Habitat factors differentiating the occurrence of Ostracoda (Crustacea) in the floodplain of a small lowland River Krpiel (N-W Poland)

We analysed the occurrence of ostracods in a small river, taking into account all the types of water bodies in the floodplain - these included helocrenes, oxbow lakes, and ponds, as well as the main river channel. The objective of the study was to investigate the variation in ostracod communities and identify those factors determining species distribution. The environmental factors considered were the type of water body, responsible for 17% of the variance, the physical and chemical water properties (29%), and the biotic and abiotic factors associated with the substrate type (23%). Among the factors associated with the substrate, sediment sorting, plant coverage and insolation were the most important. The ostracod fauna of the helocrenes differed from that of the other water bodies in the floodplain. In the water bodies of the Krpiel valley and in the main river channel, 33 ostracod species were recorded, of which 26 were found in the main river channel. Refugia in the floodplain were the main source of the diversity and abundance of ostracods in the main river channel. The mean density in the main river channel was very low, at 330 indiv. m(-2), while in the water bodies of the floodplain it was the greatest, reaching up to 5568 indiv. m(-2). Nous avons analyse la presence des ostracodes dans une petite riviere, en tenant compte de tous les types de plans d'eau dans la plaine d'inondation; ceux-ci comprenaient des sources helocrenes, des bras morts et des etangs, ainsi que le chenal principal de la riviere. L'objectif de l'etude etait d'etudier la variation des communautes d'ostracodes et d'identifier les facteurs determinant la distribution des especes. Les facteurs environnementaux consideres etaient le type de masse d'eau, responsable de 17% de la variance, les proprietes physiques et chimiques de l'eau (29%), et les facteurs biotiques et abiotiques associes au type de substrat (23%). Parmi les facteurs associes au substrat, le tri des sediments, la couverture vegetale et l'ensoleillement etaient les plus importants. La faune ostracodienne des sources helocrenes differait de celle des autres masses d'eau de la plaine d'inondation. Dans les masses d'eau de la vallee de la Krpiel et dans le chenal principal de la riviere, 33 especes d'ostracodes ont ete enregistrees, dont 26 dans le chenal principal de la riviere. Les refuges dans la plaine d'inondation etaient la principale source de la diversite et de l'abondance des ostracodes dans le canal fluvial principal. La densite moyenne dans le canal fluvial principal etait tres faible, 330 indiv. m(-2), tandis que dans les masses d'eau de la plaine d'inondation, elle etait la plus elevee, atteignant jusqu'a 5568 indiv. m(-2).