Structure and Dynamics of Rotifer Community in a Lotic Ecosystem

Abstract

The Vishwamitri is one of the major rivers of central Gujarat and on its banks evolved the picturesque city of Vadodara. Like any other lotic ecosystem of the modern era, the Vishwamitri too is used as a dumping ground for domestic and industrial wastes. Nevertheless, the river inhabits a sizable population of microfauna and the notable among them is rotifer. The current study was aimed at understanding the factors influencing the structure and dynamics of rotifer community in the river Vishwamitri. Seasonal sampling was done during 2002–2004 from five selected sampling stations that were representing upstream, midstream, and downstream of Vishwamitri. These stations, therefore, varied in their pollution loads. The taxonomic analysis of rotifers revealed the presence of 59 species, belonging to 24 genera and 17 families. The Lecanidae family had the maximum representation with 18 species followed by Brachionidae with 15 species. However, species belonging to Brachionus genus are found as the predominant group, among rotifers, in Vishwamitri. Further, a definite periodicity in the rotifer community was noticed on a temporal scale at all the stations. The species diversity was observed to be highest during the post-monsoon, whereas the least diversity was observed during winter. Analysis for water chemistry followed by suitable statistical analysis revealed that the rotifer community responded differently to various physicochemical cues. Dissolved oxygen, normally a major rate-limiting parameter for aquatic life, was found to have no statistically significant influence in regulating rotifer diversity. The study further revealed that elevated levels of suspended solids and total reactive phosphate have a negative influence on the rotifer diversity. Pearson’s correlation between rotifer diversity and temperature as well as pH revealed that rotifers thrive well in warm alkaline part of the river. In addition nitrate nitrogen and chlorophyll-a levels had a significant positive influence on rotifer community composition. To sum it up in the current study, we observed that water chemistry does influence rotifer community in Vishwamitri River and the prominent among the chemical parameters that influence the rotifer community are pH and chlorophyll-a. The right blend of these abiotic factors together with the presence of aquatic macrophytes makes the upstream sampling stations of Vishwamitri richer in terms of rotifer diversity as compared to their more polluted downstream stations.