Sensitivity of early life stages of blueback herring to moderate acidity and aluminum in soft freshwater
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The sensitivity of the blueback herringAlosa aestivalis to acidity and aluminum (AI) in reconstituted, soft freshwater (23–25 mg I−1 hardness as CaCO3) was investigated in a continuous exposure laboratory study. Mature (20–24 h postfertilization) embryos were more tolerant than 1- to 5-day-old yolk-sac larvae. Significant mortality of embryos occurred only when pH was 5.0 and the total Al concentration was 0.42 mg I−1 (predicted MIBK-extracted total monomeric AI=0.34 mgI−1). Moderate acidity dramatically decreased the survival of yolksac larvae. Mean mortality was 99% in pH 5.0 and 89% in pH 5.7 compared to 38% in pH 6.5 and 16% in pH 7.8 without AI. The toxicity of AI to yolk-sac larvae was pH- and dose-dependent. Total AI concentrations up to 0.34 mg l−1 (predicted total monomeric AI up to 0.21 mg l−1) were not toxic at pH 6.5 and 7.8. At pH 5.0 and 5.7, AI increased the rate at which yolk-sac larvae died during a 96-h exposure (i.e., time to 50% mortality decreased with increasing AI). Continuous exposure to a predicted total monomeric AI level of only 0.03 mg I−1 at pH 5.0 killed all yolk-sac larvae in <24 hours. The mechanisms of acid and AI toxicity were apparently physiological and not associated with extensive cellular damage. Acidification events measured in Chesapeake Bay tributaries may reduce survival of blueback herring yolk-sac larvae and embryos exposed to those events.