Abstract
Al-Kharrar Lagoon is a fossil back-reef basin with hypersaline waters, situated 10 km northwest of Rabigh city, central of the eastern Red Sea coast, Saudi Arabia. About 130 stations were selected for measurements of the lagoon's water temperature, salinity, pH, dissolved oxygen, and water depths during March 2014. The common macro-algae, flora, and fauna were also sampled and identified. The present study aims to investigate the prevailing environmental parameters and their impact on the macro-fauna/flora of the lagoon. The average water depth of the lagoon was around 5 m and reached maximum values of 8 and 16 at the lagoon centre and inlet, respectively. The results showed that the lagoon's surface water temperature and salinity have mean values of 25 degrees C and 40%, but with extreme values of 30 degrees C and 45% that occurred only at the enclosed intertidal areas, respectively. Their dissolved oxygen (DO) and pH were 6.5 mg/ l and 8.3, respectively and the latter showing the highest values up to 8.5 in the intertidal areas dominated by the green cyanobacteria. These physicochemical conditions make the lagoon as a favorite place for the mangrove Avicennia marina, macro-algae, seagrasses (Halophila stipulacea and Cymodocea rotundata), and algal mats (Cyanobacteria) which dominate the intertidal and supratidal areas of the lagoon, tolerating extremely high-salinity and high-temperature conditions. On the other hand, corals were observed alive at the southern part of the lagoon, immediately south of the Al-Ultah Islet. Vertical profiles of temperature, salinity, and density in the lagoon's water indicated that the water column consists of two layers throughout the year.