Hydro-climatic consequences on zooplankton diversity and abundance in perennial Vavuniya reservoir and seasonal Thandikulam reservoir in Vavuniya, Sri Lanka

Abstract

Abstract Background Zooplankton exhibit strong responses for minute changes in their habitat. Therefore, this study intended to investigate the impacts of hydro-climatic factors and related water quality variables on zooplankton abundance and diversity in the perennial Vavuniya reservoir (VR) and seasonal Thandikulam reservoir (TR), Vavuniya, Sri Lanka. Results Zooplankton diversity and abundance showed some peculiarities between seasonal and perennial reservoirs under varying hydro-climatic factors and water quality parameters during wet and dry seasons (July 2018–February 2019). There were 14 Rotifera, 4 Cladocera and 5 Copepod species in VR, and in TR, 12 Rotifera, 2 Cladocera and 5 Copepod species were identified. Although these reservoirs are located at proximity (2.48 km), the responses via zooplankton community structure toward environmental factors have been shown uniqueness to some extent. Significant negative correlation was observed for increasing $${\text{NO}}_{{3}}^{ - }$$ NO 3 -  (p = 0.044) and $${\text{PO}}_{{4}}^{{{3} - }}$$ PO 4 3 -  (p = 0.010) concentrations with zooplankton diversity in perennial VR; however, only $${\text{PO}}_{{4}}^{{{3} - }}$$ PO 4 3 - concentration showed a significantly (p = 0.042) negative correlation in seasonal TR. Interestingly, total zooplankton abundance showed significant negative correlations with $${\text{NO}}_{{3}}^{ - }$$ NO 3 - (p = 0.013) and $${\text{PO}}_{{4}}^{3 - }$$ PO 4 3 - (p = 0.038) in perennial VR; however, insignificant negative correlation was observed in seasonal TR. Copepods make up the majority of total zooplankton abundance in both reservoirs and were significantly affected by increased atmospheric temperature. Cladocera abundance in VR was highly sensitive (p = 0.032; r = − 0.856) to changes in water level. Increasing water level significantly favors the total zooplankton abundance in the seasonal reservoir but not in perennial. Conclusions Sensitivity of zooplankton community structure varies between seasonal and perennial reservoirs in different magnitudes. This is due to the increasing temperatures, increasing phosphate levels and decreasing water levels with the combination of other factors resulting in specific responses of zooplankton diversity and abundance. Therefore, it would not be surprised to use zooplankton community structure to sense the vibrant responses of different freshwater habitats.