Seasonal variation and interrelationship of phytoplankton and Vibrio Cholerae in Bangladesh

Abstract

A total of 17 water variables were studied of the two distinct different geographical areas in Bangladesh for two years (October 2010-September 2012). Out of the two study sites, Mathbaria represents estuarine cholera epidemic pattern whereas Chhatak represents inland epidemic pattern for Vibrio cholerae. In Mathbaria there are four infested stations among eight stations and in Chhatak site there are two infested stations among seven stations. After analyzing the studied variables, it is observed that in Mathbaria site Vibrio cholerae showed a single peak during summer in the month of March through May. Whereas in Chhatak sites cholera peak showed a single peak during autumn in the month of early November i.e. just after the monsoon which contain warm, humid temperature. Stations of Mathbaria showed high level of total dissolved solids (TDS) and salinity while the stations of Chhatak showed higher range in the concentration of soluble reactive phosphorus (SRP), soluble reactive silicate (SRS), nitrate nitrogen (NN), chlorophyll a, phaeopigment (PP), phytoplankton and zooplankton densities. Higher ranges of SRP and NO 3 -N were found in the infested stations of both the study sites. Maximum cell density of Vibrio cholerae at Mathbaria was nearly 500-fold more than Chhatak site. Dominant Phytoplankton in the infested stations of both the study sites belonged to euglenoid and diatoms. During cholera peak of Mathbaria, peak of water temperature, alkalinity, salinity, pH, total dissolved solids (TDS) and phaeopigment also showed the same peak during summer. On the other hand, infested stations of Chhatak showed peak of soluble reactive phosphorus (SRP), nitrate nitrogen (NN) and phaeopigment during autumn season when Vibrio cholerae also showed peak. Pearsons correlation (SPSS v11.5) analysis among the studied variables reveals a significant negative correlation between phytoplankton density and water temperature. In this analysis on one hand significant positive correlation was observed between the phytoplankton and total zooplankton densities. On the other hand, a significant positive correlation between the concentration of phaeopigment and V. cholerae in Mathbaria Station 2, 7 and 10 and in the Station 2 of Chhatak was observed. Phaeopigment (phaeophytin a, cholorophyllide a and two unidentified pigments) is a degraded product of chl a, dominant pigment of phytoplankton. In the analysis, significant positive correlation was also observed between phytoplankton density and total zooplankton. Grazing by copepod (zooplankton) is the major reason for the degradation of chlorophyll a to phaeopigment. So, it can be said that, phytoplankton enhances the growth of zooplankton since peak growth of both phyto- and zooplankton is nearly overlapping or occurs side by side. After the peaks achieved, the plankton population start declining during which a lot of phaeopigment is released in the habitat. Under this enriched conditions of phaeopigment in the habitat, peaks of V. cholerae are mostly observed. To support the strong relationships among the studied environmental and biological variables and sampling periods RDA (Canoco v4.54) is also applied. Results by this multivariate program also support the similar relationship.