Differences in Potamogeton praelongus Morphology and Habitats in Europe

One of the most southern European occurrences of Potamogeton praelongus is in the Czech Republic (CR), with only one native population in the Orlice River floodplain in Eastern Bohemia, the only surviving site from 10 Czech localities known 45 years ago. This species is critically endangered in the CR and needs to be actively protected with a rescue program. The number of P. praelongus sites increases along a latitudinal gradient, from Central to North Europe (CR, Poland, Sweden, and Norway), and correlates with improving conditions (water transparency and nutrient content in water) for this species along this gradient. Although differences in site conditions between Central and North Europe were caused by changes in landscape geomorphology and vegetation during the glacial and postglacial eras, presently, anthropogenic impact is primarily observed. The Czech sites for P. praelongus have distinctly lower water depth and transparency, and conversely, higher conductivity, temperature, and shade levels than the Nordic ones. These extreme conditions in most biotopes of this light-demanding and mesotrophic species in the CR result in lower fitness and different morphological parameters in the Czech populations. These changes lead to decreased competitive ability against filamentous algae and more competitive aquatic plant species and increase the impact of animals. The Nordic nonintensively managed landscape provides numerous large, deep lakes, which are optimal for this aquatic species. In the CR, P. praelongus can currently only survive in rivers and their oxbows, but these are heavily influenced by intensive landscape management and fishing. Comparison of the populations and their site conditions in the CR and other European countries showed that all Czech native and artificially established sites are exposed to eutrophication and its consequences, which are the most important factors affecting the survival of P. praelongus .