Integrated Field Studies and Remote Sensing Approach for Mapping Seagrasses and Mangrove Habitats, Red Sea, Egypt.

Abstract

Seagrasses and mangroves represent the main producers in the marine habitats and their importance extended to marine organisms and terrestrial ones and provides high values of goods and services to humanity. Hurghada and Safaga at the Red Sea Coast, have witnessed over the past few decades, a lot of anthropogenic activities which affected certainly on these habitats. Clearly, these habitats didn't found the appropriate attention from botanists. In addition to the field monitoring, Remote Sensing techniques was applied successfully for monitoring and mapping the terrestrial and aquatic egetation. Therefore, the current study aimed to integrate between field study and Remote Sensing Technique in monitoring and mapping seagrasses growing in Hurghada and Safaga and detect the periodical changes in these habitats as well as to assess using the seagrasses beds as biomonitoring agent for heavy metals pollution in coastal zone of Hurghada and Safaga was also investigated. Five seagrasses were identified in the 41 stands; Halophila stipulacea (Forssk.) Asch., Halodule uninervis (Forssk.) Boiss., Halophila ovals (R.Br.) Hook. f., Thalassodendron ciliatum (Forssk.) Hartog and Syringodium isoetifolium (Forssk.) Hartog. All recorded seagrasses are belonging to tropical indo-pacific bioregion. Application of TWINSPAN and DECORANA, as classification and ordination techniques to the 41 stands resulted in five vegetation groups. Integration between field data and satellite images resulted in mapping seagrass and mangrove sites and the coverage area of each seagrass species and the total coverage area of seagrass beds and mangrove forests along the Red Sea coast. Results indicated that H. uninervis represents the dominant seagrasses in Hurghada and Safaga according to its spatial distribution and coverage area. Satellite images showed that seagrass beds coverage areas were reduced by 69.8% in Hurghada and 25.4% in Safaga. Mangrove coverage area shows drastic reduction by 98.65% in Um Dehais and 52.7% in Km-17 S. Safaga. The net mangrove coverage area in Abu Minqar (Hurghada) and Sharm El Bahari (Qusier) increased by 59.6 and 127.2% respectively. All sites in Hurghada, Safaga and Qusier showed reduction in their mangrove coverage areas in the period 1990-2002. Seawater contains low concentrations of heavy metals in the study sites dominated by Fe and followed the orders; Fe>Mn>Cu>Pb>Zn>Cd, or Fe>Cu>Mn>Pb>Zn>Cd. Fine sediment granules (Ø3, Ø4 and Ø5) had the highest percentage ranged from 62.91 to 92.20% than other granules in the study sites. Highest percentage of silicates and total organic matter were recorded in Safaga Fishing Port site (SFP) while that of carbonates were recorded in Wadi Quiah. Noticeably, high fluctuation in the concentrations of each heavy metal in the same site indicate variation in heavy metals resources. Iron is the main metal in the fine fractions of sediments. The dominant order of heavy metals in the fine granules of the sediments in the studied sites was Fe>Zn>Mn>Cu>Pb>Cd. These results showed that SFP sediment contains highest concentrations for the most heavy metals. In parallel to fluctuation of heavy metals in sediment high fluctuation of heavy metals concentrations were recorded in each seagrass part at the same site.