Hidrológiai Közlöny, 2017 (97. évfolyam)
2017 / 3. szám - TRANSNATIONAL EFFORTS - Sandu, Cristina - Dumitrache, Alina - Radu, Emilia - Dobre, Doru - Tudorache, Mädälina - Mihăilescu, Simona: The importance of good ecological status for the successful revival of Danube sturgeon
Hidrológiai Közlöny (Hungarian Journal of Hydrology) 2017. 97. évf. 3. sz. on the Danube biodiversity, in particular on species and habitats protected by the European environmental legislation and international conventions ratified by riparian countries. BIOLOGICAL COMMUNITIES Aquatic ecosystems are inhabited by myriads of organisms fully dependent on the quality of their habitats. They ensure the functioning of the ecosystem and provide various services such as oxygen production, biogeochem- ical cycling of nutrients, decomposition of organic waste, water purification, provisioning of drinking water and food, etc. These organisms are grouped in three major classes (producers, consumers, decomposers), each category with distinct roles in the aquatic ecosystems, strongly interlinked with each other. In the presence of light, the primary producers (planktonic and periphytic algae, macrophytes) synthesize organic matter through photosynthesis, rendering it available for the higher trophic levels. The primary consumers (zooplankton, benthic macro-invertebrates, fish juveniles and planktivorous fish) ingest the organic matter created by the producers, becoming in turn food resource for secondary or tertiary consumers (small fish, larger fish, aquatic birds). In aquatic ecosystems, large predatory fish (pike, catfish, sturgeon) or waterfowl feeding on fish (pelicans, cormorants, white-tailed eagles) are the highest ranked consumers and therefore, they are good ecological indicators of ecosystem health. The microbial communities play an essential role in recycling organic matter as they decompose the excreta of aquatic organisms, the detritus and the decaying bodies, preventing their accumulation in the aquatic systems and mineralizing the nutrients, to be used again by primary producers in a new cycle. Freshwater ecosystems, such as rivers, lakes and wetlands are particularly important for biodiversity conservation, as although they only represent 0.01% of the world’s water resources, they host almost 10% of known species (Balian et al. 2008). As many human activities rely on freshwater resources, these water bodies are highly impacted by industrial and agricultural pollution, hy- dromorphological alterations, land use change, overexploitation, invasive alien species and climate change. Consequently, the species living in freshwater habitats have undergone the most dramatic decline among all groups of species: 81% between 1970 - 2012 (figures based on data from 3,324 monitored populations of 881 freshwater species) (WWF 2016). At European level, a seven-year assessment has shown that 200 out of 522 of Europe’s freshwater fish species are at risk of extinction, 12 already being extinct (Kottelat and Freyhof2007). The Danube River Basin still hosts rich biodiversity and a high number of species and habitats of community interest, especially in its middle and lower stretches. Numerous critically endangered fish species are sheltered here, such as sturgeon, European eel and pontic shad, being protected by several EU directives and international conventions and included in the Natura 2000 network. However, the pressures exerted on the aquatic habitats, especially overfishing and the hydrotechnical constructions obstructing their spawning migration have led to a dramatic decline of long-distance migratory species. This is particularly true for the Danube sturgeon, considered the flagship species of the Danube River Basin (ICPDR 2016). After the construction of the Iron Gates dams in the 1970s and the consequent loss of spawning habitats located upstream the dams, they suffered a sharp decline, being nowadays in a very critical situation: according to IUCN (2010), one species is already extinct (Acipensersturio), four species are critically endangered (Acipensergueldenstaedti, Acipensernudiventris, Acipenserstellatus, Husohuso), and one is vulnerable (Acipenserruthenus). As part of the Biological Quality Elements, sturgeons should be monitored under the WFD. On the other hand, sturgeons are listed in the Annexes II and V of the Habitats Directive (HD 92/43/EEC), and hence, the monitoring of their conservation status is an obligation arising from Article 11 of the HD. The results of the national assessments of the conservation status of species and habitats of Community interest in the EU member states are summarised and reported under Art. 17 of HD to the EU Commission every six years. The year 2013 marked the third reporting date since the adoption of the HD, and the first time when Lower Danube countries such as Romania and Bulgaria, where wild populations of anadro- mous sturgeons still occur, reported the progress made with the implementation of the HD. In Romania, for instance, the sturgeon conservation status was assessed as “unfavourable - bad” (U2) in all the biogeographic regions where these species are distributed (Mihäilescu et al. 2015), indicating that urgent measures are needed at national level. The national conservation measures should be harmonized with the Sturgeon 2020 Programme and strategy to secure sturgeon revival in the Danube River Basin and the adjacent Black Sea (Sandu el al. 2013). Intense cooperation and the commitment of relevant stakeholders in the Danube and Black Sea areas are required in the long term to achieve a “Favourable Conservation Status” of these critically endangered species. ADDITIONAL CHALLENGES FOR ACHIEVING GOOD ECOLOGICAL STATUS Water quality and hydromorphology are key drivers controlling the status of the aquatic communities and therefore, they are pre-requisite conditions for achieving the “good status” of the aquatic ecosystems. However, habitat quality and the diversity of the biological communities are subject to additional challenges that may affect the ecological status, the most important of them being the increasing impact of climate change and the occurrence of Invasive Alien Species (IAS). Climate change Worldwide, the impact of climate change has become ever more obvious during the past decades: air and water temperatures are increasing, glaciers are melting at an unprecedented rate, the precipitation regime has changed
