Zoo-heleoplankton structure in three artificial ponds of North-eastern Argentina

The aim of the present study was to compare the abundance and species richness of zoo-heleoplankton bigger than 53 µm in an annual cycle under similar climate conditions in three artificial ponds, in order to observe the changes during an annual cycle. Samples were taken monthly from June 1993 to July 1994 in Corrientes, Argentina. The first pond (A) was covered an 80% by Eichhornia crassipes (Mart.), the second one (B) with bloom of Microcystis aeruginosa (Kurtzing) and the last one (C) with organic matter deposited in the bottom. The water was more acidic at pond A, and the water at pond B contained more dissolved oxygen concentration than the water at the other two ponds. The zoo-heleoplankton densities varied between 20-1728 ind.l-1 at pond A, 42-4082 ind.l-1 at pond B and 148-2447 ind.l-1 at pond C. The maximum zoo-heleoplankton abundance was found in the pond with cyanobacteria bloom during Autumn 1994 and the minimum abundance was found in the one with a predominance of E. crassipes. The rank of species richness was pond A > pond B > pond C. Rotifera was the most abundant group in pond A whereas the larval stages of Copepoda were abundant in the other two ponds. Anuraeopsis navicula Rousselt 1910 was the dominant population in the pond with macrophytes prevalence. Brachionus calyciflorus Pallas 1776 and larval stage of Copepoda had variable proportions in the pond with cyanobacteria bloom. Thermocyclops decipiens (Kiefer 1929) was present during the annual cycle only in the pond with organic matter deposited in the bottom. The succession of taxa was observed in the pond with coverage of aquatic macrophytes and with cyanobacteria bloom. Differences in species richness and low similarity in zoo-heleoplankton between ponds were determined by differences in the quality of the water in relation to the presence of macrophytes, cyanobacteria, organic matter deposited in the bottom and fish predation. Multiple regression analysis (stepwise) revealed that water transparency, dissolved oxygen and conductivity were the environmental variables that explained more than 42% of variability in the abundance of the dominant species. Rev. Biol. Trop. 56 (3): 1135-1147. Epub 2008 September 30.

La finalidad del presente estudio fue comparar la abundancia y riqueza de especies del zoo-heleoplancton mayor de 53 µm, en un ciclo anual bajo condiciones climáticas similares en tres estanques artificiales, con el propósito de observar los cambios durante un ciclo anual. Las muestras fueron tomadas mensualmente desde junio de 1993 hasta julio de 1994 en Corrientes, Argentina. El primer estanque (A) estuvo cubierto un 80% por E. crassipes, el segundo estanque (B) con floraciones de M. aeruginosa y el tercer estanque (C) con materia orgánica depositada en el fondo. El agua fue más ácida en el estanque A y tuvo más concentración de oxígeno disuelto en el B. La densidad del zoo-heleoplancton fue variable entre 20-1728 ind.l-1 en el estanque A, 42-4082 ind.l-1 en el estanque B y 148-2447 ind.l-1 en el estanque C. El rango de la riqueza de especies fue estanque A> estanque B> estanque C. La máxima abundancia del zoo-heleoplancton se encontró en el estanque con floraciones de cianobacterias y la mínima entre macrófitas de E. crassipes. Rotifera fue el grupo más abundante en el estanque con presencia de macrófitas. Los estadios larvales de Copepoda fueron abundantes en los estanques con materia orgánica depositada en el fondo y con dominancia de cianobacterias. A. navicula fue la población dominante en el agua libre del estanque con predominio de macrófitas. B. calyciflorus y estadios larvales de Copepoda tuvieron proporciones variables en el estanque con cianobacterias. T. decipiens fue la única población presente en el estanque con materia orgánica depositada en el fondo. Se observó un patrón de sucesión de los taxa en el estanque con importante cobertura de macrófitas acuáticas y con floraciones de cianobacterias. Las diferencias en la riqueza de especies y la baja similitud del zoo-heleoplancton entre los estanques estuvieron determinadas por la calidad del agua en relación con la presencia de macrófitas, cianobacterias, materia orgánica depositada en el fondo y peces. El análisis de regresión múltiple (stepwise) reveló que la transparencia del agua, el oxígeno disuelto y la conductividad fueron las variables ambientales que explican más de 42% de variabilidad en la abundancia de las especies dominantes.

