title: Effects of mercury on the life table demography of the rotifer Brachionus calyciflorus Pallas (Rotifera).
abstract: Mercury is highly toxic to a variety of aquatic organisms including zooplankton. The functioning of freshwater ecosystems can be altered if rotifers, being a natural food link between phytoplankton and fish larvae, are contaminated by mercuric compounds. In order to detect age-specific responses of the rotifer Brachionus calyciflorus to mercury toxicity (5 nominal concentrations as chloride viz. 0, 0.000625, 0.00125, 0.0025 and 0.005 mg l(-1)), we used the standard life table method at two different food (Chlorella vulgaris) levels (0.5 x 10(6) and 1.5 x 10(6) cells ml(-1)). Data indicated that increase in mercury concentration had an increasingly intense negative effect on many of the life history variables, while at higher food levels, its impact was less. A nearly rectangular survivorship pattern was obtained in controls, especially at higher food levels. This trend gradually changed to a steep fall as the concentration of the heavy metal in the medium increased from 0 to 0.005 mg l(-1). At any given food density, increase in the mercury concentration resulted in decreased age-specific reproduction. A maximum of 3.5 offspring female(-1) was observed in controls at higher food density. The average lifespan varied from 6 to 8 days at low food level, depending on the heavy metal concentration in the medium. The corresponding values at high food level varied from 8 to 12 days. Regardless of mercury concentration in the medium, gross and net reproductive values varied from 10 to 33 and 4 to 19 offspring female(-1). The longest generation time (about 9 days) of B. calyciflorus was obtained at 1.5 x 10(6) cells ml(-1) food density in control, while the shortest was 5 days at low food level and high (0.005 mg l(-1)) mercury concentration in the medium. Depending on the food level and heavy metal concentration in the medium, the rate of population growth (r) varied from 0.32 to 0.62 d(-1). In general, higher food level resulted in higher r. Except generation time, all other derived variables were significantly influenced by food level and the heavy metal concentration in the medium.
authors.affiliation: Laboratory of Aquatic Zoology, Edificio UMF, National Autonomous University of Mexico, Campus Iztacala, Tlalnepantla, State of Mexico, Mexico.
authors.forename: Teresa
authors.initials: T
authors.lastname: Ramírez-Pérez
authors.forename: S S S
authors.initials: SS
authors.lastname: Sarma
authors.forename: S
authors.initials: S
authors.lastname: Nandini
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002708:Chlorella / Q000502:physiology; D005260:Female; D007928:Lethal Dose 50; D015993:Life Tables; D008628:Mercury / Q000633:toxicity*; D011156:Population Density; D011158:Population Growth; D012098:Reproduction / Q000187:drug effects*; D012403:Rotifera / Q000187:drug effects* / Q000254:growth & development; D013997:Time Factors; D014874:Water Pollutants, Chemical / Q000633:toxicity
chemical_list: D014874:Water Pollutants, Chemical; D008628:Mercury