A review of seagrass studies by using satellite remote sensing data in the southeast asia: Status and potential - Nguyen Thi Thien Huong

Vietnam Journal of Science and Technology 55 (4C) (2017) 148-154 A REVIEW OF SEAGRASS STUDIES BY USING SATELLITE REMOTE SENSING DATA IN THE SOUTHEAST ASIA: STATUS AND POTENTIAL Nguyen Thi Thien Huong 1 , Tran Anh Tuan 2 , Vo Trong Thach 3 , Hoang Cong Tin 2, * 1 Centre for Coastal Management and Development Studies, University of Sciences, Hue University, 77 Nguyen Hue Street, Hue city, Thua Thien Hue province, Viet Nam 2 Faculty of Environmental Science, University of Sciences, Hue University, 77 Nguyen Hue Street, Hue city, Thua Thien Hue province, Viet Nam 3 Nhatrang Institute of Technology Research and Application, VAST, 02 Hung Vuong Street, Nha Trang city, Khanh Hoa province, Viet Nam * Email: hoangcongtin@gmail.com Received: 30 June 2017; Accepted for publication: 16 October 2017 ABSTRACT This review presents synthetic results of remote sensing application in monitoring and management of seagrass beds in the Southeast Asia region. The objective of this paper aims to evaluate the status and potential of using remote sensing technologies in seagrass mapping to enhance its effective utilization and management. The results showed that the number of studies in the application of remote sensing for seagrass are still limited, mainly from 2011 to 2017, which focus on habitat mapping (accounting for 62 %) and other studies on the detection of seagrass change in temporal (38 %). The number of studies on using medium and high resolution remote sensing images are approximately about 50 % and 44 %, respectively. Only 6 % studies used very high resolution remote sensing images. Finally, it is suggested that having more study in seagrass bed mapping by using remote sensing data is significant for understanding the variability of seagrass beds in the coastal areas for effective management and protection in the future. Keywords: remote sensing, seagrass, Southeast Asia region. 1. INTRODUCTION Seagrasses are the aquatic flowering plants that widely distribute in coastal brackish lagoons, bays, estuaries and nearshore of the islands. They actually play an important role in coastal ecosystems and human [1 - 7]. However, the degradation of seagrass beds has been seriously occurred, especially in the Southeast Asia countries [4, 7, 8]. The main reason of this decline was human’s activities and partly natural disasters [9 - 12].The remote sensing data can provide information for assessing the evolution of the coastal ecosystems in the past, describing the status and predicting trends for their dynamics in the future [13]. The detection of seagrass changes by using satellite remote sensing data contributes significantly to management and monitoring of Seagrass studies by using satellite remote sensing data in the Southeast Asia 149 coastal and marine ecosystems. The spatial distribution data and qualitative characteristics of habitats can be considered as the basic and essential information that help us to understand and protect the ecosystems from impacts of human and nature [13 - 15]. Therefore, the application of remote sensing data in mapping and finding the habitat’s change has become a vital tool for assessing and monitoring coastal ecosystems as well as supporting for constructed spatial planning of coastal works [9, 13, 15]. Based on that, this study was conducted with three objectives: i) Synthetic study the resources distribution and current status of seagrass in the Southeast Asia; ii) The results of this study showed a general picture of seagrass studies by using the remote sensing images and GIS technology in Southeast Asia countries has taken; and iii) Which research direction should be further developed in the future to monitor and manage effectively seagrass resources. 