increasing. As the approaches involved are not fully the compass direction of the transect line with the developed, only a few of these studies were related to perpendicular line. Subsequently, a total of twenty- arid mangrove ecosystems. The quality of the satel- four points were sampled on each transect. The dis- lite products is generally dependant on the climatic tance between trees, the diameter of each tree at conditions and the nature of the vegetation to be breast height (dbh), its height and mean basal area examined (Blasco et al., 2001). Even with the aid were recorded. of satellite data, vegetation analysis remains com- At each point in the various transects, a surface plex, time consuming and in most cases ground ver- soil sample (0–15 cm) was collected and analyzed ification is necessary to discriminate against other for the determination of soil moisture. Air-dried coastal vegetation (ERWDA/JODCO/ARSA, 2003). soil samples were analyzed using Micro-Kjeldahl This study explores the characteristics of man- for plant available Nitrogen. Potassium, Phosphorus grove communities in the hyper arid environment of and Calcium were estimated using atomic absorp- the Gulf Coast of UAE using high-resolution satel- tion (Aventa, USA). Salinity was measured using a lite Terra ASTER imageries in the common vis- hand held refractometer, (ATAGO, Japan). ible and near infra-red bands. The specific aim of this work is to distinguish between structural char- Remote sensing studies acteristics of mangrove stands in three geographi- Due to their vast discontinuous distribution cally distinctive sites along the hyper arid coast of around the world, often in the form of narrow belts, UAE; Khor Kalba, Khor Umm Al-Quwain and Al it is almost impossible to monitor mangrove ecosys- Dabbiya. tems without having easy access to satellite technol- ogy (Spalding et al., 1997). Even with these facil- Materials and methods ities, the task remains extremely complex and time consuming. Study sites The type of satellite products that are at our dis- posal primarily determines the applications of satel- Three tide-dominated vegetation type-sites were lite technology to coastal vegetation studies. They selected for this study; Khor Umm Al-Quwain (Lat. also depend on the climatic conditions and on the 25◦32N, Long. 55◦35E), including 8.5 km2 of man- correlated nature of the vegetation. groves; Al Dabbiya (Lat. 24◦15N, Long. 54◦10E) Although the number of references related to with about 3.6 km2 of mangroves; and Khor Kalba mangrove studies using satellite data are progres- (Lat. 25◦05N, Long. 56◦25E). These test sites se- sively increasing since the launch of the first high lected from the west to the east coastline offer the resolution instrument (SPOT 1 in 1986), our general advantage of illustrating a gradient of “Continental- bibliography showed that only about 10, at the most, ity” from the inner to the outer Gulf (Figure 1). are devoted to mangroves of arid coasts. This means Ecological surveys were performed over these that these approaches are still at a research level. This three different localities to identify aridity gradi- study focused on the coastlines of the United Arab ents that could explain the biological and environ- Emirates, on the three test sites described above. mental differences between the concerned sites and The purpose of this experiment is to test the possible distinct vulnerabilities of mangrove species ability of high-resolution satellite data (in the com- and habitats. Three ecological field surveys of man- mon visible and near infra-red bands) for map- grove vegetation, water and sediments were carried ping mangrove communities in arid environments. out over the localities described above in winter This study also aims at understanding the structural Downloaded from http://read.dukeupress.edu/aehm/article-pdf/10/3/309/891632/309habshi.pdf by guest on 30 September 2021 Al Habshi et al. / Aquatic Ecosystem Health and Management 10 (2007) 309–319 311 Figure 1. The three study areas along the UAE coast. characteristics of mangrove stands in Khor Kalba, AST L1B:003 2008703534, 30 September 2002 on Khor Umm Al-Quwain and Al Dabbiya in the UAE. Umm Al Quwain We discuss to what extent the differences found AST L1B:003. 2008765442, 5 July 2002 on Kalba. in these three test sites determine habitat specific conditions and the input of satellite data for the These images were processed following the method study and monitoring of these arid coastal ecosys- illustrated by ENVI and IDRISI software. Out of the tems. Based on the recent development regarding 14 ASTER channels (2 visible, 1 near infra-red, 6 the use of remote sensing for coastal vegetation middle infra-red, 5 thermal infra-red), only 3 chan- studies in the United Arab Emirates, using Terra nels were registered through ENVI software: ASTER sensors (ERWDA/JODCO/ARSA, 2003), we used high-resolution satellite coverage, or Terra Band 1 (0.52–0.60 μm), green ASTER imageries. Three recent ASTER scenes Band 2 (0.63–0.69 μm), red (15m ground resolution in visible and near infra- Band 3N (0.78–0.86 μm), near infrared. red bands) were acquired through Eros Data Center (US Geological Survey) facilities: These 3 visible and near infra-red bands only have a ground resolution of 15m, instead of 30 m for middle or short-wave (SWIR) infra-red and AST L1B:003:2007218008, 10 June 2002 on Al 90 m for thermal infra-red. The processing level Dabbiya was 1B, meaning data has been radiometrically and Downloaded from http://read.dukeupress.edu/aehm/article-pdf/10/3/309/891632/309habshi.pdf by guest on 30 September 2021 312 Al Habshi et al. / Aquatic Ecosystem Health and Management 10 (2007) 309–319 geometrically corrected and is re-projected on UTM is higher (around 40 km2).