Florencia Lucila Zilli

Patterns in macroinvertebrate assemblages at different spatial scales. Implications of hydrological connectivity in a large floodplain river

The habitat heterogeneity generated and sustained by the connectivity of floodplain habitats, the seasonal flood pulse, and the variability of the physical structures typically found in floodplains of large rivers results in a variable space–time mosaic of water sources that results in a high biodiversity of the river-floodplain system. In order to assess the implications of natural connectivity and the heterogeneity on the patterns of macroinvertebrate assemblages at different spatial scales, monthly samplings in six different mesohabitats (lakes with different hydrological connection and secondary channels with permanently and intermittent flow) of the Paraná River floodplain were performed from April 2005 to March 2006. The mesohabitats had different granulometry and detritus composition of their bottom sediments. They also had different conductivity, transparency, and depth in relation to the different connectivity degrees. Mesohabitats differed in the abundance of macroinvertebrates of different taxonomic groups and diversity. The environmental variables were correlated to the patterns of macroinvertebrate abundance, with dominance of different species of annelids and mollusks at the patch, mesohabitats, and island scales. An alpha diversity gradient from the isolated lake (65 taxonomic units) to the secondary channels (25 taxonomic units) was obtained. The analyzed mesohabitats showed a high taxa turnover, with high values not only among the mesohabitats located in the different islands, but also among the mesohabitats in relation to different connectivity degrees. The mesohabitats showed negative co-occurrence of macroinvertebrate assemblages. The spatial heterogeneity, sustained by the connectivity degree, played a key role in structuring benthic assemblages at different scales, positively influencing the regional diversity.

Diet and functional feeding groups of Chironomidae (Diptera) in the Middle Paraná River floodplain (Argentina)

The gut contents of nine genera of benthic Chironominae and Tanypodinae from the Middle Parana River floodplain habitats (a lake and a secondary channel) were analyzed to determine their feeding patterns and functional feeding groups. Amorphous detritus, animal and vegetal tissues, and mineral materials (predominantly sand) were observed in the larval guts. Amorphous detritus were the main food item found for Polypedilum (Tripodura) sp., Chironomus gr. decorus sp., Endotribelos sp., Phaenopsectra sp., Cladopelma sp., and Pelomus sp. (Chironominae), while animal tissues (mainly oligochaetes) were the most important food item found for Ablabesmyia (Karelia) sp., Coelotanypus sp., and Procladius sp. (Tanypodinae). Dietary overlap was calculated for all pairs of genera. Within predators, the highest overlap was obtained between Coelotanypus sp. and Ablabesmyia (Karelia) sp., while within detritivores the highest niche overlap was obtained between Endotribelos sp. and Phaenopsectra sp.

Trophic level, food chain length and omnivory in the Paraná River: a food web model approach in a floodplain river system

To determine the mean trophic level and food chain length and to quantify omnivory in a floodplain lake of the Middle Paraná River, we constructed a food web model based on available data. Because proper selection of basal resources is essential, we performed stepwise model selection to decide which sources to include in the model. We estimated mean trophic level, food chain length and omnivory using a binary web (non-weighted trophic links) and a weighted web (trophic links weighted using stable isotopes). Model selection excluded macrophytes as relevant resources for the food web of this floodplain lake. In general, trophic links were relatively even, leading to similar estimations of mean trophic level and omnivory in both binary and weighted webs. Food chain length, however, was higher for the binary web, which was caused by the strong link of top predators with lower-trophic level prey in this ecosystem. Overall, the estimate of food chain length in the Paraná River was not particularly high, despite the high productivity and size of this ecosystem. We suggest that the periodical hydrological fluctuations of large rivers could be a major factor precluding the occurrence of long food chains.

Life cycle of Goeldichironomus holoprasinus goeldi (Diptera: Chironomidae) in laboratory

The larvae of Chironomidae are very important due to their density and role in aquatic food webs. Goeldichironomus holoprasinus Goeldi is one of the most abundant species of Chironomidae in man-made and natural systems, being widely used in water quality assessments. Because of its tolerance to stressing environmental factors, many studies have investigated the effects of stressors on G. holoprasinus anatomy and bionomic attributes. The main aim of this work was to describe G. holoprasinus life cycle attributes in laboratory conditions. The cephalic capsule growth among instars was 1.64 in average (Dyar proportion), whereas the total size growth was continuous. The average room temperature registered was 26 degrees C (18-33 degrees C). In this conditions the D value (time from oviposition to first imago emergence) was 13 days, whereas the minimum G value (interval from the oviposition to the first progeny of the next generation) was 16 days. The emergence lasted four days, which determined that average G of 18 days. Thus, at registered temperatures G. holoprasinus has a short life cycle.