Zoo-heleoplankton structure in three artificial ponds of North-eastern Argentina.

The aim of the present study was to compare the abundance and species richness of zoo-heleoplankton bigger than 53 microm in an annual cycle under similar climate conditions in three artificial ponds, in order to observe the changes during an annual cycle. Samples were taken monthly from June 1993 to July 1994 in Corrientes, Argentina. The first pond (A) was covered an 80% by Eichhornia crassipes (Mart.), the second one (B) with bloom of Microcystis aeruginosa (Kurtzing) and the last one (C) with organic matter deposited in the bottom. The water was more acidic at pond A, and the water at pond B contained more dissolved oxygen concentration than the water at the other two ponds. The zoo-heleoplankton densities varied between 20-1728 ind.l(-1) at pond A, 42-4082 ind.l(-1) at pond B and 148-2447 ind.l(-1) at pond C. The maximum zoo-heleoplankton abundance was found in the pond with cyanobacteria bloom during Autumn 1994 and the minimum abundance was found in the one with a predominance of E. crassipes. The rank of species richness was pond A > pond B > pond C. Rotifera was the most abundant group in pond A whereas the larval stages of Copepoda were abundant in the other two ponds. Anuraeopsis navicula Rousselt 1910 was the dominant population in the pond with macrophytes prevalence. Brachionus calyciflorus Pallas 1776 and larval stage of Copepoda had variable proportions in the pond with cyanobacteria bloom. Thermocyclops decipiens (Kiefer 1929) was present during the annual cycle only in the pond with organic matter deposited in the bottom. The succession of taxa was observed in the pond with coverage of aquatic macrophytes and with cyanobacteria bloom. Differences in species richness and low similarity in zoo-heleoplankton between ponds were determined by differences in the quality of the water in relation to the presence of macrophytes, cyanobacteria, organic matter deposited in the bottom and fish predation. Multiple regression analysis (stepwise) revealed that water transparency, dissolved oxygen and conductivity were the environmental variables that explained more than 42% of variability in the abundance of the dominant species.

Predatory - prey relationships in subtropical zooplankton: water mite against cladocerans in an Argentine lake.

In a small lake in northern Argentina pelagic water mite Piona sp. had the maximum of population density in January following with a five-day delay after the peak of zooplankton dominant - Daphnia laevis. The mite density was highly predicted by the previous variations of Daphnia density during 4 months of observation (December-March). Daphnia density was a negative delayed function of the predator density but only in December-January when Piona was abundant. During that period Daphnia death rate, d was also correlated with the mite density (r 2=0.80, P<0.005). In laboratory experiments water mites killed 1-7 Daphnia · predator-1 · hour-1 in a broad range of prey density. Another zooplankton component, Diaphanosoma birgei, was consumed at the same rates. The mite hardly consumed any copepods. In the pelagium during 24 hours the mite was more associated with Daphnia, than with Diaphanosoma, probably, because of the coincidence in photoreactions with Daphnia. Piona contribution to the death rates of its prey estimated by using the data on functional and numerical responses as well as by means of Edmondson-Paloheimo model, could reach 53% for Daphnia and 40% for Diaphanosoma. A computer experiment on the reconstruction of prey dynamics after subtraction of predator influence showed that the mite could have caused a depression in Daphnia numbers observed in the lake, but the declines in Diaphanosoma population were caused by other factors. After the "removal" of mite pressure model Daphnia population increased its average density 10-fold. Experiments on Piona feeding revealed a strong effect of interference among predators. This was eliminated by putting one mite per experimental vessel, which led to a 20-fold increase in predation rate. The effect explains the low feeding rates of Piona obtained by the previous authors who ignored the possibility of interference.