Sss. Sarma et al., Combined effects of food concentration and the herbicide 2,4-dichlorophenoxyacetic acid on the population dynamics of Brachionus patulus (Rotifera), ECOTOXICOL, 10(2), 2001, pp. 91-99
Herbicides are important in crop protection and management. A number of the
m including 2,4-D (2,4-dichlorophenoxyacetic acid), however, may reach wate
r bodies and eventually affect the non-target organisms such as rotifers. I
n the present work, we studied the influence of 6 concentrations viz. 0 (co
ntrol), 100, 200, 300, 400 and 500 mg l(-1) of 2,4-D on the population grow
th of the rotifer Brachionus patulus under two algal (Chlorella) food level
s (0.5 x 10(6) and 1.5 x 10(6) cells ml(-1)). Regardless of herbicide conce
ntration, the population growth of B. patulus was dependent on the algal fo
od levels, in that an increase in algal food level supported a better popul
ation growth. Similarly at any Chlorella density, the herbicide had a negat
ive influence on the population growth of B. patulus. Herbicide level of 50
0 mg l(-1) inhibited population growth of B. patulus beyond 5 days. Rotifer
s grown under low food density and high herbicide concentration (300 mg l(-
1) or above) were completely eliminated after day 15. The rate of populatio
n increase (r) (mean +/- standard error) in the controls varied from 0.46 /- 0.002 and 0.55 +/- 0.004 under 0.5 X 10(6) and 1.5 X 10(6) cells ml(-1)
of Chlorella, respectively. The r values became negative under both, low an
d high food levels, at or beyond 300 mg l(-1) of 2,4-D. The maximal populat
ion abundance (ind. ml(-1)) in controls varied from 294 +/- 9 to 503 +/- 21
under low and high food levels of Chlorella, respectively. The role of alg
ae in mitigating adverse effects of high herbicide concentrations to rotife
rs has been discussed.