Seasonal, discharge‐driven patterns of mayfly assemblages in an intermittent Neotropical stream

Abstract

1. Streams in the seasonal wet and dry tropics have highly dynamic discharge regimes. Our study stream, located in mid‐western Brazil, drains into the Pantanal, South America’s largest wetlands, and is characterized by frequent spates in the rainy season and several weeks of interrupted flow in the dry season. 2. In order to understand how these seasonal flow patterns influence the aquatic fauna, floating litter was studied because: (i) this habitat is exposed to the current, and thus is likely to be most affected abiotically and biotically by changes in flow; and (ii) this habitat is abundant in unaltered tropical streams. Studies were conducted in a third‐ and a fourth‐order reach. Mayflies were chosen as study organisms because they were frequent and species‐rich on floating litter, and because they should to be responsive to changes in current velocity. 3. In the course of 15 months, covering one rainy and two dry seasons, mayflies showed pronounced seasonal patterns at family and genus level, which were evidently driven by discharge. Two periods of high mayfly densities were observed in the course of one year. One maximum coincided with the peak of the rainy season, the other with the peak of the dry season, and both were distinct in faunistic composition. At high current velocities the leptophlebiid Farrodes sp. was dominant and Leptohyphes sp., Acerpenna sp. and Paracloeodes sp. were frequent. In the dry season, when the river was reduced to isolated standing waters, 86–93% of all mayflies were Caenis sp. 4. Altogether sixteen mayfly genera from the families Baetidae, Caenidae, Leptohyphidae, Leptophlebiidae and Oligoneuriidae were recorded. Two genera are new to science, the baetid Aturbina was recently described (among others, from material from our study river), Acerpenna and Paracloeodes are new records for South America, and Miroculis and Terpides are recorded for the first time south of the Amazon.

Effects of food availability and habitat features on the Ephemeroptera species composition at seasonal and spatial scales from neotropical floodplain rivers

“…and Farrodes sp. Nolte et al (1997), in studies conducted in the Benedict River, reported the occurrence of Caenidae family after a disrupting of water flow. The food resources are another important factor determining the abundance of Caenis sp.…”

The range of insect dormancy responses

“…climatic stresses, habitat stability, predation and competition). Depending on the environment, a focus on response to the seasons throughout the year (see Musolin & Saulich, 1999 for an example of this approach), on seasonal stream discharge (Nolte et al, 1997) or on tidal patterns (Saigusa & Akiyama, 1995) may be appropriate. Some habitats are non-seasonal, because conditions are similar throughout the year except for unpredictable changes (Towns, 1981;Yule & Pearson, 1996).…”

Flux dynamics at the groundwater-surface water interface in a tropical catchment

“…Intermittent streams are inherently variable, with flows typically changing rapidly in response to rain events (Nolte et al, 1997), and can therefore be difficult to adequately characterize. Perennial streams have historically received greater attention than intermittent streams (Boulton and Suter, 1986;Williams, 1988), although recently more attention has been given to the importance of meteorological, geological, and land-cover controls on flows in intermittent streams (Costigan et al, 2015).…”

“…Notwithstanding this previous research, it is clear that our understanding of the hydrological processes controlling flow permanence and interactions between streamflow and aquifer recharge in intermittent river systems needs further improvement (Costigan et al, 2015). This knowledge gap is even more significant for tropical regions, where climate patterns are typically highly dynamic with distinct wet and dry seasons which strongly influence both surface flows and groundwater levels (Costigan et al, 2015;Nolte et al, 1997). The lack of information on intermittent stream dynamics is acute in these tropical areas, as rainfall data is missing or does not capture the high spatial variability because many catchments are ungauged, and no long-term hydrological datasets are available (Klemes, 1993).…”