Distribution of Mangroves along the Red Sea Coast of the ... · Mangrove habitats support marine and avian life in the Red Sea. ... This paper is first part of our study that covers

e-Journal Earth Science India, Vol. 3 (I), January, 2010, pp. 28-42

http://www.earthscienceindia.info/; ISSN: 0974 – 8350

28

Distribution of Mangroves along the Red Sea Coast

of the Arabian Peninsula: Part-I : the Northern

Coast of Western Saudi Arabia

Arun Kumar, M. Asif Khan and Abdul Muqtadir Center for Petroleum and Minerals, Research Institute

King Fahd University of Petroleum and Minerals Dhahran 31261, Saudi Arabia Email:[email protected]

Abstract

Historical Landsat Enhanced Thematic Mapper (ETM) data of the

years 2000 and 2001 were used to numerically illustrate the distribution of mangroves that occur along the northern Saudi Arabian Red Sea coast from Sharm Zubair in the north to Al-Lith in the south. The distribution of mangroves is patchy and they do not occur as a continuous forest and are generally restricted to the low energy quieter environments like bays, narrow channels, and inland faces of offshore islands. However, they also occur in the intertidal environments. At certain locations they occupy very small area that could indicate depletion of mangroves. Due to rapid urbanization and industrialization of this region, traditional land use is changing and adversely impacting sustenance and growth of mangroves. There should be an inclusive policy that promotes economic development and protects mangroves also; this can be achieved as shown by Khan and Kumar (2009) on certain locations along the Arabian Gulf coast.

Key Words: Red Sea, Remote Sensing, Mangroves, Infrastructure

Development, Image Registration, Normalized Difference Vegetation Index (NDVI)

Introduction

Mangroves are trees and shrubs that grow in brackish to saline coastal environments in the tropics normally between latitudes 25° N and 25° S. They belong to the plant family Rhizophoraceae and along the Red Sea coast of Saudi Arabia Avicennia marina is the dominant species but Rhizophora mucronata too occurs in patches. They occur in inter-tidal zones, estuaries and offshore islands. Mangroves protect coastal areas from erosion, storm surges, hurricanes and tsunamis their massive root system is efficient at dissipating wave energy. The unique ecosystem found in the intricate mesh of mangrove roots offers a quiet marine habitat for diverse groups of organisms.

Mangrove habitats support marine and avian life in the Red Sea. These environments have been under stress because of overgrazing, cutting, pollution, physical modification of the coastal habitat, and land use change for quite some time. There is a need for their conservation. Mangroves occur along both east and west coasts of the Arabian Peninsula and early research on the mangrove ecology and distribution along the Red Sea coast of Saudi Arabia were by published by Vesey-FitzGerald (1955, 1957); Zahran (1974, 1980) and EESAL, 1983. Price et al. (1987) surveyed the mangal (mangroves and other associated communities of flora and fauna) ecology on several locations along the Saudi Arabian coast of the Red Sea. A detailed environmental assessment study along the Red Sea coast of Saudi Arabia by Price et al. (1998) found that mangroves were significantly more

Distribution of Mangroves along the Red Sea Coast: Kumar et al.

abundant at the coastal sites than offshore and on the southern latitudes than in the north.

A comprehensive report of PERSGA (The Regional Organization for the Conservation of the Environment of the Red Sea and Gulf of Aden) provides the current status of mangroves in the Red Sea and Gulf of Aden (Khalil, 2004). This report discusses various threats to mangroves due to camel grazing, cutting, pollution due to construction, industrialization and changes in land use and shrimp farming. It also recommends guidelines for conservation, rehabilitation and management of the mangroves in the region.

We are studying distribution of mangroves all along the Red Sea coast of the Arabian Peninsula. This paper is first part of our study that covers the geographical distribution of mangroves along the northern Red Sea coast of Saudi Arabia. A similar study was recently published by Khan and Kumar (2009) along the Arabian Gulf coast of Saudi Arabia and the United Arab Emirates. The distribution of mangroves along the RED sea coast is not continuous, instead occurs in patches. The main objective of this paper is to numerically show the geographic distribution of mangroves in the region and create a point of reference about their distribution for the year 2000-2001. This paper reports on patchy distribution of mangroves on twenty locations along the northern Saudi Arabian Red Sea coast (Fig. 1) using Lnadsat ETM images of the years 2000 and 2001 (Fig. 2).

