Composition and Distribution of Zooplankton in the Pasak Jolasid Reservoir,Lop Buri Province

Abstract

Composition and distribution of zooplankton in the Pasak Jolasid reservoir were studied during 2002. Samples were horizontally, obliquely and vertically drawn at two-month intervals using three mesh sizes plankton nets (22, 40 and 100 μm). A total of 119 species of zooplankton was recorded. Rotifera was the most diverse zooplankton group in this reservoir. The taxa found in decreasing order were as follow : Phylum Rotifera (24 genera, 76 species and 4 varieties), Phylum Protozoa (13 genera and 22 species), Phylum Arthropoda (12 genera, 20 species and 1 group), and Phylum Cnidaria (1 genus, 1 species). An occurrence of the freshwater jellyfish (Craspedacusta sinensis) was the first record in the reservoir of Thailand. Spatial and temporal variations in species number of zooplankton were relatively small ; variation in number of species ranging between 44 and 89. High numbers were recorded in October at one station along Pasak river ranging between 70 and 89 species, while low number ranging between 44 - 54 were recorded in April at two stations located on the bank of the reservoir.