Cristiane Biasi

Effects of agricultural and urban impacts on macroinvertebrates assemblages in streams (Rio Grande do Sul, Brazil)

This study evaluates the effects of agricultural and urban activities on the structure and composition of benthic communities of streams in the state of Rio Grande do Sul, Brazil. Benthic macroinvertebrates were collected in streams influenced by urbanization and agriculture and in streams with no anthropogenic disturbances (reference streams). Organism density was superior in urban streams when compared with streams in the other two areas. The taxonomic richness and Shannon diversity index were higher in reference streams. The benthic fauna composition was significantly different among land uses. The classification and ordination analyses corroborated the results of variance analyses demonstrating the formation of clusters corresponding to streams with similar land use. Seasonality was also found to influence the benthic community, though in a lesser degree than land use.

Distribution of aquatic insects in urban headwater streams

AIMS: The objective of this study was to evaluate the effects of urban environments on the distribution and occurrence of aquatic Ephemeroptera, Plecoptera and Trichoptera (EPT) insects in six urban subtropical streams; METHODS: Organisms were collected with a Surber sampler in 2005 and 2006, over two hydrological cycles. We analyzed abundance values, taxonomic richness, Shannon-Wiener diversity and Pielous evenness. A principal components analysis (PCA) was performed to evaluate the environmental variability of streams. A canonical correspondence analysis (CCA) was performed to evaluate the possible effects of environmental variables; RESULTS: The PCA ordered the streams according to their quality, and Suzana and Nadau streams had higher concentrations of nutrients. The Baetidae (Ephemeroptera) was the family with the highest number of genera (18). Perissophlebiodes Savage, 1983, and Americabaetis Kluge, 1992, were the most common genera. Anacroneuria Klapalek, 1909, was the most abundant Pleocoptera, and Smicridea McLachlan, 1871, was the dominant Trichoptera genus. In the CCA, pH, electrical conductivity and stream velocity were positively correlated with axis 1, whereas dissolved oxygen was negatively correlated with axis 1; CONCLUSIONS: Our results show that the distribution of EPT in urban streams is affected by changes in water physicochemical characteristics. However, these changes are not sufficiently severe to cause the elimination of EPT.

The effect of the macroconsumer Aegla longirostri (Crustacea, Decapoda) on the invertebrate community in a subtropical stream

AIM: This study tested whether the macroconsumer Aegla longirostri is able to modify the invertebrate community associated with decomposing leaves. METHODS: The study was performed in a first-order stream located in central Rio Grande do Sul state. Two types of channels containing leaf litter of Ficus luschnathiana were placed in the stream; one type allowed aeglids to access the leaf litter (PA), and the other type did not (AA). Both types allowed aquatic insects to access the leaf litter. In addition, a control treatment (C) was established, in which no channel was used. After 3, 7, 11, 15 and 19 days, a litter bag was removed from each replicate of each treatment. RESULTS: A total of 926 organisms belonging to 19 families were identified. The most common taxon in all treatments was Chironomidae, which comprised 71% of the total and was represented by 16 genera. The presence of aeglids decreased the total abundance of organisms by 89% and the taxonomic richness by 35%. The presence of A. longirostri altered the taxonomic composition of the invertebrates and the structure of the trophic groups, causing a decrease in the abundance of all groups, except for shredders and predators. The gathering-collectors trophic group was the most important (65%), in both the presence and absence of A. longirostri. CONCLUSION: Our study showed that A. longirostri, as well as other macroconsumers, was able to modify the structure of the invertebrate community associated with decomposing leaves in the stream.

Avoid predation or take risks in basic activities? Predator–prey relationship in subtropical streams between decapods and caddisflies

The objective of the present study was to analyse the movement, feeding and case-building behaviours of Phylloicus in the presence and absence of a likely decapod predator, Aegla longirostri. We used aquaria divided by a perforated acrylic plate, with one side containing a Phylloicus and the other containing A. longirostri. Movement was quantified through the time spent in active movement, feeding was quantified through the amount of consumed leaves and the case-building was assessed by comparing the number of leaf discs selected of each plant species. The Phylloicus movement activity was affected by A. longirostri, being higher in the predator absence than in its presence. The caddisfly feeding behaviour was not affected by the presence of the crab. Phylloicus was selective in the choice of plant species for case-building; in the presence of the predator, harder discs were more often employed, whereas softer and less resistant discs were chosen in the absence of the predator. The anti-predator responses of caddisfly demonstrated that they are able to detect the presence of crabs and modify their activities, thereby increasing their chances of survival.

Composition and diversity of the Chironomidae in subtropical streams: effects of environmental predictors and temporal analysis

AIMS: The aims of this study were (i) to evaluate the spatial and temporal distribution of chironomids in subtropical streams and (ii) to investigate the importance of environmental predictors in the distribution of this group. METHODS: Samples were collected in four annual seasons between 2010 and 2011, in 10 streams located in an agricultural matrix in southern Brazil, using a Surber sampler. Organisms were identified to the genus level. Some environmental variables were analysed in the sampling sites of the Chironomidae. The variations in abundance and diversity were compared by Analysis of Variance, whereas the community composition was analysed using Multivariate Analysis of Variance. A Redundance Analysis was used to evaluate the effect of environmental variables on the chironomid community. RESULTS: 7,349 individuals were identified, belonging to three subfamilies (Chironominae, Tanypodinae and Orthocladiinae) and 57 genera. The abundance and richness of the Chironomidae were similar between sites and seasons. However, the composition varied spatially and temporally (p < 0.001). Water temperature, total organic carbon, total nitrogen and carbon:nitrogen ratio were variables that influenced the chironomid community. The genera Thienemanniela, Pentaneura, Paratanytarsus, Parapentaneura, Parametriocnemus, Hudsonimyia, Labrundinea and Larsia were present in summer, whereas Parakiefferiella, Paramerina, Metriocnemus were indicators for winter. CONCLUSIONS: The spatial distribution of chironomids was directly related to the environmental conditions of the sampling sites. The temporal variation in the community followed a pattern in relation to water temperature. The variables physical and chemical operate as environmental filters and thereby alter the chironomid community.