Ecology, abundance and richness of zooplankton in Chandubi Wetland, Assam, Northeast India

Zooplankton, being the primary consumers in an aquatic ecosystem, convert plant proteins into animal proteins and play a significant role in nutrient cycling. Northeast India is endowed with numerous wetlands but limnological evaluation of most of these wetlands remains unattended or leaves gaps and information on zooplankton diversity is insufficient. The present study aimed to assess the zooplankton diversity and temporal variation in their richness and abundance in relation to the physico-chemical attributes of Chandubi wetland for period of one year in 2021. The investigation revealed the occurrence of 79 species belonging to 7 groups: Protozoa (20 species), Gastrotricha (2 species), Rotifera (32 species), Copepoda (8 species), Cladocera (15 species), Conchostraca (1 species), and Ostracoda (1 species). The abundance of these groups was ranked as: Rotifera (67.3%) > Cladocera (14.6%) > Copepoda (9.2%) > Protozoa (8.2%) > Conchostraca and Ostracoda (> 1%). The trend of zooplankton richness in different seasons was- monsoon > retreated monsoon > pre-monsoon > winter, while their abundance was- pre-monsoon > winter > retreated monsoon > monsoon. Zooplankton density showed a significant (p<0.05) positive correlation with pH, Dissolved oxygen and Secchi disk transparency while it showed a negative correlation with temperature and free carbon dioxide. CCA plot revealed the abundance of Protozoa in the sampled wetland was influenced by calcium, total hardness and water temperature, while that of Rotifera by phosphate, Copepoda by total hardness and calcium, and Cladocera by nitrate content of the water. High dominance of rotifers indicated the prevalence of eutrophic conditions in the wetland.