2. METHODS This review focused on papers that used satellite remote sensing data to monitoring and mapping seagrass beds in the Southeast Asian countries. The approach applied for the published articles which were collected in two main data resources including ScienceDirect (www.sciencedirect.com) and ResearchGate (www.researchgate.net). ScienceDirect is a website which ran by the Elsevier publisher in the UK-Holland. This is one of the largest libraries in the world for scientific journals and magazines with all majors established in March 1997 with approximately 2,500 scientific journals and more than 26,000 e-books. ResearchGate is the most popular website in the world today for scientists in order to connect researchers each other and promote the exchange of results, knowledge and experiences. The published articles in the ResearchGate were issued in the domestic and foreign scientific journals. In addition, this paper also referred to four referencing books on seagrass composition species and resources in Vietnam, Indonesia, Malaysia, Thailand; and a book on satellite remote sensing. Of the 35 articles used in this paper, 16 articles on remote sensing application were used to map seagrass distribution and variation in Southeast Asia countries, the remaining articles on seagrass resources (17 articles) and remote sensing studied review for seagrass (2 articles). Terms and keywords such as “Seagrass mapping”, “Southeast Asia”, and “Remote Sensing” were used individually to search the related papers from two main databases. We classified the published studies into two groups based on whether they apply remote sensing imagery in seagrass study. This review only focused on published research articles in international journals. It is noted that our literature search did not include projects’ summary and technical reports of the topics that have not yet been published in prestigious journals.In term of the classification spatial resolution, remote sensing images was divided based on Samantha & Lavender, 2015 report [32]. Microsoft Excel 2013 used for data storing and processing. 3. RESULTS AND DISCUSSION 3.1. Characteristics of seagrasses in the Southeast Asia countries Located in the tropical region, the Southeast Asia has a number of abundant seagrasses with 20 seagrass species out of 72 species in the world (accounting 28 %) and the distribution area of more than 3.1 million hectares [5 - 7, 16 - 19]. Indonesia is the country that had the largest seagrass area with approximately 3 millions hectares [5] whereas seagrass’ distribution area in Singapore was the least with 40 hectares [17]. So far, we could not find any literatures Nguyen Thi Thien Huong, Tran Anh Tuan, Vo Trong Thach, Hoang Cong Tin 150 documented the distribution area of seagrass in Myanmar. In the coastal areas of Vietnam, 16 seagrass species have been identified with a distribution area approximately 18,130 ha [7]. However, the distribution area of seagrasses in Vietnam have tended to seriously reduce in temporal scale [10 - 12, 20, 21]. Recently, seagrasses in the Southeast Asia have dramatically declined. The distribution area of seagrass was reduced about 30 - 50 % in Indonesia and Philippines [1, 4, 8]; 20 - 30 % in Thailand [1]. In Vietnam, the distribution area of seagrass reduced 45.4 % in the last two decades and the average loss rate of the whole country was 4.4 % per year [1]. The declining reasons included human activities such as fishing, boat mooring caused the erosion of seagrass beds in coastal areas; aquaculture and environmental pollution increases the turbidity of water which leading to seagrass growth very slowly; port constructive activities; land reclamation for building accommodations and tourism facilities led to the loss of seagrass beds [4, 8, 23]. Besides, natural disasters such as tropical typhoons, coastal floods and turbidity also influenced seagrass beds [9 - 12]. 