Red Sea

Red Sea is a long and narrow body of water separating northeast Africa on the west with the Arabian Peninsula to the east (Fig. 1). It is connected with the Indian Ocean at its southern end through the Bab el Mandeb strait and Gulf of Aden and is the world's northernmost tropical sea. Its northern end is bifurcated into two narrow elongated bodies of water on both sides of the Sinai Peninsula. On the west side is the Gulf of Suez and on the east side is the Gulf of Aqaba. Some basic statistics about the Red Sea is given in Table 1.

Surface water temperatures are constant year round at 21–25 °C. The salinity is higher than the world average ~ 40 (ppt). This is due to (a) high rate of evaporation and very little precipitation (b) lack of significant rivers or streams draining into the sea, and (c) limited connection with the Indian Ocean, which has lower water salinity. The climate of the Red Sea is the result of two distinct monsoon seasons; a northeasterly monsoon and a southwesterly monsoon. The rainfall over the Red Sea and its coasts is extremely low averaging 0.06 m/year; the rain is mostly in the form of showers of short spells often associated with thunderstorms and occasionally with dust storms. In summer NW winds drive surface water south, whereas in winter the flow is reversed resulting in the inflow of water from the Gulf of Aden into the Red Sea. The net value of the latter predominates, resulting in an overall drift to the northern end of the Red Sea. Thus the prevailing north and northeastern winds influence the movement of water in the coastal inlets to the adjacent sabkhas, especially during storms. Winter mean sea level is 0.5 m higher than in summer. Some information used in this paper is taken from Wikipedia.



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Fig. 1: Study area along the northern Red Sea coast of Saudi Arabia.

Fig. 2: Locations of 20 study sites along the northern Red Sea coast of Saudi Arabia.


Table-1: Some basic statistics about the Red Sea

Length: ~2,250 km (79% of the eastern Red Sea with numerous coastal inlets)

Maximum Width: ~ 306–355 km (across Massawa in Eritrea)

Minimum Width: ~ 26–29 km (across Bab el Mandeb Strait in Yemen)

Average Width: ~ 280 km

Average Depth: ~ 490 m

Maximum Depth: ~2,211 m

Surface Area: 438-450 x 10² km²

Volume: 215–251 x 10³ km³

Approximately 40% of the Red Sea is <100 m and about 25% is < 50 m deep

About 15% of the Red Sea is over 1,000 m deep that forms the deep axial trough

Shelf breaks are marked by coral reefs

Continental slope has an irregular profile (series of steps down to ~500 m)

Centre of Red Sea has a narrow trough (~ 1,000 m; exceeding 2,500 m)

Materials and methods

The study area is located along the northern Saudi Arabian Red Sea coast from Sharm Zubair in the north to Al-Lith in the south between Latitudes 27o 26' 00"and 20o 09' 00" (Fig. 2). Historical Landsat Enhanced Thematic Mapper (ETM) data of the years 2000 and 2001 were used (Table-2). The ETM data has seven spectral bands (Table-3). The spatial resolution of ETM data is 28.5 meters.

Table-2: Satellite image data used in the study

Location Sensor Date

site-1 ETM 05-10-2001 site-2 ETM 05-10-2001 site-3 ETM 05-10-2001 site-4 ETM 10-07-2000 site-5 ETM 10-07-2000 site-6 ETM 10-07-2000 site-7 ETM 10-07-2000 site8 ETM 23-10-2000 site-9 ETM 23-10-2000 site-10 ETM 23-10-2000 site-11 ETM 23-10-2000 site-12 ETM 12-07-2000 site-13 ETM 12-07-2000 site-14 ETM 12-07-2000 site-15 ETM 01-11-2000 site-16 ETM 01-11-2000 site-17 ETM 01-11-2000 site-18 ETM 01-11-2000 site-19 ETM 01-11-2000 site-20 ETM 03-06-2000



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Table-3: Landsat spectral bands

Landsat 7

(ETM+

sensor)

Wavelength

(micrometers)

Band 1 0.45 - 0.515 Band 2 0.525 - 0.605 Band 3 0.63 - 0.69 Band 4 0.75 - 0.90 Band 5 1.55 - 1.75 Band 6 10.40 - 12.5 Band 7 2.09 - 2.35

Image processing:

Satellite images and geographic information systems are useful tools to detect and compute aerial distribution of mangroves (Long and Skewes, 1996; Riaza et al., 1998; Verstraete et al., 2008). The first step in the processing of remotely sensed images is the geometric correction (Richards, 1986). In this study map-to-image ground control points were used to geometrically rectify all of the Landsat ETM data to UTM, WGS84 coordinates. All the images were radiometrically corrected using dark-pixel subtraction (Crane, 1971), also known as histogram minimum method (Chavez et al., 1977).

