Abstract
The fluctuation of the population of Daphnia laevis in Lake Jacaré (Middle River Doce, Minas Gerais) was monitored monthly (at one point in the limnetic region) for six years (2002-2007) as part of the Program of Long-Term Ecological Research (LTER/UFMG). The following parameters were also monitored: water temperature, pH, electrical conductivity, dissolved oxygen, chlorophyll a, total phosphorus, phosphate, total nitrogen, nitrate, nitrite, ammonia, and densities of Chaoborus and ephippia of Daphnia laevis in the sediment. A seasonal pattern was observed in the fluctuation of D. laevis, with higher densities recorded during periods of circulation (May-August). A significant correlation was found between the density of D. laevis and temperature (r = -0.47, p = 0.0001), chlorophyll-a (r = -0.32, p = 0.016) and indicators of the lake's trophic status (total phosphorus, r = 0.32, p = 0.007 and trophic state, r = 0.36, p = 0.003), as well as Chaoborus density (r = 0.43 and p = 0.002). These results indicate that changes in the physical and chemical characteristics of the water related with stratification and circulation of the lake may have a direct (temperature, total phosphorous) or an indirect (food availability, presence of predators, ephippia eclosion) influence on the fluctuation of the D. laevis population.
Highlights
Zooplankters are short life-cycle organisms that are sensitive to environmental variations (Fryer, 1996; Crispim and Watanabe, 2000)
A clear seasonal pattern for Daphnia laevis in Lake Jacaré was found, with a consistent increase in the population during the circulation periods. This population was greatly influenced by the annual temperature fluctuation during the six years of study
Temperature is an important environmental factor affecting zooplankton communities. 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)
Summary
Zooplankters are short life-cycle organisms that are sensitive to environmental variations (Fryer, 1996; Crispim and Watanabe, 2000). Environmental conditions (such as temperature, dissolved oxygen, pH, and others) are important factors that act directly on the structure of the zooplankton community, changing the spatial and temporal distribution of the species (Bottrell, 1975; Vijverberg et al, 1996; Gyllström et al, 2004). 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
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