3.2. Seagrass monitoring and management by using remote sensing imagery 3.2.1. Research situation in the Southeast Asia countries The studies of mapping and analyzing of seagrass change using of remote sensing images in the Southeast Asia countries are still limited. According to our statistics, each country in the Southeast Asian countries has only 1-3 seagrass studies using remote sensing imagery (Table 1). At present, we have not found any published literatures of the remote sensing imagery application in seagrass studies in Indonesia and Singapore. Table 1. Seagrass studies by using remote sensing image in the Southeast Asian countries. Country Authors/Sources RS satellite images Results Cambodia Sophany et al., 2012 [22] ALOS AVNIR-2 Maps Indonesia Not available [23]. Not available Not available Malaysia Abd. Wahid et al., 1997 [24] Landsat-5 Maps Mohd et al., 2015 [25] ALOS AVNIR-2; Quickbird Maps Hossaina et al., 2015 [26] Landsat-5, 7, 8 Seagrass changes Myanmar Claudia et al., 2016 [27]. Landsat-8 Maps Philippines Ayin et al., 2013 [8]. WorldView-2 Maps Blanco et al., 2014 [16]. Landsat-7, 8 Seagrass changes Singapore Not available Not available Not available Thailand Werapong et al., 2016 [28]. WorldView-2 Maps Satomi et al., 2016 [29]. Landsat-8 Maps 3.2.2. Research situation in Vietnam In Vietnam, the application of remote sensing imagery and GIS technology on seagrass research has only been implemented since 2009 with five typical studies that are presented in the Table 2. One of the first study related to this research topic which was conducted by Cao et al. [9] using remote sensing images and GIS technology in seagrass mapping in Vietnam coast. The Seagrass studies by using satellite remote sensing data in the Southeast Asia 151 results showed that seagrass area in Vietnam was 17,000 hectares. Seagrass distribution was sharply declined (over 50 %) compared to the period 10-15 years ago. Several seagrass beds in Quang Ninh, Hai Phong and Phu Quoc provinces were almost lost. The seagrass beds in the Tam Giang – Cau Hai lagoons and Cua Dai estuary in 2009 decreased by 50-70 % compared to the 1990s [11]. The cause of the degradation was mainly affected by natural factors (e.g. tropical typhoons, high turbidity) as well as human impacts (e.g. destructive fishing, oil spills, and aquaculture activities). Remote sensing data such as ALOS AVNIR-I, AVNIR-II, Landsat TM and SPOT 5 were used to map and compare changes of seagrass distribution [9]. Table 2. Seagrass studies using remote sensing image in Viet Nam. Sources Research site Research period RS images Results Cao et al. [9,10] Vietnam coast 1999-2009 AVNIR-I, II; Landsat, SPOT 5 Map and compare changes of seagrass Hoang et al. [13,30] T.T. Hue province 2011 AVNIR-2 Seagrass map Ha et al. [31] T.T. Hue province 2012 AVNIR-2 Seagrass map Phan et al. [12] Khanh Hoa province 2012 Landsat, SPOT, LOS AVNIR-2 Maps Chin-Farn et al. [2] Khanh Hoa province 2016 Landsat Seagrass changes 3.3. Potentials of remote sensing application in the seagrass beds management The remote sensing imagery resources are divided into three groups: medium spatial resolution images (MSR) (1 km – 30 m), high spatial resolution images (HSR) (< 30 m) and very high resolution images (VHSR) (< 1 m) [32]. It can be seen that, about 50 % of MSR, 44 % of HSR and 6 % of VHSR were used in seagrass studies in the Southeast Asia countries. Remote sensing application for studying in seagrass change in temporal is still relatively small, with only 38 % of the studies, mainly using the remote sensing images for mapping (62 %) (Figure 1). Figure 1. A-Proportion of remote sensing images using seagrass researches; B-Proportion of the purpose of remote sensing use. HSR, MSR, VHSR are high, medium, very high spatial resolution images, respectively. Among typical studies in the Southeast Asia region of which two studies were conducted by Hossaina et al. [26] in Malaysia and Chi-Farn et al. [2] in Vietnam. This opened up new potential for the further seagrass researches by using remote sensing images. In particular, the study of Hossain et al. presented the reasons given seagrass’s degradation. Therefore, it is essential to find solutions for restore and preserve the seagrass beds. Chi-Farn et al. used the remote sensing images from 1996 to 2005 to find seagrass changes in temporal, thereby predicting seagrass changes in the future and recommending effective and sustainable management measures. 