Luciana Montalto

Cyst formation in tubificidae (Naidinae) and opistocystidae (Annelida, Oligochaeta) as an adaptive strategy for drought tolerance in fluvial wetlands of the Paraná River, Argentina

During a broad study of invertebrate colonization in marginal fluvial wetlands of the Middle Paraná River in Argentina, cyst formation was observed in two of the 26 species of aquatic oligochaetes identified from the study—Dero multibranchiata Steiren, 1892 (Tubificidae, Naidinae), andTrieminentia corderoi (Harman, 1969) (Opistocystidae). All specimens of the two species in which cyst formation was observed had been collected after drying conditions ranging from 14 to 28 days. A clitellum was not observed in any of the specimens collected. Lengths of specimens ranged from 0.88 mm to 2.84 mm inDero multibranchiata and 2.25 mm to 2.40 mm inTrieminentia corderoi. The development of protective cysts byDero multibranchiata andTrieminentia corderoi, and perhaps many other species of aquatic oligochaetes, appears to be an adaptive strategy enabling them to survive drought in temporary wetlands, recolonize freshwater habitats upon inundation, and disperse both laterally and downstream with rising water levels in wetlands and streams.

Sampling and Processing Aquatic and Terrestrial Invertebrates in Wetlands

Obtaining unbiased samples of aquatic and terrestrial invertebrates from wetlands provides unique challenges due to the varied life history strategies of invertebrates as well as the heterogeneity present within a wetland. Many sampling devices are useful in more than one sampling environment within a wetland but the effectiveness of most methods varies among and within wetlands as well as between users. In this chapter, we emphasize field collecting techniques and address laboratory sorting methods. When possible, the advantages and disadvantages of each method are listed and suggestions are provided to reduce bias and unwanted variability in sample collection. Sampling devices for benthic (grabs, single and multiple cores, nets, and artificial substrate), water-column (open cylinder, emergence trap, activity trap, sweep net), epiphytic (box samplers, quadrat samplers), flying terrestrial (aerial net, flight intercept trap, light trap, malaise trap), and non-flying terrestrial (sweep net, aspirator, vacuum sampler, Berlese-Tullgren funnel, mist net) invertebrates are presented and discussed.

Aquatic toxicity of ivermectin in cattle dung assessed using microcosms

Ivermectin (IVM) is a parasiticide widely used for livestock. It is a semisynthetic derivative of avermectin, a macrocyclic lactone produced by Streptomyces avermitilis. This drug is only partly metabolized by livestock; considerable amounts of parent drug are excreted mostly via feces. To simulate exposure of aquatic invertebrates and macrophytes to direct excretion of cattle dung into surface waters, a microcosm experiment with IVM spiked in cattle dung was conducted. The objectives of this study were to characterize accumulation of IVM in water, sediment+dung, roots of the floating fern Salvinia and the zooplankton Ceriodaphnia dubia, the amphipod Hyalella and the apple snail Pomacea; to determine the effect of this drug spiked in cattle dung on life-history traits of these invertebrates; and to evaluate the influence of IVM on aquatic nutrient cycling. Dung was spiked with IVM to attain concentrations of 1150, 458, 50 and 22µgkg-1dung fresh weight, approximating those found in cattle dung at days 3, 7, 16 and 29 following subcutaneous injection. Concentrations found in dung during the first week of excretion were lethally toxic to Ceriodaphnia dubia and Hyalella, whereas no mortality was observed in Pomacea. Concentrations of IVM in roots, sediment + dung and Pomacea increased significantly from the lowest to the highest treatment level. The effect of this drug on decomposition and release of nutrients from dung would have negative consequences for nutrient cycling in water. Increasing concentrations in sediment + dung with days of the experiment suggested that toxic concentrations would persist for an extended period in the water-sediment system. IVM represents an ecological risk for aquatic ecosystems, underscoring the need for livestock management strategies to limit its entry into water bodies.

The Application of Chironomid Pupal Exuvial Technique (CPET) for Ecological Analysis in a Neotropical Large River System

This field ecological study, based on the chironomid pupal exuvial technique (CPET), is new for the Paraná River and proposes an efficient tool to be used in future ecological approaches and biomonitoring. Drifting of pupal exuviae in a river-floodplain system of the Middle Paraná River floodplain was represented by 34 Chironomidae taxa, being the characteristic association obtained from the CPET: Lopescladius, Onconeura, Paralauterborniella, Polypedilum, and Harnischia complex. Diversity, richness, dominance, total density, and density of dominant taxa were different between the longitudinal and lateral dimensions but not between hydrologic phases, with a greater diversity and richness in the main channel of the river and higher density and dominance in floodplain habitats. The species turnover is the dominant process in structuring studied assemblages in spatial and temporal analysis, increasing in the floodplain habitats and in low-water phase. The results obtained showed that drifting exuviae in the longitudinal axis were coming from different assemblages and environments of a wider area (regional), while exuviae recorded in the connections of the floodplain environments in the lateral dimension could reflect the local assemblages. We demonstrated the ecological value of CPET studies to interpret the attributes of Chironomidae assemblage in river-floodplain systems of large rivers in an integrated way.