Composition and community structure of aquatic invertebrates in an irrigated paddy field ecosystem

Abstract

Random sampling of paddy field water and soil was carried out at fortnightly intervals during five paddy cycles in a paddy field ecosystem at Bathalagoda. The aquatic invertebrate communities examined included neuston, zooplankton, nekton, periphyton and benthos. Zooplankton were extracted from water samples using a plankton net. Neustonic, nektonic and periphytic organisms were collected by using a standard dipper and subsequent sieving. Periphytic and benthic molluscs were studied by quadrate sampling. Benthos were extracted from wet soil core samples.

Hemipteran insects formed the major neustonic group (87%, 4 spp.), followed by collembolans (13%, 2 spp.). The zooplankton were dominated by crustaceans (17 spp.), followed by rotifers (15 spp.). The nektonic and periphytic community were also dominated by adult and larval insects (96%, 45 spp.) while the balance consisted of crustaceans (l spp.), turbellarians (l spp.), hydracarina (03 spp.) and leeches (2 spp.). Majority of the aquatic molluscs were benthic forms (74%, 7 spp.) followed by periphytic forms (26%, 3 spp.). The benthic organisms were dominated by nematodes (74%, 7 spp.), followed by arthropods (9%, insects: 7 spp, crustaceans: 5 spp. ), earthworms (9%, 20 spp.), turbellarians (8%, 8 spp.) and rotifers (1%, 3 spp.). Other aquatic micro-organisms recorded included Protozoa (15 genera), Cnidaria (1 genus) and Gastrotricha (1 genus). Agronomic practices resulted in differential fluctuations of the aquatic invertebrate groups.

Financial assistance by NARESA Grant RG/95/B/4 is acknowledged.