Effects of mercury on the life table demography of the rotifer Brachionus calyciflorus Pallas (Rotifera)
Ramírez-Pérez, T.; Sarma, S.S.S.; Nandini, S.
Ecotoxicology 13(6): 535-544
ISSN/ISBN: 0963-9292 PMID: 15526859 Accession: 034824518
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 106 and 1.5 x 106 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 106 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.