Species diversity of cladocerans and copepods in the floodplain of the River Mun,Northeast Thailand(Thai)

Abstract

The species diversity of cladocerans and copepods from 70 habitats in the floodplain of the Mun River of Surin, Sri Sa Ket and Roi Et Provinces, Thailand was investigated. One hundred and forty qualitative samples were collected by a 60 µm mesh plankton net during pre-monsoon (April - May 2000 and May 2001) and post-monsoon (October 2000) periods. Sixty-three species from 33 genera of cladocerans were identified, and seven [Kurzia brevilabris Rajapaksa and Fernando, Leydigia cf. australis (Sars), Pseudochydorus globosus (Baird), Simocephalus heilongjiangensis Shi & Shi, Ilyocryptus raridentatus Smirnov, Grimaldina brazzai Richard and Diaphanosoma dubia (Manuilova)] of which are new to Thailand. The number of cladocerans recorded in pre-monsoon and post-monsoon sampling periods was not different significantly (P > 0.05) and most of the taxa recorded are circumtropical species. According to the frequency of occurrence, the most common cladocerans was Bosminopsis deitersi Sars (98.5% of the sampled localities), followed by Ceriodaphnia cornuta Sars (97.9%), Moina micrura Kurz (87.1%), Diaphanosoma volzi Stingenlin (87.1%) and D. excisum Sars (84.3%), respectively. Twenty species of calanoid and 8 of cyclopoid copepods were recorded, and two [Cryptocyclops linjanticus (Kiefer) and Paracyclops affinis (Sars)] of them are new to Thailand. The most frequently encountered species were Mesocyclops thermocyclopoides (Harada) (82.9% of the sampled localities), Neodiaptomus yangtsekiangensis Mashiko (77.1%) and Mongolodiaptomus botulifer (Kiefer) (75.4%). In addition, the species diversity of cladocerans has a non-significantly negative correlation with salinity, while the species diversity of copepods has a significantly positive correlation with conductivity (r = 0.22, p = 0.01), but it has a nonsignificantly negative correlation with dissolved oxygen (r = -0.22, p= 0.84) and pH (r = -0.04, p = 0.68).