Inland swamps in South East Asia harbour hidden cladoceran diversities: species richness and the description of new paludal Chydoridae (Crustacea: Branchiopoda: Cladocera) from Southern Thailand

Abstract

Freshwater surveys in the tropics have high potential for revealing new taxa if a wide range of habitats is included. Tropical inland swamps are ignored during most zooplankton sampling campaigns. We show that swamps harbour underestimated Cladocera diversities in South East (SE) Asia, illustrated here for Southern (S) Thailand. According to our preliminary data, based on 22 swamp sites in ten provinces, the cladoceran diversity of swamp habitats is high (about 73 taxa), i.e. a species richness of about 85% of the cladoceran taxa recorded in S Thailand. The Chydoridae are the most diverse group, about 66% of the total (48 out of 73 species), followed by the Macrothricidae (12%; 9 species) and the Sididae (11%; 8 species). Daphniidae only occupy a small proportion of the total species in these sites (5%; 4 species). Besides rare taxa, the SE Asian tropical swamps contain new records, even new species. We discuss the importance of tropical swamp habitats as hotspots of cladoceran diversity, which are being destroyed through agricultural and urban development in SE Asia. As an example, we describe two new paludal species of the Chydoridae (Crustacea: Branchiopoda: Cladocera), restricted to inland swamps in S Thailand. The new taxa have conspicuous morphologies within their respective genera (Karualona Dumont and Silva-Briano, 2000 and Notoalona Rajapaksa and Fernando, 1987), compared to their common sister species in the region. Karualona serrulata n.sp. is separated from congeners by i) divided denticles on the posteroventral corner of the valves and ii) single setules on the anterior face of the first limb (instead of groups of setules, as in the majority of the Aloninae). We include notes on the other, common Karualona sp. populations from S Thailand. These animals show similarities with K. iberica and K. karua, yet belong to neither; we discuss the variability of characters in these populations and in the genus. The second new taxon, Notoalona pseudomacronyx n.sp., is a small species with a postabdomen strongly resembling that of Alona macronyx Daday, 1898, recently allocated to Celsinotum. It seems closest in morphology to an African, yet undescribed species of Notoalona. We included pictorial keys to all the species of these two chydorid genera, which have their main distribution in the circumtropics.