Environmental levels of atrazine and its degradation products impair survival skills and growth of red drum larvae

Red drum larvae (Sciaenops ocellatus) were exposed to environmentally realistic and sublethal levels of the herbicide atrazine (2-chloro-4-ethylamin-6-isopropylamino-S-triazine) to evaluate its effects on ecologically critical traits: growth, behavior, survival potential, and resting respiration rate. Settlement size larvae (7 mm total length) were given an acute exposure of atrazine at 0, 40, and 80 μg l−1 for 4 days. Tests of 96 h survival confirmed that these naturally occurring concentrations were sublethal for red drum larvae. Growth, routine swimming, antipredator responses to artificial and actual predators, and resting respiration rate were monitored 1 and 3 days after onset of exposure. Atrazine exposure significantly reduced growth rate. Atrazine-exposed larvae also exhibited significantly higher routine swimming speeds, swam in more convoluted paths, and were hyperactive. Responses to artificial and actual predators were not affected by atrazine exposure nor were resting respiration rates. The higher rate of travel (86% higher in atrazine-treated larvae) resulted in higher predicted encounter rates with prey (up to 71%) and slow moving predators (up to 63%). However, hyperactivity and faster active swimming speeds of exposed larvae indicated that naturally occurring sublethal levels of atrazine will result in an elevated rate of energy utilization (doubling the total metabolic rate), which is likely to increase the risk of death by starvation. Moreover, atrazine effects on growth will prolong the larval period, which could reduce the juvenile population by as much as 24%. We conclude that environmentally realistic levels of atrazine induce behavioral and physiological effects on fish larvae that would compromise their survival expectations.