Responses of Blueback Herring Eggs and Larvae to Pulses of Acid and Aluminum

Abstract

We measured the sensitivity of eggs and yolk-sac larvae of blueback herring Alosa aestivalis to acid and aluminum pulses in moderately soft fresh water (23–25 mg/L, hardness as CaCO3) during 96-h experiments in the laboratory. Over a 3-h period, pH was reduced from 7.4–7.7 to 5.5–5.6, coincident with an increase in aluminum from 0 to 0.10, 0.15, 0.20, or 0.25 mg/L. These pH-aluminum conditions were maintained for five single-pulse durations (0.5, 4, 8, 12, 24 h) and then gradually returned to control conditions within 8–10 h. Relatively mature embryos (20–24 h postfertilization, early tail-bud stage) were more tolerant than larvae to all treatments. Eggs exposed to a 24-h pulse of pH 5.5–5.6 and 0.20 mg/L total aluminum (predicted total monomeric aluminum, 0.09 mg/L) experienced the highest mortality observed for this life stage, 48%. Larvae tolerated single pulses of pH 5.5–5.6 (without aluminum) for up to 12 h, but mortality doubled (25% to 49%) when pulse duration doubled (12 h to 24 h). Pulses of 0.10–0.15 mg/L total aluminum (predicted total monomeric aluminum, 0.05–0.07 mg/L) coincident with acid pulses of pH 5.5–5.6 increased larval mortality from 19% after a 4-h pulse to 66% after an 8-h pulse to 98 and 100% after 12- and 24-h pulses, respectively. Our results suggest that acidic episodes (or spates) and associated mobilization of inorganic aluminum in coastal plain tributaries of Chesapeake Bay during spring rain storms may be an important source of early life stage mortality for blueback herring populations that spawn in these poorly buffered habitats.