44% 50% 6% HSR MSR VHSR Seagrass mapping 62% Seagrass changes 38% B A Nguyen Thi Thien Huong, Tran Anh Tuan, Vo Trong Thach, Hoang Cong Tin 152 4. CONCLUSIONS The application of remote sensing images and GIS technology in mapping and analyzing of seagrass changes in the Southeast Asian countries are generally limited. Only few studies conducted in Cambodia, Myanmar, Malaysia, Philippines, Vietnam, and Thailand. Up-to-date, there has not any published documents related to the remote sensing imagery for seagrass mapping in Indonesia and Singapore. Southeast Asian region has more than 3 million hectares of seagrass. Therefore, a comprehensive seagrass study program by using satellite remote sensing and GIS technology is required in order to propose an efficient management and sustainable utilizing measures of seagrass resources. Future research efforts could be focused on (i) Using remote sensing images to evaluate temporal changes of seagrass beds in the Southeast Asian countries; (ii) Determining the cause of seagrasses changes; and (iii) Proposing measures for sustainable management and protection of seagrass beds in the Southeast Asian countries. Acknowledgements. The authors acknowledge the national project on space science and technology period of 2016-2020 (VT-UD.01/17-20) and the Kyoto University Graduate School of Global Environmental Studies (GSGES) for the encouragement and financial support. REFERENCES 1. Nguyen V. T., N. D. Thanh, Nguyen H. D. - Vietnamese Seagrasses, The Sciences and Technology Press - Ha Noi, 2002, pp. 165 (in Vietnamese). 2. Chi-Farn C., Va-Khin L., Ni-Bin C., Nguyen-Thanh S., Phuoc-Hoang-Son T., Shou-Hao C. - Multi-temporal change detection of seagrass beds using integrated Landsat TM/ETM + /OLI imageries in Cam Ranh Bay, Vietnam. Ecological Informatics 35 (2016) 43-54. 3. Frederick T., Short C.A., and Robert G. C. - In Global Seagrass Research Methods, Coles R.G., , Elsevier Science: Amsterdam, 2001, pp. 250. 4. Nadiarti, Etty R., Ita D., Sugeng B., Ari P., Harald A. - Challenging for seagrass management in Indonesia. Journal of Coastal Development 15 (3) (2012) 234-242. 5. Ogawa H., Japar S. B., Muta H. Z., Nihon G. S., To kyo D., Taiki K. K. - Seagrasses: Resource status and trends in Indonesia, Japan, Malaysia, Thailand and Vietnam, Tokyo: Seizando-Shoten Publishing, 2011, pp. 165. 6. Ouk V., So N., Lim P., Pich S. W. - Seagrass diversity and distribution in coastal area of Kampot province, Cambodia. International Journal of Environmental and Rural Development 1-2 (2010) 112-117. 7. Nguyen V. T. - The resource of Vietnamese seagrass beds, Ha Noi, 2013, pp. 337 (in Vietnamese). 8. Ayin M. Tamondong et al. - Mapping of seagrass and other benthic habitats in Bolinao, Pangasinan using Worldview-2 satellite image. Geoscience and Remote Sensing Symposium (IGARSS) 14058802 (2013) 1579-1582. 9. Cao V. L., Nguyen V. T., Teruhisa K., Nguyen D. V., Dam D. T. - Status and threats on seagrass beds using GIS in Vietnam. Remote Sensing of the Marine Environment II 8525 (2012) 1-13. 10. Cao V. L. - The status of seagrass beds in Cua Dai (Hoi An, Quang Nam). The collection of Marine Resources and Environment XVI (2011) 144-150 (in Vietnamese). Seagrass studies by using satellite remote sensing data in the Southeast Asia 153 11. Nguyen X. H., Nguyen N. N. T. - The status and changing trend of mangroves and seagrasses at Van Phong Bay, Khanh Hoa province, The collection of Marine Research 20 (2014) 135-147 (in Vietnamese). 12. Phan M. T., Son H. T. P., and Komatsu T. - Using remote sensing technique for analyzing temporal changes of seagrass beds by human impacts in waters of Cam Ranh Bay, Vietnam in Remote sensing of the marine environment II 8525 (2012) 1-8. 