Composition of blue-green algal mats and water chemistry of the Bani Malik hot spring (Gizan Province), Saudi Arabia.

ABSRACT he ecology of microbial mats, water chemistry and invertebrates in the Bani Malik hot spring sizan Province) Saudi Arabia are presented. Various forms of thick algal mats were identified. hey exhibited significant growths and occurred in a temperature gradient (45-50°C) in a atural stream. An abundance of Phormidium/Oscillatoria, Srnechococcus lividus and alothrix/Pleurocapsa occurred as visually-obvious mats. In the mats were discrete groupings ihich were recognizable by their morphologies and color discriminations. These outgrowths sere regarded as a nuisance by the area development authority. A community apparently notreviously recorded in the thermal springs of Saudi Arabia was abundant in a deep thermal This consisted of clusters of pedicellate nodular mats predominated by Calothrix thermalis 90%with the remainder contributed by Pleurocapsa minor (10%). A cross-section of the mat .evealed striking laminations composed of an outer thin cover (Svnechococcus spp followed a middle thick zone (Calothrix thermalis/Pleurocapsa minor) and finally a central zone (calcite crystals) of a rather firm consistency. The other biological structure consisted of intermittent old and dead filaments of C. thermalis, with a few insect larvae associated within the mat. The overwhelmingly lothic algal community in a hydrogen sulfide-rich thermal pool appeared to play an active role in the photosynthetic activity, resulting in aeration (02 = 3.5 mg/1) of the waterbody. The water may be characterized as slightly-to-moderately alkaline with high concentrations of reactive-Si (44 mg/1), Cl- (217 mg/1) and so2 - 4 (613 mg/I). The water of the spring orifice contained hydrogen sulfide (