Population responses and fatty acid profiles of Brachionus calyciflorus (Rotifera) in relation to different thermal regimes.

Diurnal temperature fluctuations affect ectothermic species more than endothermic taxa. We tested the effect of three fixed temperatures (20, 25 and 30 °C) and a 24 h variable (20-30 °C) on the population growth and fatty acid profiles of the common rotifer Brachionus calyciflorus. Depending on the temperature treatment, the peak population abundances of B. calyciflorus varied from 65 to 80 ind./ml, the lowest being on variable temperature range. The rate of population increase varied from 0.31 to 0.52 per day, highest being at 30 °C. There was a curvilinear relationship between the population density and the egg ratio (number of eggs/female) in all the tested temperature regimes. The egg ratio was higher (>0.6) for treatments involving fixed temperatures, but for variable temperature regime, the egg ratios were lower (<0.5). Temperature also induced changes in the fatty acid content of B. calyciflorus. While the total saturated fatty acids increased, both mono-unsaturated and poly-unsaturated fatty acids decreased with increasing temperature regime. These results have been interpreted in relation to the role of temperature (both intensity and mode of exposure) on the population growth characteristics of rotifers.

Demographic responses of Cladocerans (Cladocera) in relation to different concentrations of humic substances.

Cladocerans are constantly exposed to humic substances in nature, yet the effects of these substances on their survival and reproduction are not well known. Here, the effects of humic substances (20 and 40 mg L-1) (HS) on the life history variables of three common cladocerans, Ceriodaphnia dubia, Moina macrocopa, and Daphnia pulex were evaluated. The results showed that the effect of humic substances on the tested cladocerans is species-specific, affecting either survival, reproduction or both. For M. macrocopa, exposed to HS at a concentration of 40 mg L-1, the average lifespan and the life expectancy at birth were significantly reduced as compared to controls, but for C. dubia and D. pulex these parameters were increased. Gross reproductive rate was unaffected by the HS level for both D. pulex and M. macrocopa, but it was significantly higher for C. dubia. When compared to the corresponding controls, for HS-exposed cladocerans, the rate of population increase was significantly reduced in case of D. pulex while it was stimulated for both C. dubia and M. macrocopa. It appears that humic substances had a slightly stronger influence on survivorship than on reproduction of the tested cladocerans.

Four Transgenerational Demographic Performance of Moina macrocopa Exposed to Chronic Levels of Cadmium.

In this study, we quantified intergenerational, demographic variability of Moina macrocopa subjected to cadmium stress. Exposure of M macrocopa to cadmium (0.2, 0.3, and 0.4 mg/L as CdCl2) through 4 consecutive generations revealed changes in demographic responses not only in survivorship variables but also in reproductive parameters. Long-term demographic responses varied differently, depending on the demographic trait and the concentration of heavy metal in the medium. With the exception of generation time, all life history traits were significantly and adversely influenced due to increase in Cd concentrations. The average life span of M macrocopa varied up to 40% depending on Cd level and the generation of exposure. The highest gross reproductive rates were recorded in controls, while the lowest (∼30% less) were recorded at the highest Cd level. Survival-weighted net reproductive rates were reduced by nearly 50% due to Cd toxicity. The rate of population increase per day of M macrocopa was also significantly affected (∼25%) by Cd as compared to controls. This cladoceran showed a dose-response to Cd toxicity with a significance in both magnitude and frequency of offspring production.

Temperature and age affect the life history characteristics and fatty acid profiles of Moina macrocopa (Cladocera).

Demographic responses and fatty acid profiles of Moina macrocopa were quantified under different temperature regimes (20°C, 25°C and 30°C and diurnally variable 20-30°C) and at fixed ration (10.65µgDWml(-1)) of Chlorella. Highest constant temperature (30°C) reduced the density of M. macrocopa. The cladocerans under the fluctuating temperature regime too had lower population growth (about 50% lower than that at constant 25°C). The survivorship of M. macrocopa was higher at 20°C than that at 25°C and 30°C or at variable temperature regime. Gross and net reproductive rates were higher at 25°C. At 20°C, neonates had the highest proportion (67%) of myristic, palmitic and stearic acids while the adults had the lowest (26%) proportion. For both adults and neonates, palmitoleic, linoleic and linolenic comprised of 15-35% of the total fatty acids. Higher percentage (19%) of linoleic acid was present in adults than neonates (7%). Adults had linolenic acid level which was 3-times higher than in neonates. Linoleic and linolenic fatty acids decreased with increasing temperature for neonates and adults from 20°C to 30°C. The demographic responses and fatty acid profiles of M. macrocopa were discussed in relation to level and mode of temperature exposure.

Somatic and population growth responses of Ceriodaphnia dubia and Daphnia pulex (Cladocera) to changes in food (Chlorella vulgaris) level and temperature.

We quantified the combined effects of three food levels (0.01 x 10(6), 0.1 x 10(6) and 1.0 x 10(6) cells ml(-1)) and three temperature levels (15, 20 and 25 degrees C) on the somatic and the clonal population growth of two cladocerans Ceriodaphnia dubia and Daphnia pulex for 24 to 42 days. The somatic growth data showed that both the cladoceran species began to increase their body size within 3 days and remained stable beyond a week. Food density had a significant effect on the body size of C. dubia while for D. pulex, food level and temperature as well as their interaction had significant effect on the body size. The population growth of both the cladoceran species was affected by temperature. At 15 degrees C, C. dubia showed little growth at the highest food density, while at low food level, there was some increase in the population abundances, especially after a long lag phase of about 2 weeks. At 15 degrees C and under the lowest tested food level, the population of D. pulex did not increase beyond the inoculation density. Optimal population growth of D. pulex was observed at intermediate temperature and at 1.0 x 10(6) cells ml(-1) of food level while for C. dubia 25 degrees C and the highest food level yielded highest growth. At low food level and low temperature, the rate of population increase (r) of C. dubia was much lower than that of D. pulex at comparable conditions. On the hand, at higher food levels and temperature regimes, the r of D. pulex was much higher than that of C.dubia. Regardless of the food levels and temperature, the r of C. dubia varied from 0.03 to 0.07 while that of D. pulex varied from 0.01 to 0.08 day(1).

