Significance of environmentally realistic levels of selected contaminants to ecological performance of fish larvae: effects of atrazine, malathion, and methylmercury
This study uses a comprehensive approach to assess contaminants and modes of exposure effects on individuals and populations of two species of marine fish, specifically on the ecological performance (growth, behavior, survival potential, and resting respiration rate) of their larvae. Red drum (Sciaenops ocellatus) larvae at settlement size (7 mm total length) were given an acute exposure to atrazine (0, 40, and 80 µg l-1) or malathion (0, 1, and 10 µg l-1) in water for 4 days to evaluate the effects on ecologically critical traits. Atrazine significantly reduced growth rate and altered routine behavior (swimming speed, net-to-gross displacement ratio, and activity). Atrazine did not affect escape performance or resting respiration rate. Behavioral effects resulted in higher predicted prey encounter rates, but substantially elevated rates of energy utilization, which together suggest an increased risk of starvation. Atrazine effects on growth would prolong the larval period, which could reduce the juvenile population by up to 24 %. Malathion exposure at ecologically relevant concentrations did not impair any of the traits tested, suggesting that these levels may be safe for young fishes. However, recent increase in malathion use may elevate environmental levels above those tested here. In a different experimental approach larvae produced by adult Atlantic croaker (Micropogonias undulatus) fed a methylmercury-contaminated diet (0, 0.05, and 0.1 mg kg-1 d-1) for one month were screened for effects on routine and escape behaviors. Four developmental stages were studied: (1) end of yolk absorption (yolk), (2) end of oil absorption (oil), (3) 4 days and (4) 11 days after oil absorption (oil+4 and oil+11). MeHg levels in the eggs (0.04 to 4.6 ng g-1) induced a range of stage- and concentration-dependent effects that were more frequent during yolk absorption, suggesting physiological, rather than developmental, effects. Computer simulations applied to predict the ecological relevance of the observed behavioral effects suggested that methylmercury-exposed larvae would have lower survival during the planktonic stage (< 12 mm) compared to unexposed larvae (< 96 % reduction). It is demonstrated here that environmentally realistic pollution may substantially reduce fish larvae survival and compromise recruitment to juvenile populations.