Within-river variation in growth and survival of juvenile freshwater pearl mussels assessed by in situ exposure methods
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The early post-parasitic phase is considered to be the most vulnerable life stage of the endangered freshwater pearl mussel (Margaritifera margaritifera), yet little is known about the spatial variability in juvenile performance at a river scale. The main aim of this study was to determine within-river variation in habitat suitability for juvenile M. margaritifera. The growth and survival rates of juveniles (one and two year old) were measured in the Vltava River (Czech Republic) in relation to several physical and chemical variables using a total of 166 bioindication units (individual mesh cages and sandy boxes) during two thermally different vegetation seasons. Three spatial scales were studied: a longitudinal river profile, bottom habitat types, and hyporheic microhabitats. Both the survival rate and growth of the exposed juveniles varied considerably within the studied river. The effect of the longitudinal river profile and the roles of temperature, oxygenation within microhabitats, episodic pollution, and exposure method were demonstrated. This study represents the first example of a hierarchized approach to the assessment of a riverine mussel biotope with the use of bioindication methods. The results demonstrate the importance of the scale and bioindication method used in understanding the suitability of a river environment to juvenile freshwater mussels.
KeywordsLongitudinal profile Margaritifera margaritifera Substrate types Bioindications Conservation Hyporheal
M.Č., O.P.S, and M.B. were supported by grants from the Czech University of Life Science (Internal Grant Agency of Faculty of Environmental Sciences, CULS Prague (20164236)). Support for K.D. came from the Czech Science Foundation (13-05872S) and O.P.S from Technological Agency of the Czech Republic (TB050MZP006). Data on the bioindication and present occurrence of pearl mussels were collected during the implementation of the Czech Action Plan for Freshwater Pearl Mussels managed by the Nature Conservation Agency of the Czech Republic, which is funded by the government of the Czech Republic and is available at www.zachranneprogramy.cz. The administrations of the National Park and Protected Landscape Area granted their permission to work in the area. We would also like to thank Jan Švanyga, Eva Zelenková, Josef Mayer, Veronika Hodaňová, Lenka Myslivečková, Kateřina Rambousková, Simona Němčíková, Kamila Tichá, and Vojtěch Mrázek for their support in the field work.
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