Bioenergetic, reproductive, and population-level effects of dissolved copper and cadmium on the grass shrimp, Palaemonetes pugio
Rowe, Christopher L
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The grass shrimp, Palaemonetes pugio, was exposed to dissolved copper or cadmium in a series of laboratory experiments to determine effects on bioenergetics, reproduction, and population growth. In 14-day exposures, adults were exposed to either copper or cadmium to quantify bioenergetic effects. Both metals caused a decline in oxygen consumption (lowest observed effects concentrations [LOECs] = 7.5 μg Cu sup 2+/L and 6.6 μg Cd sup 2+L) and growth rate (LOECs = 27 μg Cu sup 2+/L and 6.2 μg Cd sup 2+/L). Effects of copper on growth were more severe than those of cadmium, resulting in weight loss during the exposure. Reductions in oxygen consumption and growth, in combination with declines in reproduction observed in longer exposures, suggest that both copper and cadmium reduce energy allocation to respiration and production pathways. In eight-month exposures, <em>P. pugio</em> were exposed to either copper or cadmium for a full life cycle, allowing larvae to attain maturation and reproduce. While survival was little affected by exposure to cadmium, brood size and the percentage of ovigerous females were significantly reduced (LOECs = 1.5 and 2.5 μg Cd sup 2+/L, respectively). Population growth of P. pugio exposed to cadmium was projected using a stage-based matrix model and a z-transformed life cycle graph analysis. Both models projected a decrease in population growth rate (LOEC = 1.5 μg Cd sup 2+/L), although population growth remained positive. Decomposition analysis indicated that cadmium-induced declines in population growth could be attributed mainly to contributions from reproductive effects. In the eight-month exposure to copper, no lethal effects on larvae, juveniles, or adults were observed, but larval development was significantly delayed (LOEC = 9 μg Cu sup 2+/L). Upon reaching maturation, females exposed to copper were able to produce embryos, but the embryos did not hatch, precluding completion of the life cycle (LOEC = 9 μg Cu sup 2+/L). The results from subsequent experiments, which further examined reproductive effects, suggested that copper may inhibit larval recruitment via a combination of effects on hatching success, parental bioenergetics, and processes before or during spawning and/or fertilization. In conclusion, both copper and cadmium may have negative impacts on the sustainability of natural populations of P. pugio in contaminated habitats.