The second step in the processing of the satellite images is to exclude irrelevant land and water areas that can be readily identified as non mangroves habitats. This was accomplished by creating region masks by visual interpretation of color composites of Landsat ETM bands 4, 2 and 1, and high resolution Google Earth images (Manson et al., 2001). The coastal vegetation and algal mats were also excluded from the ETM images by creating region masks using ETM color composite of bands 4, 5 and 1, where vegetation species can be differentiated by their color and tone variations (Coleman et al., 1990). The vegetation associated with the mangroves such as halophytes which are mingled with mangroves and also has similar spectral signature may not have been excluded.

The most widely used technique for mapping vegetation with remotely sensed images is the Normalized Difference Vegetation Index (NDVI). Studies using NDVI and other vegetation indices are varied and include those involved with local, regional, and global mapping of vegetation (Townsend and Justice, 1986; Choudhury and Tucker, 1987; Jackson and Huete, 1991; Justice et al., 1991; Tucker et al., 1991; Richardson and Evert, 1992). Recently, Helldén and Tottrup (2008) used time series of annually integrated and standardized annual NDVI anomalies to study trends in regional desertification and suggested that this methodology is a robust and reliable way to assess and monitor vegetation trends and related desertification on a regional-global scale.

The Normalized Difference Vegetation Index (NDVI) is defined as:

NDVI = (RIR-R) / (RIR+R)

Where RIR = Reflective Infrared band (MSS bands 6 and 7; TM band 4)

And R = Red band (MSS band 5; TM band 3)


The masked Landsat ETM images were used to create NDVI images. NDVI for Landsat ETM images was calculated using bands 3 (0.63-0.69 µm) and 4(0.76-0.90 µm).

Results and discussion

In Landsat images the red band records the absorption of red wavelength by chlorophyll; lower values indicate higher chlorophyll. Reflected Infrared (RIR) band records the reflection of IR wavelengths by the cell structures of leaves; higher values indicate more vigorous growth (Richardson and Evert, 1992). Values of NDVI images ranged from -1.0 to 1.0. Higher values indicate higher concentrations of vegetation, which in this study are mangrove stands. Lower values indicate non-vegetated regions like water bodies and bare soil. Thresholds of NDVI greater than 0.1, were applied to the NDVI images to classify the mangrove stands in the images. The threshold criteria, was determined from the false color composites of two visible and one near infrared bands. In this color composite vegetation appears in hues of red and can be easily differentiated from bare land, mud flats and water bodies along the coastal regions. The familiarity with the area and known locations of mangroves were also helpful in determining the threshold boundary.

Fig. 3 through 22 show images of geographical distribution and area of mangrove forests at sites 1 through 20 respectively (Table-4). Their distribution is patchy and the areas covered by various mangrove stands vary considerably. They do not occur as a continuous forest and mostly their distribution is restricted to the quieter environments, for example, bays, narrow channels, and inland face of offshore islands. However, not all mangroves occupy quieter environments they inhabit higher energy intertidal environments also. At places they occupy very small area, for example, locations, 1, 3, 6 and 8 which could be a sign of depletion due to changes in land use and pollution. The Red Sea coastal regions of Saudi Arabia are witnessing rapid changes in urbanization and industrialization altering the traditional land use. These factors and pollution are adversely impacting the mangrove cover in the region.

The result of this study indicates that a variety of human activities in the

region are adversely impacting the mangrove forests. It is advised that due caution is required to protect the mangroves while planning for any economic and developmental activity. This can be achieved as shown by Khan and Kumar (2009) in their study of the mangroves of the Arabian Gulf coast where with in a span of thirty years’ of ‘developmental’ activities mangroves were depleted but in few cases mangroves grew more along with all the development al activities. Thus there is a need for clear policy to protect mangroves along with any developmental activity that takes place in the region.



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Fig. 3: Satellite image of mangroves shown in green color at site 1.











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Fig. 16 a: Satellite image of mangroves shown in green color at site 14 (Red circle shows the location of photograph in Fig. 16b).

