Seasonal Variation in Zooplankton Community Structure of Ramgarh Lake, Jaipur, Rajasthan

Ramgarh Lake (Jaipur, Rajasthan) was studied for a period of one year from October 2005 to September 2006 for physico-chemical parameters and zooplankton community structure. Collections were taken on monthly basis and both qualitative and quantitative analysis were made to investigate the abundance and distribution of zooplankton. Biodiversity of zooplankton has been calculated using Shannon-Weaver index. The zooplankton community was composed of 17 species of rotifera, 12 species of copepoda, 10 species of cladocera, 5 species of protozoan, 3 species of ostracoda and 2 species of insecta. Numerically copepoda was dominated for 6 months from December to May with Mesocyclops hyalinus constituting the largest share of copepoda. Cladocera was dominated during July to November while in the month of June, rotifera was the dominant group. The observations further reveal that 2 species of cladocera (Diaphanosoma excisum and Moina dubia) and one species of copepoda (Mesocyclops hyalinus) were reported to be perennial. Correlation between various physico-chemical parameters and zooplankton density was calculated according to Karl Pearson's formula. Some of the changes in zooplankton community structure was found associated with seasonal changes in temperature, BOD, COD and nutrient content of the lake water. A highly significant positive correlation was found between rotifera and nitrate content of water whereas ostracoda showed a positive relationship with both nitrate and phosphate content. Total zooplankton density and cladocera showed a negative relationship with COD and BOD while copepoda showed a negative relationship with COD.