Inventaire des Odonates et Biosurveillance des deux sous bassins versants (Oued Medjrda et Seybouse) dans la région de Souk Ahras (Nord-Est algérien)

Abstract

In the context of global biodiversity collapse, achieving a balance between the development of agricultural and industrial activities -sources of wealth- and the preservation of natural ecosystems represents a major challenge. However, conservation efforts become more complex when available knowledge about species communities within these ecosystems is insufficient to accurately assess the magnitude of impacts or to develop effective strategies aimed at mitigating and limiting their effects. This thesis aims to present Odonata as model species, by analyzing their diversity, distribution, and the environmental factors influencing their presence in two sub-watersheds: Medjerda and Cheref, located in Souk Ahras, northeastern Algeria. Twenty-seven taxa were inventoried across both sub-watersheds, including 20 species recorded in Medjerda and 22 in Cheref. The composition of species assemblages specific to each sub-watershed is mainly governed by climatic factors, the abundance of riparian vegetation, habitat openness, and hydroperiod. Despite the clearly visible human footprint in these hydrosystems, the diversity of species they harbor, including Coenagrioncaerulescens and Trithemiskirbyi, recently reported as new to Numidia and confirmed by our observations, as well as the abundant presence of Coenagrionmercuriale (in Medjerda), a locally threatened species, highlight their essential role for Odonatological biodiversity at the regional scale. Moreover, the analysis of parasitic infestation observed in the studied species reveals a notable presence of aquatic mites in four Zygoptera species, with a marked preference for Platycnemissubdilatata. These results raise several questions regarding this parasitic preference, calling for further research to better understand the mechanisms of interaction between Odonata and their ectoparasites, as well as the coevolutionary dynamics involved. Water quality analysis, conducted at three selected stations in Medjerda, revealed significant variations in certain physicochemical parameters. By linking these parameters to the distribution of Odonata larvae, we observed a marked impact on community structuring. Factors such as conductivity, stream width, and resistivity appear to play a key role in species distribution, highlighting their sensitivity to environmental fluctuations and their value as bioindicators of aquatic ecosystem quality.