Diel variation of aquatic insect drift in streams of Southern Brazil

Some organisms, such as aquatic insects, are transported from the upstream to downstream region of streams through a process called drift. This process occurs in passive and active ways and can be variable throughout the day, mainly between the nocturnal and diurnal periods. Here, we evaluate the periodicity of the drift of aquatic insects in two streams of the Middle Iguaçu basin, southern region of Brazil. We predicted that the drift of aquatic insects brings the highest richness, diversity and abundance during the nocturnal period, compared to the diurnal period. In addition, we expected that the composition of species is different between these periods. In each stream, aquatic insect sampling was carried out 10 times, for 24 hours, using drift nets. A total of 2,114 aquatic insect specimens were recorded, distributed in 26 families. Of these families, 20 were recorded during the diurnal period and 24 during the nocturnal period. Our results showed an increase in the diversity and abundance of aquatic insect drift in the nocturnal period. However, only abundance was significantly different between the periods. We attribute the higher abundance in nocturnal drift possibly to biological interactions. Thus, nocturnal drift can be a strategy of some aquatic insects to avoid visual predation by other invertebrates and/or vertebrates, in Neotropical streams. We highlight the importance of our study, because it can be used for comparison in surveys of lotic environments that have been impacted by human activity (e.g. by dam construction), which can alter the water flow, and consequently the pattern of insect drift.

The invertebrate's community in adjacent Alto Iguaçu's anthropic lakes of different environmental factors / A comunidade de invertebrados em lagos antrópicos adjacentes com diferentes fatores ambientais no Alto Iguaçu

Environmental differences occur between lentic and lotic communities' establishment, especially because of water time residence. Here we used a combination of field measurements and statistical analysis to evaluate the influent factors on the aquatic macroinvertebrates' composition and structure in 15 anthropogenic lakes from Alto Iguaçu's region. Macroinvertebrates were sampled from the marginal vegetation (with or without macrophytes) and sediment. Chemical parameters ranged among the anthropogenic lakes, mainly those which are connected to the Iguaçu River, beyond the presence or absence of macrophytes, interfering on the community's structure. Lake's morphometric data were measured in each lake and its relation to community was tested. The community structure was not related to the margin development index (Ds), macrophytes and altitude. Higher equitability was associated to the macrophytes presence in more than 30% of water surface and also where the riparian vegetation was more complex. Chironomids and oligochaetes densities were associated to lakes with the water surface completely covered by macrophytes and complex riparian vegetation. We observed a close association between productivity (phosphorous and nitrogen) and the community equitability (R = 0.3; p < 0.05) and Oligochaeta dominance (R = 0.32; p < 0.05), and not to Ostracoda's (R = 0.33; p > 0.05) and Chironomidae's (R = 0.34; p > 0.05) dominances, although we had not weighty difference among analyzed biological indexes. The obtained values from the BMWP' and EPT indexes resulted in acceptable, doubtful or critical water quality, what corroborates with the macroinvertebrate's structure of the composition and with the environmental variables observed in field.

Diferenças ambientais ocorrem entre o estabelecimento de comunidades de ambientes lênticos e lóticos, especialmente por causa do tempo de residência da água. Foi usada uma combinação de métricas de campo e análise estatística para avaliar os fatores influentes sobre a composição e estrutura de macroinvertebrados aquáticos em 15 lagos antropogênicos da região do Alto Iguaçu. Os macroinvertebrados foram amostrados da vegetação marginal (com ou sem macrófitas) e sedimento. Parâmetros químicos variaram entre os lagos antrópicos, principalmente aqueles conectados ao Rio Iguaçu, além da presença ou ausência das macrófitas, interferindo na estrutura da comunidade. Dados de morfometria de lagos foram mensurados e sua relação com a comunidade foi testada. A estrutura da comunidade não foi relacionada ao índice de desenvolvimento da margem (Ds), macrófitas e altitude. Maior equitabilidade foi associada à presença de macrófitas em mais de 30% da superfície da água e também onde a vegetação ripária foi mais complexa. Densidades de quironomídeos e oligoquetas foram associadas a lagos com a superfície completamente coberta por macrófitas e complexa vegetação ripária. Foi observada associação entre a produtividade (fósforo e nitrogênio) e a equitabilidade da comunidade (R = 0.3; p < 0.05) e dominância de Oligochaeta (R = 0.32; p < 0.05) e não para a dominância de Ostracoda (R = 0.33; p > 0,05) e Chironomidae (R = 0.34; p > 0.05), apesar de não haver diferença entre os índices biológicos analisados. Os valores obtidos através do Índice BMWP' e EPT/C resultaram em ambientes de qualidade aceitável, duvidosa ou crítica, o que corrobora com a estrutura da composição de invertebrados e com as características ambientais observadas em campo.