Tolerance of Benthic Diatoms to Severe Environmental Stress: A Case Study in Shatt Al-Arab River, Basrah, Iraq

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.