Abstract
The ecology of microbial mats, water chemistry and invertebrates in the Bani Malik hot spring (Gizan Province) Saudi Arabia are presented. Various forms of thick algal mars were identified. They exhibited significant growths and occurred in a temperature gradient (45-50 degrees C) in a natural stream. An abundance of Phormidium/Oscillatoria, Synechococcus lividus and Calothrix/Pleurocapsa occurred as visually-obvious mats, In the mats were discrete groupings which were recognizable by their morphologies and color discriminations. These outgrowths were regarded as a nuisance by the area development authority. A community apparently not previously recorded in the thermal springs of Saudi Arabia was abundant in a deep thermal pool. 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 revealed striking laminations composed of an outer thin cover (Synechococcus spp.), followed by 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 (O-2 = 3.5 mg/l) of the waterbody.
The water may be characterized as slightly to-moderately alkaline with high concentrations of reactive-Si (44 mg/l), Cl- (217 mg/l) and SO2-4 (613 mg/l). The water of the spring orifice contained hydrogen sulfide (> 5 mg/l).