Chronic exposure of Leptocheirus plumulosus to Baltimore Harbor sediment: bioenergetic and population-level effects

We investigated the long-term effects of contaminants in sediment from Baltimore Harbor, MD, USA, on a burrowing amphipod (Leptocheirus plumulosus) via a full life-cycle laboratory exposure. Contaminants in the Baltimore Harbor sediment included PAHs (10,800 ng/g), PCBs (152 ng/g), and heavy metals (including As, Cd, Cu, Pb, Hg, Ni, and Zn). Exposures were initiated with neonate amphipods, placed in microcosms containing either contaminated or reference sediment, and were maintained for 42 days, allowing ample time for the initial cohort to mature and reproduce. At the end of the exposure period, the populations of amphipods were surveyed to ascertain the number and size of amphipods in each size class (neonate, juvenile, and adult), and bioenergetic measurements were performed on adults, including metabolic rate, lipid content, and fecundity. Contaminated sediment from Baltimore Harbor caused lower growth and reproductive rates; in Baltimore Harbor sediment, the average dry weight of amphipod offspring in each size class was significantly lower and there were less than one-third as many individuals in each size class, compared to reference sediment. By the end of the exposure, the total amphipod biomass in Baltimore Harbor sediment was less than one quarter of that in reference sediment. On average, gravid females in reference sediment produced at least twice as many viable offspring as those in contaminated sediment. Adult male amphipods in Baltimore Harbor sediment possessed significantly lower lipid concentrations. Lipid content in neonates also appeared to be negatively affected by parental exposure to contaminants. Metabolic rate was elevated in adult amphipods exposed to Baltimore Harbor sediment. Overall, the results suggest that contaminated sediment conditions in the urban estuary may chronically affect L. plumulosus by diverting energy from production to maintenance pathways, resulting in slower growth and reduced fecundity, and ultimately leading to retarded population growth rates. The results of this study reinforce the need for long-term toxicological exposures to reveal chronic effects.