Colacium vesiculosum Ehrenberg (Euglenophyceae) es un epibionte común en microcrustáceos del plancton de aguas continentales. La interacción epibiontes y organismo substrato es poco conocida, particularmente en ambientes subtropicales de América del Sur. Se analiza la prevalencia, densidad, biomasa y sitios de adhesión de C. vesiculosum en microcrustáceos planctónicos de un lago subtropical de Argentina. Con el fin de evaluar si los epibiontes afectan la tasa de filtración de Notodiaptomus spiniger Brian, crustáceo dominante del zooplancton, se realizaron bioensayos utilizando el fitoplancton <53µm. Los crustáceos fueron muestreados con un tubo de PVC (1m de largo, 10cm de diámetro) filtrándose 50L de agua a través de una red de 53µm de abertura de malla. El recuento de los microcrustáceos se realizó en cámaras de Bogorov bajo microscopio estereoscópico. Los organismos infectados fueron separados y observados al microscopio fotónico para determinaciones de densidad y biovolumen de los epibiontes, y su distribución en el exoesqueleto. La prevalencia de C. vesiculosum fue mayor en crustáceos adultos que en estadíos larvales y juveniles. El grupo más infestado fue el de los copépodos calanoideos en relación con su alta densidad. Los sitios de adhesión sobre el exoesqueleto fueron las regiones del cuerpo que durante la locomoción y alimentación tienen mayor probabilidad de encuentro con los epibiontes: antenas y patas toráxicas en copépodos, patas toráxicas y postabdomen en cladóceros. Valores similares en la tasa de filtración entre individuos infestados y no infestados de N. spiniger y la constante prevalencia (<40%) del alga epibionte sugieren que C. vesiculosum no condicionaría la vida de los microcrustáceos planctónicos del lago Paiva.

Colacium vesiculosum (Euglenophyceae) is an epibiont common on planktonic microcrustaceans of continental waters. The interaction between epibionts and substrate organisms is not very well known, particularly in subtropical environments of South America. In the present work, we analyzed the prevalence, density, biomass and attachment sites of C. vesiculosum on planktonic microcrustaceans from Paiva Lake, a subtropical lake of Argentina. With the aim to evaluate whether epibionts affect the filtering rates of Notodiaptomus spiniger, the dominant planktonic crustacean, we carried out bioassays using phytoplankton <53µm. Crustaceans were sampled using a PVC tube (1.2m long and 10cm in diameter), filtering 50L of water through a 53µm-mesh. Microcrustaceans were counted in Bogorov chambers under a stereoscopic microscope. The infested organisms were separated and observed with a photonic microscope to determine density and biovolume of epibionts, by analyzing their distribution on the exoskeleton. The prevalence of C. vesiculosum was higher in adult crustaceans than in their larvae and juveniles. The most infested group was that of calanoid copepods, related to their high density. The attachment sites on the exoskeleton were found to be the portions of the body which have a higher probability of encounter with epibionts during locomotion and feeding, i.e., antennae and thoracic legs in copepods, and thoracic legs and postabdomen in cladocerans. The similar values found in the filtering rate of infested and uninfested individuals of N. spiniger and the constant prevalence (<40%) of epibiont algae, suggest that C. vesiculosum does not condition the life of planktonic crustaceans of Paiva Lake. Rev. Biol. Trop. 59 (3): 1295-1306. Epub 2011 September 01.

No presente trabalho foram estudadas as mudanças na densidade e na diversidade de zooplâncton dos rios Salado e Negro no período de março de 1993 a outubro de 1994. As amostragems quantitativas de zooplâncton foram realizadas com uma bomba de sucção usando uma rede de 53 µm de abertura de poro. Densidades muito altas foram encontradas na cabeceira do rio Salado. A densidade média nos rios Negro e Salado foi variável na fase de enchente. As mudanças na abundância do zooplâncton estiveram relacionadas com as varíaveis hidrológicas, mudanças na condutividade e as estações do ano. A densidade do zooplâncton foi correlacionada positivamente com a temperatura, transparência da água e flutuações da densidade do fitoplâncton. Em ambos os rios, os rotíferos foram o grupo dominante do zooplâncton. No período de enchente, as espécies abundantes foram limnoplanctônicas e algumas ticoplanctônicas. Na vazante dominaram as espécies eurihalinas e limnoplanctônicas. No rio Negro, com uma maior planície de inundação, registrou-se a máxima diversidade e riqueza específica. Não se encontrou similaridade na composição específica entre os rios Salado e Negro.

Zooplankton abundance and diversity of Salado and Negro rivers were compared in relation to the water level fluctuations. The zooplankton pumper samples were collected between March, 1993 and October, 1994. Mean zooplankton density at Salado river was very higher in upstreem. Zooplankton density in the Negro and Salado rivers were variable in the high water phase. Changes in the density appeared to be related to the hydrologic phases, seasonal cycle and conductivity variation. The zooplankton abundance was positively correlated with the abiotic and biotic factors (temperature, transparency and fitoplankton). The dominant group in the two studied rivers were the rotifers. The dominant species in the high water phase were limnoplanktonic and scarce ticoplanktonic organisms, in the low water phase the present organisms were euryhalin. The highest diversity was taken in the Negro river with major floodplain. The Jaccard Index (1908 ) showed no similarity zooplankton between Salado and Negro rivers.