Comparative study on macrobenthic community structure with special reference to oligochaetes during drought and flooded phases in a Tropical Kole wetland, India.

Abstract

Wetlands experience dynamic hydrofluxes which is a major determinant of biotic community structure. Benthic organisms form an integral part of aquatic environment and constitute an important link in the food web. The habitat loss and fragmentation caused by hydrological alterations in wetlands can affect the benthic fauna. This study analyzed the benthic community especially oligochaete species in a wetland during two different phases. Maranchery Kole wetland, a part of Vembanad Kole wetlands (Ramsar site) behaved as two systems within a short span of one year; as flooded phase when the system was a pure aquatic body and drought phase where the system was dry resembling a grass land with isolated water patches. Macrobenthic abundance in flooded and drought phases were (355±122 ind./m 2 ) and (166±60 ind./m 2 ) respectively. The decrease in habitable area along with its consequential effects resulted in a reduced numerical abundance of macrobenthos in the drought phase. Oligochaete abundance was significantly higher in flooded phase (ANOVA F 1, 53 =5.11, p 0.05). Species richness (Margalef’s index) and species diversity (Shannon Wiener index) was higher in drought phase or disturbed phase than flooded phase or undisturbed phase reflecting a glimpse of intermediate disturbance theory. No significant correlation emerged between the environmental variables and benthic abundance implying that the relationship with the measured environmental variables might be weaker or overridden by other unmeasured variables. Further the generalized environmental requirements in aquatic oligochaetes and chironomid larvae, the most abundant taxa in the wetland could be the reason for the lack of correlation.