Abstract: Diatom growth strategies, which are used as a proxy to analyze disturbances and environmental impacts, can also provide reliable information about environmental gradients. In this study, we used diatom communities and biological traits to assess the structure of epilithic diatoms after an oil spill in a large tributary of the Iguaçu River (Paraná, Brazil). Epilithon and water samples were taken on July 12th, 2004, and after an unexpected oil spill, on the following days: 09/19, 10/03, and 10/13/2004. We observed that the spill caused a distinct shift in both diatom composition and guild group. Diversity decreased and pollution-tolerant diatoms of the motile group became dominant in response to the elevated nutrient levels and reduced light. Tube-forming diatoms, which are strong competitors for light, dominated the epilithon 24 days after the oil spill. Both diatom guilds and growth forms were successfully used to predict the environmental conditions. While diatom guilds responded to disturbances along a temporal gradient, changes inside the guilds were the main factor for understanding the environmental gradient.

RESUMONitzschia persuadens, originalmente descrita a partir de águas estuarinas da Laguna de Veneza, é uma diatomácea raramente citada na literatura desde a sua proposição e é registrada aqui pela primeira vez em ambiente epicontinental da América do Sul. Características morfológicas desta espécie, tais quais valva levemente panduriforme, com uma ondulação reta longitudinal na face valvar, areolas poroidais e sistema de rafe fortemente excêntrica, claramente atribui esta ao gênero Tryblionella, e a sua transferência foi feita. São apresentadas novas observações sobre a morfologia da frústula e comparações com espécies afins. Análises em microscopia óptica de eletrônica de varredura de Tryblionella persuadens comb. nov. do rio Cachoeira, Nordeste do Brasil, foram documentadas.

ABSTRACTThe species originally described from brackish waters of the Venetian Lagoon asNitzschia persuadens is a diatom rarely cited in the literature since its proposition and it is here recorded for the first time in a freshwater environment in South America. Morphological features of this species, such valve slightly panduriform, with a longitudinal straight fold of the valve face, poroidal areolae, and strongly eccentric raphe system clearly assign this species to Tryblionella, and the transfer was made. Here we present new observations on the frustule morphology and comparisons with related species. Light and scanning electron microscopy data of Tryblionella persuadens comb. nov. from Cachoeira River, Northeastern Brazil are documented.

Este trabalho é uma contribuição ao inventário das diatomáceas dos rios da área a ser inundada para a construção do reservatório da Usina Hidrelétrica de Salto Caxias, localizada no Município de Capitão Leônidas Marques, sudoeste do Estado do Paraná, Brasil. Coletas foram realizadas, mensalmente, de março de 1997 a fevereiro de 1998, em 8 estações de amostragem, abrangendo o Rio Iguaçu e seus afluentes, os rios Cotegipe, Jaracatiá, Chopim, Tormenta, Adelaide e Guarani. Nove táxons infragenéricos pertencentes à família Fragilariaceae foram identificados: Asterionella formosa Hassal var. formosa, Fragilaria capucina var. fragilarioides (Grunow) Ludwig & Flôres, F. capucina var. vaucheriae (Kützing) Lange-Bertalot, F. delicatissima (Wm. Smith) Lange-Bertalot var. delicatissima, F. javanica Hustedt var. javanica, Martyana martyi (Héribaud) Round var. martyi, Pseudostaurosira brevistriata (Grunow) Williams & Round var. brevistriata, Synedra goulardii Brébisson var. goulardii e S. ulna (Nitzsch) Ehrenberg var. ulna. Martyana martyi e Fragilaria delicatissima foram primeiras citações para o Estado do Paraná.

This is a survey of the diatom flora of rivers in the influenced area of Caxias' Power Plant, in the district of Capitão Leônidas Marques, southwest of Paraná State, Brazil. Samples were collected from March 1997 to February 1998, in eight sampling stations in the Iguaçu River and its tributaries: Cotegipe, Jaracatiá, Chopim, Tormenta, Adelaide, and Guarani rivers. Nine taxa belonging to the family Fragilariaceae were identified: Asterionella formosa Hassal var. formosa, Fragilaria capucina var. fragilarioides (Grunow) Ludwig & Flôres, F. capucina var. vaucheriae (Kützing) Lange-Bertalot, F. delicatissima (Wm. Smith) Lange-Bertalot var. delicatissima, F. javanica Hustedt var. javanica, Martyana martyi (Héribaud) Round var. martyi, Pseudostaurosira brevistriata (Grunow) Williams & Round var. brevistriata, Synedra goulardii Brébisson var. goulardii and S. ulna (Nitzsch) Ehrenberg var. ulna. Martyana martyi and Fragilaria delicatissima were reported for the first time for Paraná State.