Zooplankton diversity and limnological parameters in river Sal, Goa

Abstract

Water is the key substance for the survival of all living organisms. The quality of water in terms of physicochemical parameters affect the conditions for the existence of zooplankton. India is blessed with thousands of water bodies, both large and small, ranging from pond to large lakes, rivers and streams of lentic or lotic nature. Despite several studies, still a large number of them are virgin and yet to be studied. Hence studies on the diversity and seasonal abundance of zooplankton in river Sal, one of the lesser known rivers of Goa was carried out. Analyses of physicochemical parameters showed the following range: Temperature (24.5-30 degrees C), pH (6.60-8.0), EC (17782-52845), total alkalinity (36.03-1188.33mg/l), DO (3.96-7.10mg/l), turbidity (10.35-34.12NTU), nitrates, (0.07-1.94 mg/l), phosphates (0.01-0.19 mg/l), calcium (15.76-1438 mg/l) and magnesium (1.93-240 mg/l). A total of 30 species belonging to Cladocera (10 sps.), Copepoda (9 sps.), Rotifera (9 sps.) and Ostracoda (2 sps.) were identified. Rotifers showed dominance in number followed by Copepoda, Cladocera and Ostracoda. The percentage of zooplankton population was highest (45 percent) during the pre-monsoon and lowest (22 percent) during the monsoon period. The observations further reveal the presence of Alona quadrangularis only during the monsoon season whereas Mesocyclops hyalinus and Testudinella patina only during the post-monsoon season. Shannon-Wiener Index, Simpsons diversity index, Margalef's richness index and equitability were calculated for zooplankton diversity in this river. No vast variation was observed in the Shannon diversity index (H). Taxa richness was the least in the monsoon season while pre-monsoon season accounted for the highest diversity.