Hydrobiological variables as a regulatory factor on the abundance of heterotrophic flagellates in an urban pond

The seasonal abundance of flagellates has been monitored over a period of 1 year from December 2013 to November 2014 (divided into 4 conjugative seasons namely winter, spring, summer, and autumn) in an experimental pond located in Rajshahi City Corporation area, Bangladesh. To our knowledge, this study is the first to shed light on the occurrence and possible interrelationships among heterotrophic flagellates (HF), bacteria and zooplankton in Bangladesh and the result obtained by this study will be beneficial for similar water ecosystem all over the world. Standard methods were used to determine the prescribed hydrological parameters and zooplankton cell density. Maximum HF abundance (14 346.00 cells/mL) was found in the spring and the minimum (5 215.00 cells/mL) occurred in the summer. Inverse to HF, significantly (P&;lt;0.05) higher zooplankton abundance was found during the winter (782.00±47.62 cells/mL) and the lowest value was found in the autumn (448.00±39.15 cells/mL). Whereas similar to the HF, total bacterial abundance was significantly higher during the spring ((2.25±1.05)×10⁵ cells/mL) and lower in the summer ((0.79±0.06)×10⁵ cells/mL). Multivariate analyses (ANOSIM and MDS) have shown significant seasonal differences for cell numbers where MDS ordination plot and cluster analysis based on similarity in the genera abundance of HF revealed overlapping condition between winter and spring. Canonical correspondence analysis (CCA) also showed a distinct separation among the genera based on the prevailing hydrological situation and indicated that temperature, pH, BOD₅, and NO ^?₃ were the most important environmental variables in determining the observed variation in HF community structure. Among the biological factors, zooplankton showed negative but total bacteria were positively correlated with HF abundance.