Oligochaete Community Structure in Paddy fields and Channels in Kole paddy fields, Vembanad Kole wetland, India.

Abstract

Benthic invertebrates including oligochaetes are important components of paddy field fertility due to its significant role in organic matter decomposition and nutrient translocation, but have been studied less. The oligochaete community structure in paddy fields and channels/agricultural ditches of Kole wetlands (a part of Vemband Kole wetlands, a Ramsar site on the south west coast of India) was studied during Punja (summer crop season- January to May 2011). The benthic fauna belonged to the phyla Mollusca, Annelida and Arthropoda. Fifteen oligochaete species of family Naididae, Tubificidae and Lumbriculidae were identified. Seven taxa; Aulodrilus pluriseta, Aulodrilus sp., Aulodrilus piguiti, Branchiodrilus semperi, Stephensonia trivandriana, Pristinella minuta and Pristinella jenkinae were present both in the paddy fields and channels. Six species; Allonais gwaliorensis , Allonais paraguensis, Dero zeylanica, Pristinella accuminata, Pristina menoni, Lumbriculus variegates were exclusively found in the channels and two taxa; Branchiodrilus hortensis, Homochaeta sp. exclusively in the paddy fields. ANOSIM results revealed a similarity in oligochaete composition among paddy fields and channels (Global R=0.19, p>0.05); the lack of environmental specialization in aquatic oligochaetes could be a reason for this. Abundance significantly varied among them, a lower abundance observed in paddy fields (102±161 ind/m 2 ) than channels (891±1409 ind/m 2 ) (ANOVA F 1, 24 =6.02, p<0.05). Less habitable area in paddy field due to the compartmented substratum by paddy root structures resulted in a reduced abundance in paddy fields. Species richness and diversity showed no significant variation but evenness showed a significant variation between paddy fields and channels (ANOVA F 1, 8 =10.40, p<0.05). As oligochaetes are characterized by less dispersal and migration ability evenness component would have been more sensitive than other diversity indices.