No abstract

The present work aims at investigating the ability of diatoms to re-establish their community after a severe environmental stress such desiccation. Diatoms were subjected to extreme environmental stress to observe their survival capability. Samples of sediment were collected from three sites, Maqal, Abu Flos and Al-Faw along the course of Shatt Al-Arab river. Different temperature regimes were implemented for testing the ability of diatoms to recover desiccation. Experiments were performed at various temperatures, 10, 15, 20, 25, 30, 35 and 40 ℃. A total of 67 diatom species were identified and included freshwater forms (25%), brackish water forms (25%) and marine species (26%), as well as 24% of taxa with undefined ecological preferences. The recovery rate of diatom species at all sites appeared to be rather similar. 40%, 38% and 37% of all taxa encountered were able to recover desiccation at sites 1, 2 and 3, respectively. Recovering ability of those species varies with variable temperature. Favourable temperature for most species to regrow ranged between 15 and 25 oC. Nitzschia palea exhibited the maximum growth rate at all temperatures (10-35 oC). 32% of all epiphytic species encountered were able to recover at 20 oC. Five species: Craspedostauros britannicus, Nitzschia invisitata, Pinnularia quadratarea, Simonsenia sp. and Tryblionella plana were not previously reported in Iraq and considered as new to the region. A new species, Synedropsis abuflosensis, was found. The outcome of the present work clearly indicates that some species of diatoms can recover after exposure to sever environmental stress.

The diatom genus Fallacia includes species having a conopeum which is a perforated thin sheath of silica lying along the apical axis on the external valve face and a hyaline lateral area in the internal valve face. In surveying the benthic diatoms of Basra, a new small brackish water species, Fallacia fawensis was found associated with fine-grained substrata on the western bank of Shatt Al–Arab River, Southern Iraq. This epipelic species is described based on light and scanning electron microscopy and characterized by having a porous conopeum covering the area between raphe sterna and mantle, narrow elongated marginal striae, and a structure similar to lateral hyaline areas in the valve internal side. The terminal raphe endings on the external valve face, below valve apex, the raphe sternum inner margins come close to each other, blocking raphe canal but leaving a lacuna-like thin groove for connection with the deflected upper part of the open raphe canal. These features separated this species from allied taxa of the genus and also from closely related genera, Pseudofallacia and Germaniella. Notes on the ecology and distribution of the new species as well as the associated diatom taxa are provided.