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

Abstract

Environmental disturbance on freshwater ecosystems significantly impacts all levels of the trophic web. Salinity in lentic freshwater ecosystems, as a consequence of climatic changes, is rising concern in the scientific community. These alterations affect water quality, the composition and diversity of the aquatic communities. This study aimed to assess the seston quality of two lentic ecosystems, Crestuma reservoir and lake Vela, and evaluate the effects of salinity on food performance of Daphnia magna and Daphnia longispina (isolated from the referred ecosystems). Feeding inhibition tests were used to conduct these two evaluations. Physical and chemical water classification revealed a poor or good ecological potential of the two lentic ecosystems, according to WFD approach. To evaluate seston quality, filtered and unfiltered water samples from the lentic ecosystems were used as treatments. Although only summer samples from Crestuma presented good water quality, the results from the feeding inhibition tests showed that seston from lake Vela presented more nutritional quality. Concerning the assay to evaluate the salinity effect on Daphnia spp., a significant reduction in the filtration rate was observed. The NOEC value was 0.7 g/L NaCl and 0.8 g/L NaCl for D. magna and D. longispina C and V, respectively. The LOEC value was also distinct between species, being 1.0 g/L and 0.9 g/L, respectively. This work allowed to verify that feeding inhibition tests are not sensitive enough for assess the quality of natural waters. However, these tests are economically viable and have high sensitivity to evaluate NaCl effects on Daphnia spp.

Evidence for Links between Feeding Behavior of Daphnia magna and Water Framework Directive Elements: Case Study of Crestuma-Lever Reservoir

“…These results are in agreement with the results presented here, namely, for the September samples. In addition, in the spring sampling, Queirós et al [13] did not observe differences in the feeding rates, suggesting that the phytoplankton present in the water samples are of good quality for D. magna.…”

“…Indeed, the biomass phytoplankton indicator quantified [chlorophyll-a] does not allow us to know the quality and diversity that occur, which may not be palatable for the higher trophic levels. Queirós et al [13] evaluated the feeding rates of Daphnia spp. after exposure to water samples from the Crestuma reservoir and concluded that, at the end of summer, the seston does not have a good nutritional quality (e.g., due to a higher amount of cyanobacteria) for D. magna.…”

“…In this month, a substantial increase in the ammonia concentration was observed, which may have also affected the D. magna feeding performance. Indeed, Queirós et al [13] have already shown that ashes leaching can cause alterations in the nutrient and phytoplankton dynamics in lentic ecosystems.…”

“…Daphnia magna is a small zooplanktonic crustacean, used as a standard species in ecotoxicological studies [8,9], namely in bioassays required by national and European legislation for the ecotoxicological assessment of new chemical agents, urban and industrial effluents, and freshwater ecosystems [10]. The diversity of the quantity of the diet provided to Daphnia, and other cladocerans, has been the subject of some studies (e.g., [11]), through the effects evaluation of feeding behavior assays after exposure to different stressful situations (e.g., pharmaceuticals, pesticides, and metals) [2,12,13]. These assays offer a very sensitive and ecologically relevant diagnosis for use in water quality assessment [12] as several authors have already demonstrated that the presence of contaminants and other seston components can affect the feeding rate of these organisms [14,15].…”

Perspective Chapter: Daphnia magna as a Potential Indicator of Reservoir Water Quality – Current Status and Perspectives Focused in Ecotoxicological Classes Regarding the Risk Prediction

“…2.5.2 D. magna feeding rate assays D. magna feeding rate assays were conducted according to [22] with some adaptations described in [9]. For each water sample, bioassays were performed on 6-well ), Total Kjeldahl nitrogen (N Kj ), Total phosphorus (P total ), Arsenic (As), Zinc (Zn), Copper (Cu), Cadmium (Cd), Mercury (Hg), Nickel (Ni), Lead (Pb), Calcium (Ca), Magnesium (Mg), Iron (Fe), Manganese (Mn), and Ecological Quality Ratio (EQR).…”