Predation on and by pelagic Turbellaria in some lakes in Brazil

Abstract

Planktonic Turbellaria are of common occurrence in both natural and man-made lakes in Brazil . Experiments were performed in 1987 and 1989 to determine which zooplankton species are consumed by predatory Mesostoma sp. from three natural lakes in the Rio Doce Valley . Experiments were also performed in 1989 with a yet unidentified flatworm from Barra Bonita reservoir . Both predators consumed Daphnia and Ceriodaphnia at a high rate: 4 individuals per day in the case of Mesostoma sp., a large species and 1 .5 ind day -' in the case of the smaller species from Barra Bonita reservoir . Consumption of copepod nauplii, copepodids and adults was much lower, and Ostracoda were not consumed at all . Experiments on food selectivity showed a clear preference by the flatworms for cladocerans .In the lakes studied, flatworms are heavily preyed upon by larvae of Chaoborus and by Mesocyclops species .Turbellaria densities in the natural lakes were around 300 individuals per cubic meter, whereas in Barra Bonita reservoir, 1000 individuals per cubic meter was a mean value in a fifteen days study .

Fluctuations of the population of Daphnia laevis Birge 1878: a six-year study in a tropical lake

“…It is well-known that the increase in temperature can reduce the generation time and life cycle of several organisms, as well as increase the reproduction and filtration rates of many species (Edmondson, 1965;Rocha et al, 1990;Bunioto and Arcifa, 2007). However, a negative correlation between the D. laevis density and temperature was observed in Lake Jacaré, indicating that the natural fluctuation of this species can also be widely influenced by changes in water temperature, even if in a thermal range considered suitable for tropical cladocerans.…”

“…Furthermore, biotic factors, such as predation (Brooks and Dodson, 1965;Rocha et al, 1990), competition (Smith and Cooper, 1982), food availability and quality, within others, have an enormous pressure on the populations.…”

“…In the tropics, despite the small annual temperature fluctuations, population responses can be observed (Bunioto and Arcifa, 2007). This variable can influence zooplankton in two ways: directly, on the reproduction rates, filtration rates, duration of the life cycle, production and hatching of resistance eggs (Rocha et al, 1990;Crispim and Watanabe, 2000;Bunioto and Arcifa, 2007); or indirectly, through thermal stratification. This phenomenon creates a larger spatial heterogeneity, also causing a "zooplankton stratification", where the organisms group according to the best environment conditions or because they cannot overcome the physical-chemical barriers (Thackeray et al, 2006).…”

Microturbellarians (Platyhelminthes and Acoelomorpha) in Brazil: invisible organisms?

“…Freshwater forms may occur in temporary or permanent wetlands, such as lakes, natural or artificial ponds, pools, ditches, streams and rivers (Kolasa, 1991;Noreña-Janssen, 1995;Young, 2001), as well as in agroecosystems (Bambaradeniya et al, 2004;Vara and Leal-Zanchet, 2013). Some marine flatworms, such as acoels and polyclads, and freshwater rhabdocoels are planctonic (Hyman, 1951;Rocha et al, 1990;Dumont et al, 2014). Some microturbellarians may occur in humid terrestrial environments (Hyman, 1951;Tessens et al, 2014); land triclads may be a species-rich group in tropical and subtropical ecosystems (Carbayo et al, 2009).…”

“…Later, Rocha et al (1990) and Hooge and Rocha (2006) studied, respectively, freshwater rhabdocoels and acoels from the state of São Paulo. In addition, a new species of marine rhabocoel was recently described (Reygel et al, 2014).…”