13. Hoang C. T., Tong P. H. S. - Application of satellite remote sensing data on mapping Vietnamese coastal ecosystems, The proceeding of international conference on Bien Dong 2012, Nha Trang, 2013, 324-333 (in Vietnamese). 14. John D. H., Chris M. R., Iliana C., Alastair R. H., Scott F. H., Scarla W., William J. S., Alan E. S., Mark E., Tyler R. L. C., Victor T., Sonia B., Peter J. M. - Remote Sensing of Coral Reefs for Monitoring and Management: A Review. Remote Sensing 8 (2) (2016) 1-40. 15. Hossain M.S., Bujang J.S., Zakaria M.H., Hashim M. - The application of remote sensing to seagrass ecosystems: an overview and future research prospects. International Journal of Remote Sensing 36 (1) (2015) 61-114. 16. Blanco A.C., Tamondong A., Tagle E., Fortes M., Nadaoka K. - Change in seagrass fractional cover in Bolinao and Anda, Philippines derived from landsat images, Asian association on remote sensing, Myanmar, 2014, 370-376. 17. Len J. M., Siti M. Y., Ria T., Jamie S., Rudi L. Y. - Seagrass habitats of Singapore: Environmental drivers and key processes, Affles Bulletin of Zoology 54 (2016) 60-77. 18. Soe-Htun U., Mya K. W., Thida N., Soe P. P. K., Mu M. A. -Notes on seagrasses along Myanmar coastal regions. Bulletin of Marine Sciences and Fisheries, Kochi University 21 (2001), 13-22. 19. Vibol, O. - National report on seagrass in the South China Sea, Cambodia 2008, pp. 207. 20. Cao V. L. - The status of seagrass beds in Tam Giang – Cau Hai lagoon system (Thua Thien Hue province), The proceeding of the fifth national conference on marine science and technology, The Sciences and Technology Press - Ha Noi, 2011, pp. 312-318 (in Vietnamese). 21. Cao V. L., Dam D. T., Nguyen C. T. - The status of seagrass in the western of Gulf of Tonkin, Journal of Marine Science and Technology 14 (3A) (2014) 223-229 (in Vietnamese). 22. Sophany P., Teruhisa K., Shuhei S., Thidarat N. -Marine habitat mapping: Using ALOS AVNIR-2 satellite image for seagrass beds at Rabbit (Koh Tonsay) Island, Cambodia. Proceedings of SPIE - The International Society for Optical Engineering 8525 (2012) 1-6. 23. Nadiarti, Etty R., Ita D., Sugeng B., Ari P., Harald A. - Challenging for seagrass management in Indonesia, Journal of Coastal Development 15 (3) (2012) 234-242. 24. Abd. Wahid R., Hashim M. - Mapping seagrass from satellite remote sensing data, The proceeding of Asian Conference on Remote sensing 1997, 1-4 25. Mohd I. S. M., Nurul N. Y., Samsudin A., Teruhisa K., Tetsuo Y. - Sea bottom mapping from ALOS AVNIR-2 and Quickbird satellite data, 2015, 1-14. Nguyen Thi Thien Huong, Tran Anh Tuan, Vo Trong Thach, Hoang Cong Tin 154 26. Hossaina M. S., Bujangb J. S., Zakariac M. H., Hashim M. - Application of Landsat images to seagrass areal cover change analysis for Lawas, Terengganu and Kelantan of Malaysia, Continental Shelf Research 110 (2015) 124-148. 27. Claudia G., Mariano B., Francesco F., Erica M., Vittorio E. B., Roberto C. -Mapping Submerged Habitats and Mangroves of Lampi Island Marine National Park (Myanmar) from in situ and Satellite Observations, Remote Sensing 8 (2) (2016) 1-13. 28. Werapong K., Wissarut I., Raymond J. R., Alfredo H. - An integrated field and remote sensing method for mapping seagrass species, cover, and biomass in southern Thailand, Remote Sensing 8 (4) (2016) 1-18. 29. Satomi K., Takeuchi W., Prathep A. - Seaweed and seagrass mapping in Thailand measured by using Landsat 8 optical and texture properties, Journal of Marine Science and Technology 24 (6) (2016) 1155-1160. 30. Hoang C. T., Ton T. P., Nguyen Q. T. - Application of satellite remote sensing and geographic information system (GIS) on accessment of seagrass beds at Huong Phong coastal wetland, Huong Tra district, Thua Thien Hue province, HU-Journal of Sciences (65) (2011) 231-239 (in Vietnamese). 31. Ha N. T., Yoshino K., Son H. T. P. - Seagrass mapping using ALOS AVNIR-2 data in Lap An Lagoon, Thua Thien Hue, Viet Nam,Remote Sensing of the Marine Environment II 8525 (2012) 1-9. 32. Samantha L., Lavender A., Practical Handbookof Remote Sensing, CRC Press, Taylor & Francis Group, USA, 2015, pp. 212.