Fig. 16 b: Study site14 (red circle in Fig. 16 a): A recent view of mangrove stands close to the Red Sea coastline near Petro-Rabigh in Rbigh.




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Table-4: Area of mangrove forests (hectares) at the twenty locations along with their latitude and environmental setting

Site Latitude

(range)

(Deg. Min. Sec.)

Mangrove

area

(Hectares)

Environment

1 27 26 03 4.3 Bay

2

26 56 34 to 26 54 11

21.5 Channel between mainland and nearshore island

3 26 38 07 0.6 Bay

4 26 21 06 to 25 55 40

36.1 Intertidal

5 25 54 41 to 25 22 00

661.9 Landward side of the nearshore island

6 25 18 24 2.8 Intertidal 7 24 48 02 10.1 Bay 8 24 11 57 8.5 Bay

9 24 00 27 to 23 57 16

121.0 Bays and intertidal

10 23 57 04 to 23 54 26

125.2 Intertidal

11 23 21 16 to 23 19 40

22.9 Bays

12 23 09 19 to 23 07 38


13 22 58 22 to 22 50 39

136.7 Island with in the bay

14 22 45 40 to 22 45 07

13.6 Bay

15 22 23 52 to 22 12 50


16 22 09 42 to 21 59 55


17 21 23 36 to 21 22 06

11.4 Landward side of the nearshore island

18 20 49 44 to 20 44 27

166.7 Bay

19 20 32 59 to 20 32 22

23.9 Bay

20 20 17 59 to 20 09 32

418.0 Island with in the bay

Conclusions

1. The distribution of mangroves along the northern regions of the Red Sea coast of Saudi Arabia is patchy and they do not occur as a continuous forest.

2. Mostly their distribution is restricted to the quieter environments, for example, bays, narrow channels, and inland face of offshore islands.

3. Mangroves also inhabit intertidal environments. 4. At places they occupy very small area, for example, locations, 1, 3, 6

and 8. This could be a sign of depletion due to changes in land use and pollution.








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5. The Red Sea coastal regions of Saudi Arabia are witnessing rapid changes in urbanization and industrialization leading to alteration in the traditional land use. This is adversely impacting the mangrove cover in the region.

6. It is advised that due caution is required to protect the mangroves while planning for any economic and developmental activity. This can be achieved as shown by Khan and Kumar (2009).

Acknowledgements: We thank King Fahd University of Petroleum and Minerals (KFUPM), Dhahran, Saudi Arabia for permission to publish this paper.

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About the authors

Dr. Arun Kumar is a Research Scientist and Professor at the Center for Petroleum and Minerals, Research Institute, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia. He obtained his Ph.D. (Stratigraphic Palynology) from Michigan State University, USA and a second Ph.D. (Environmental Micropalaeontology) from Carleton University, Canada. Dr. Kumar taught geology at Kumaun University, Nainital, India, University of the West Indies, Kingston, Jamaica, Carleton University and Concordia University (Montreal) in Canada. He also worked as a geologist and palynologist with Oil and Natural Gas Corporation of India and Core Laboratories International (USA) in Singapore and Jakarta, Indonesia. Dr. Kumar has published extensively on Mesozoic and Cenozoic pollen, spores and dinoflagellate cysts, environmental applications of thecamoebians, benthic foraminifera as paleoclimate and paleoceanographic proxies, and on current environmental issues. His new research interest is in natural hazards and environmental issues. *corresponding Author

Mr. Muhammad Asif Khan is a Research Specialist II (Associate Professor) in the Remote Sensing unit, Center for Petroleum and Minerals, The Research Institute, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia. At the Research Institute, he established Remote Sensing Facility in 1982 which was the first of its kind in the entire Middle East. He has also participated in leading edge international experiments in remote sensing and authored numerous refereed research papers and technical reports.

Mr. Abdul Muqtadir is a Scientist III in the Image Processing Lab, Center for Petroleum & Minerals of the Research Institute. He received a Professional Diploma in Electronic Data Processing (EDP) from Aligarh Muslim University, Aligarh, India in 1978. Earlier, he also worked with Toyo Engineering Corporation, Schwedt, Germany. Mr. Muqtadir is providing data handling and database management support in a number of projects related to remote sensing applications, GIS and sand studies.

Documents

Distribution of Mangroves along the Red Sea Coast of the ... · Mangrove habitats support marine and avian life in the Red Sea. ... This paper is first part of our study that covers