ECOLOGY AND BLOOM-FORMING ALGAE OF A SEMI-PERMANENT RAIN-FED POOL AT AL-KHARJ, SAUDI-ARABIA

An account of seasonal succession of bloom-forming algae over a period of 3 consecutive years (1992-1995) is described in relation to the tr ophic changes taking place in a semi-permanent rain-fed pool at Al-Kha rj, Saudi Arabia. Population dynamics from the two contrasting arid ec osystems show varied degrees of changes in water chemistry and algal f lora. Recovery of algal blooms after a few flashflood events can be de scribed as a model of temporal succession in the semi-permanent/desicc ated water body. Morphometric properties and mesotrophic planktonic bi ota were restored within 2-3 weeks of rainfall (5-10 cm water deposite d). The dominant and the first to emerge was the bloom-forming green a lga Carteria multifilis followed by Micratinium pusillum. A gradient s easonal succession from relatively mesotrophic to hypertrophic was rec orded. Subsequently, the blue-green algae Oscillatoria limnetica and M icrocystis aeruginosa succeeded resulting in bluish-green to drab oliv e colourization to the water. Altogether, 32 species are reported, c. 30% of which are newly recorded to the Saudi Arabian algal flora. Emer gence and survival of consistent flora was positively correlated with water quality and seasonal succession. (C) 1998 Academic Press Limited .