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 trophic changes taking place in a semi-permanent rain-fed pool at Al-Kharj, Saudi Arabia. Population dynamics from the two contrasting arid ecosystems show varied degrees of changes in water chemistry and algal flora. Recovery of algal blooms after a few flashflood events can be described as a model of temporal succession in the semi-permanent/desiccated water body. Morphometric properties and mesotrophic planktonic biota were restored within 2–3 weeks of rainfall (5–10 cm water deposited). The dominant and the first to emerge was the bloom-forming green algaCarteria multifilisfollowed byMicractinium pusillum. A gradient seasonal succession from relatively mesotrophic to hypertrophic was recorded. Subsequently, the blue-green algaeOscillatoria limneticaandMicrocystis aeruginosasucceeded resulting in bluish-green to drab olive colourization to the water. Altogether, 32 species are reported,c. 30% of which are newly recorded to the Saudi Arabian algal flora. Emergence and survival of consistent flora was positively correlated with water quality and seasonal succession