Short-term dynamics of cladocerans in a eutrophic shallow lake during a shift in the phytoplankton dominance

Abstract

-The changes in the dynamics of cladocerans in Lake Vela (Portugal), as well as the morphologic and life history traits of the small-bodied cladoceran Ceriodaphnia pulchella, were studied intensively during one month characterized by deep and fast changes in the phytoplankton community: the beginning of the cyanobacteria dominance. Lake Vela, located in the Mediterranean region, is a polymictic shallow lake exhibiting characteristics typical of an advanced trophic status, namely the permanently turbid water, the reduction in biodiversity and the occurrence of cyanobacteria blooms. The density and composition of the cladocerans populations varied considerably during the short-term period analyzed. Coincident with the increase of cyanobacteria, the density of Daphnia longispina decreased drastically, associated with an increase of Bosmina longirostris and Chydorus sp. The constant density of C. pulchella, even during the cyanobacteria dominance, and the strong relationship found between weight and size, suggests that the low quality of phytoplanktonic food in Lake Vela did not play an important role in its fitness. Besides the small size of C. pulchella, this fact could be also related to its diversified diet. Nevertheless, a closer examination of the life history parameters of C. pulchella revealed a reduction in the fecundity, size at first reproduction, mean size of ovigerous females and maximum size of the population, which suggest an increase of the fish pressure after the decline of Daphnia. C. pulchella showed also a short-life cycle and a fast turnover of individuals, which constitutes also an advantage, allowing a fast adaptive response of the population.

Clonal Variation in Growth Plasticity within a Bosmina longirostris Population: The Potential for Resistance to Toxic Cyanobacteria

“…Bosminids appear to be less affected by toxic cyanobacteria than daphniids [30]. With the onset of cyanobacterial blooms, daphniid abundance decreases drastically, and this is associated with an apparent increase in bosminids [31]. In the present study, we ask the following questions: (1) Are there clonal variations in growth plasticity within a bosminid population when phytoplankton composition in summer shifts toward greater dominance by cyanobacteria?…”

Feeding inhibition tests as a tool for seston quality evaluation in lentic ecosystems: salinization impact

“…Several studies already demonstrated that this lake shows high levels of nitrates and phosphates, characteristics of eutrophic ecosystems, mainly due to the regular nutrient inputs from intense agricultural and livestock activities in the adjacent areas (Abrantes et al, 2006;Figueiredo et al, 2006;. Lake Vela is also characterized by an high turbidity water, without a spring clear water phase, and algal blooms are frequently observed in the warmer seasons (Abrantes et al, 2009). microalgae), with a small size and a very characteristic morphology (Figure 3).…”

Limnological variations of a deep reservoir in periods with distinct rainfall patterns

“…This means that annual zooplankton succession is not only related with rainfall events but depends as well on other complex interactions of several key factors. Examples could be the shifts in competitive interactions that may occur between the studied species and between those and rotifers, in edible phytoplankton assemblages (Abrantes et al, 2009) (Rey, 1984;Godlewska et al, 2003;Romare et al, 2005). This fact could have affected the recruitment of some species.…”

“…Consequently, zooplankton is constantly exposed to a great variation of environmental factors, whose fluctuations constrain the size, reproduction and survival of populations. Because of its quick response to environmental change, zooplankton can be regarded as an indicator of disturbance events (Lampert and Sommer, 1997;Jeppesen et al, 1999;Pereira et al, 2002;Abrantes et al, 2009;Obertegger et al, 2010). Therefore, zooplankton can be directly or indirectly influenced by precipitation events.…”