Chironomidae (Diptera) community structure in two subsystems with different states of conservation in a floodplain of southern Brazil

AIM: Our study aimed to compare the composition, distribution, diversity, abundance and dominance of Chironomidae in two subsystems of the Upper Paraná River floodplain, with different levels of conservation. We expected to find the highest values of diversity and lowest dominance of taxa in the most conserved areas (Ivinhema subsystem). We also expected to detect differences in the composition and distribution of communities between the subsystems, because of the level of conservation of each subsystem; METHODS: Sampling was performed in March and September 2003, in eight stations, four in the Paraná River subsystem and four in the Ivinhema River subsystem. Four samples were taken at each point with a modified Petersen-type sampler: three for biological analysis and one for sedimentological analysis. Chironomidae larvae were identified to generic level; RESULTS: Twenty-nine genera belonging to three subfamilies (Tanypodinae, Chironominae and Orthocladiinae) were recorded in this study. Chironomus, Dicrotendipes, Goeldichironomus, and Tanypus were the main genera found in the Paraná subsystem. Polypedilum was the only genus present in all sampling stations, and was dominant in five of them. In the Paraná subsystem we observed the highest values of dominance, and in the Ivinhema subsystem the largest number of rare taxa; CONCLUSIONS: Results showed differences in the structure of the Chironomidae community between the Paraná and Ivinhema subsystems. The community of Chironomidae in the Paraná subsystem was composed predominantly by generalist and tolerant genera. In the Ivinhema subsystem we observed higher richness of taxa. The greatest diversity, lowest values of dominance and exclusive taxonomic composition in the Ivinhema River subsystem could be reflecting a less degraded environment, demonstrating that the conservation of these areas is essential for maintaining the diversity of Chironomidae.