Article

In 26 samples of plankton and periphyton taken from nine stations on the Alexander River and one station on the tributary we found 145 species of algae and cyanoprokaryotes from seven divisions. Green algae strongly prevailed. Fifteen algal species are recorded for the first time in Israel. Among them Salpingorhiza pascheriana, Salpingoeca ringens, and Chrysocrinus irregularis (Chrysophyta) as well as Lepocinclis lefeèvrei (Euglenophyta) were widespread, but rare all over their ranges. As a whole, 129 species are indicators of environmental conditions. Onkonema compactum (Cyanoprokaryota) is an indicator of warm water habitats. A green filamentous alga Enteromorpha torta is an indicator of a strongly saline habitat. The group of pH indicators is dominated by oligohalobes-indifferents and alkaliphiles. Indicators of saprobity, according to Watanabe’s and Sládeèek’s methods, show a moderate level of organic pollution. Species richness in the algal communities over the stations of the Alexander River is changing from rich communities with 6 divisions in the upper reaches to poor communities of cyanoprokaryote-diatom-green algae in the more polluted station below the crossing with the Highway 4, and to the chrysophytic epiphytes at the mouth. Thus, our study of algal communities in the Alexander River reveals the natural trend of algal diversity and the influence of pollution over the river. On the basis of bioindication methods the Alexander River is characterized as moderately transformed, with changes of algal communities revealing hot spots of anthropogenic impactmineralized, low streaming, and alkaline with a moderate level of organic pollution. We conclude that the EU Framework indication system is applicable for the assessment and monitoring of aquatic ecosystems in Israel related to rehabilitation program for the river.