Combined effects of exposure time and copper toxicity on the demography of Moina macrocopa (Crustacea: Cladocera).

Cohort life table experiments were conducted on M. macrocopa using copper at three nominal concentrations (as CuSO(4), 0.1, 0.2 and 0.4 mg L(- 1), in addition to controls) for different periods of exposure (3 to 24 h). Age-specific survivorship of M. macrocopa decreased in relation to age of the cohort, concentration and duration of exposure to copper. Age-specific life expectancy curves also decreased with increasing age of the cohort. However, at low copper levels and shorter exposure time, there was an increase in life expectancy when the cohort was about 10 day old. Fecundity (m(x)) was nearly regular in controls; however, at higher copper levels and longer duration of exposure, the offspring production was more oscillating. The offspring production completely ceased when continuously exposed to CuSO(4) at 0.4 mg L(- 1). Most of the measured demography variables significantly decreased with increasing concentration of Cu in the medium. The average lifespan and life expectancy at birth varied 2.9 to 9.6 and 2.4 to 9.1 days, respectively. Gross reproductive rate (GRR) varied from 31 to 89 offspring female(- 1) lifespan(- 1), while the survival-weighted net reproductive rates were nearly one-third of the GRR. Generation time of M. macrocopa varied from 5 to 7 days while the rate of population increase ranged from 0.36 to 0.84 per day. The results are discussed in relation to the sensitivity of M. macrocopa to copper toxicity and the necessity of amending the national water quality criteria in Mexico.

Prey (Brachionus calyciflorus and Brachionus havanaensis) exposed to heavy metals (Cu and Cd) for different durations and concentrations affect predator's (Asplanchna brightwellii) population growth.

In this work, we evaluated the combined effects of heavy metal concentration (CuSO(4) and CdCl(2) separately, at 0.1, 0.2 and 0.4 mg/L) and exposure time (6 and 24 h) on the population growth of the predatory rotifer Asplanchna brightwellii (predator) via its prey (Brachionus calyciflorus or Brachionus havanaensis). At low Cu concentration, B. calyciflorus stimulated the population growth of its predator as compared to controls. However, under higher Cd concentration and longer exposure time, B. calyciflorus caused lower growth of A. brightwellii. B. havanaensis previously exposed to Cu led to reduced growth of its predator, especially under high metal concentration. Regardless of the treatments, the population growth rates (r) of A. brightwellii varied from 0.11 +/- 0.02 to 0.45 +/- 0.04 d(- 1). The exposure time had significant influence on r of A. brightwellii via only the Cd-exposed prey B. havanaensis. However, regardless of the exposure time, B. calyciflorus exposed to Cu and B. havanaensis exposed to Cd stimulated the growth rate of the predator. In our study the predator was not directly exposed to heavy metals. Therefore, the toxicants acted in an indirect way on A. brightwellii, i. e., the predator's growth was affected through the ingestion of metal-contaminated prey.

Life table demography of Ceriodaphnia dubia (Cladocera) exposed to copper at different levels and periods.

We studied the demographic responses of Ceriodaphnia dubia exposed to copper at 3 different levels (0.1, 0.2 and 0.4 mg l(-1)) and at 4 exposure periods (3, 6, 12 and 24 hr) in addition to controls (without the heavy metal). The tested levels of Cu concentration and the chosen periods of exposure affected some demographic variables (average lifespan, gross and net reproductive rates and generation time). Depending on the heavy metal concentration and the period of exposure, the average lifespan of C. dubia varied from 18 to 24 day Net reproductive rates (NRR) ranged from 50 to 80 offspring per female per lifespan, while the rate of population increase (r) varied from 0.30 to 0.34 per day Though gross reproductive rates (especially at low and intermediate copper levels and shorter duration of exposure) showed significantly higher values than controls, both NRR and r were either unaffected or decreased. It is therefore necessary to regulate the release of untreated industrial effluents containing copper into freshwater ecosystems. Our study thus highlights the importance of including, not only toxicant concentrations but also exposure time, in ecotoxicological evaluations.

Effect of cadmium level and exposure time on the competition between zooplankton species Moina macrocopa (Cladocera) and Brachionus calyciflorus (Rotifera).

Competition among zooplankton is a natural phenomenon and often cladocerans are competitively superior to rotifers. However, anthropogenic factors including the release of industrial effluents, may influence this interaction. In this study, we evaluated the effect of cadmium (0.05 and 0.1 mg L(-1) as CdCl(2)) on competition between the cladoceran Moina macrocopa and the rotifer Brachionus calyciflorus. Since the release of industrial effluents is generally pulsed, we also exposed the test zooplankton species at different exposure periods (3, 6, 12 and 24 h) to the heavy metal. Regardless of exposure time and the presence of competing species, an increase in concentration of Cd resulted in decreased population growth of M. macrocopa and B. calyciflorus. Regardless of presence of the competing species and Cd concentration, an increase in exposure period resulted in decreased population growth rates of both the zooplankton species. In mixed cultures, in general, M. macrocopa outcompeted B. calyciflorus and completely eliminated it under conditions of high toxicant concentrations and longer exposure time.