The Odonata (Insecta) assemblage on Eichhornia azurea (Sw.) Kunth (Pontederiaceae)
stands in Camargo Lake, a lateral lake on the Paranapanema River
(state of São Paulo, Brazil), after an extreme inundation episode
FULAN1, J.A. & HENRY1, R.
1 Department of Zoology, Institute of Biosciences, State University of São Paulo, Campus of Botucatu, 18618-000 Botucatu, SP, Brazil.
ABSTRACT: A one-year study examined the variation in abundance and richness of Odonata (Insecta) genera on Eichhornia azurea (Sw.) Kunth (Pontederiaceae) stands in Camargo Lake, a lateral lake on the mouth zone of the Paranapanema River entering Jurumirim Reservoir, São Paulo, Brazil, after an extraordinary inundation episode. Also were investigated the abiotic factors correlating with Odonata presence: water transparency, surface temperature, dissolved oxygen, pH, conductivity, and suspended matter. No significant correlation was found between Acanthagrion Selys, 1876, Coryphaeschna Williamson, 1903 and Oxyagrion Selys, 1876 abundance and abiotic factors. However, Spearman analysis showed a positive correlation between Cyanallagma Kennedy, 1920, Diastatops Rambur, 1842, Enallagma Charpentier, 1840, and Micrathyria Kirby, 1889 larvae densities and suspended matter, and between Homeoura Kennedy, 1920 and Telebasis Selys, 1875 and dissolved oxygen, and a negative correlation between Enallagma, Ischnura Charpentier, 1840, and Micrathyria and transparency. The highest absolute abundances were recorded in March, August, September, and October 2004, and March 2005. Comparing genera richness, absolute density, dissolved oxygen, total E. azurea biomass, and suspended matter with data from a period prior to the perturbation, there was reduced Odonata abundance, E. azurea biomass, suspended matter, and dissolved oxygen after the inundation episode, while genera richness increased. The decrease in macrophyte biomass and suspended matter after the inundation episode promoted a reduction in larvae shelter sites and in food resource, and thus on Odonata abundance. The low post-inundation levels of oxygen in water did not affect Odonata abundance, probably due to morphological and physiological adaptations in larvae for survival under low oxygen conditions. When Coryphaeschna larvae (the longest Odonata sampled) were collected, low genera richness was recorded. Odonata presence limited to Coryphaeschna larvae probably reduced food resources for the other genera.
Key-words: Odonata, larvae, abundance, richness, lake, inundation.