Spatial processes affect community concordance in a Neotropical reservoir

Background/Question/Methods

The construction of dams results in habitat degradation, with marked effects on the aquatic ecosystems. Abiotic factors, as integrity of riparian vegetation, spatial differences in habitat diversity, structural complexity, physical and chemical variables, morphometric characteristics, and biotic interactions affect the distribution of species in reservoirs and in surrounding lateral lagoons. Notwithstanding, little knowledge has been produced correlating several Neotropical aquatic communities and environment features in reservoirs with different kinds of lateral lagoons. Based on this, the aim of this study was to examine the effect of the spatial scale on the strength of community concordance among phytoplankton, zooplankton, macroinvertebrates, and fish assemblages by comparing the concordance between ordinations of these groups in Rosana Reservoir (Paranapanema River, Brazil). Six surveys from September 2004 to August 2005 were carried out in four lateral lagoons and in one sampling site in the main river channel. One lagoon was originated by the flood of mining digging; two were natural, and the last one was built to serve as watering to animals and agriculture. Matrices of spatial and environmental variables were summarized using a Canonical Correspondence Analysis (CCA) to examine the relationship between environmental features and community structure. Multivariate summaries were tested using a Procrustean superimposition approach (ProTest).

Results/Conclusions

CCA results showed spatial and environmental variables that emerged as the best correlates of the biotic patterns were temperature for phytoplankton, total nitrogen for zooplankton and dissolved oxygen for macroinvertebrates and fish. Transparency, dissolved oxygen and total nitrogen appeared as the strong environmental correlates for all groups. In this analysis, a spatial segregation between the lateral lagoons and reservoirs was registered in all biologic groups. ProTest analysis revealed better correlation between macroinvertebrate vs. zooplankton and macroinvertebrate vs. fish than the primary groups (phytoplankton vs. zooplankton). Averaged standardized sample residuals from the ProTest comparisons among the taxonomic groups in the complete data set revealed a distinct ‘‘concordance gradient’’ among sites. However, transparency, dissolved oxygen, and total nitrogen were significantly correlated with sample residuals, indicating that concordance among the groups tended to increase in the lateral lagoons. Results suggest that local processes, as limnological and structural characteristics of habitat, and intra- and interspecific interactions, are the main structuring factors on aquatic communities in reservoirs and its different kinds of lateral lagoons. Hence, conservation measures are essential to maintain the environmental integrity of development areas (lateral lagoons) for the maintenance of biodiversity in the Rosana reservoir.