Ecological Responses to Different Degrees of Hydrologic Connectivity: Assessing Patterns in the Bionomy of Benthic Chironomids in a Large River-Floodplain System

Floodplain wetlands of the Middle Paraná River, Argentina, are regulated by their hydrologic connectivity to the main channel as well as by their position within the river network. The Chironomids are the most abundant insects that inhabit the benthos of the Paraná River floodplain habitats. In order to address whether wetlands with different degrees of connectivity (disconnected, temporarily, and permanently connected) exhibit different abundance patterns and secondary production of benthic chironomids, samples were collected during a year comprising high and low water phases. The disconnected wetland exhibited the highest abundance and secondary production of chironomids. Both attributes were positively correlated to the degree of connectivity for most of the predators among the connected wetlands. Differences in assemblages’ composition and secondary production were found to be in relation to the degree of connectivity, the cover of macrophytes, the detritus at the bottom, the transparency of water, the proportion of clay in bottom sediments and the location of wetlands within the floodplain. The interaction between local environmental factors mediated by lateral connectivity and regional dynamics of metapopulations established diverse patterns in the metrics of chironomids along the Paraná River floodplain wetlands. Thus, various degrees of hydrologic connectivity of wetlands should be preserved to maintain a high productivity of different chironomids in the floodplain.

Life history traits and secondary production of Campsurus violaceus (Ephemeroptera: Polymitarcyidae) in the Paraná River floodplain lakes, Argentina

Campsurus nymphs are among the most abundant mayflies in neotropical aquatic habitats. The abundance patterns and secondary production of Campsurus violaceus were analyzed monthly from April 2005 to March 2006 in lakes with different degrees of connectivity in the floodplain of the Middle Paraná River. Significant differences were estimated for the abundance and secondary production of the species among the studied lakes. The patterns in the abundance of nymphs were correlated to substrate characteristics (type of substrate, content of detritus), water transparency, and conductivity of lakes and the variations in the life cycle were related to temperature. Degree of connectivity of lakes was the main factor in determining differences among populations, as it influenced local conditions, finally determining regional dissimilarities in abundance pattern and secondary production for the species. Las ninfas de Campsurus se encuentran dentro de las efímeras más abundantes en ambientes acuáticos neotropicales. Se analizaron los patrones de abundancia y la producción secundaria de Campsurus violaceus en lagunas con diferente nivel de conectividad mensualmente entre Abril de 2005 y Marzo de 2006. Se estimaron diferencias significativas entre las lagunas estudiadas en la abundancia y producción secundaria de la especie. Los patrones de abundancia de ninfas se correlacionaron con las características del sustrato (tipo de sustrato, contenido de detrito), transparencia del agua y conductividad de las lagunas y las variaciones en el ciclo de vida se relacionaron con la temperatura. El nivel de conectividad fue el factor principal en determinar diferencias entre las poblaciones al influenciar las condiciones locales, determinando disimilitudes regionales en el patrón de abundancia y en la producción secundaria de la especie.

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.

Redescription of two species of Coelotanypus ( Kieffer ) 1913 (Diptera: Chironomidae) in rivers of the Parano-Platense basin (Argentina, South America)

Male imagos of Coelotanypus delpontei (Edwards) are redescribed and newly figured and the immature stages are described and figured for the first time. During this study, male imagos of C. mendax (Lynch Arribalzaga) are also redescribed. The specimens were collected from the Paraná and near Uruguay rivers in the Parano-Platense basin.

Figures 14–16 In Redescription Of Two Species Of Coelotanypus (Kieffer) 1913 (Diptera: Chironomidae) In Rivers Of The Parano-Platense Basin (Argentina, South America)

FIGURES 14–16. Coelotanypus mendax (Lynch Arrib.) Edwards, male. 14, wing (scale= 500 µm); 15,, color pattern of legs, a,anterior; b, mid; c, hind; 16, color pattern of abdominal tergites.