Impacts of multiple stressors on growth and metabolic rate of Malaclemys terrapin

Coastal species encounter numerous physiological stressors ranging from daily fluctuations in salinity and temperature to anthropogenic contaminants, yet the effects of such stressor combinations on aquatic organisms remain largely unknown. Exposure to environmental contaminants, such as polychlorinated biphenyls (PCBs), can disrupt physiological processes, and while physiological responses to salinity change are well understood, the combined effects of salinity change and contaminants on these processes are unknown. Marine and brackish water turtles are often simultaneously exposed to both stressors. We exposed male, eight-month-old diamondback terrapins to one of four salinity treatments (0, 10, 20, and 30 parts per thousand) in the presence and absence of the anthropogenic stressor 3,3',4,4',5-pentachlorobiphenyl (PCB 126, 20 microg/g via intraperitoneal injection) and monitored growth (carapace length and mass) and metabolic rate for six months. Exposure to PCB 126 significantly reduced growth (p < 0.0001), lowered standard metabolic rates (SMRs; p < 0.0001), and altered respiratory pattern (p < 0.0001). Salinity stress reduced growth (p < 0.0001) and altered the respiratory pattern (p < 0.0001) but had no overall effect on metabolic rate (p = 0.33). No interactive effects of PCBs and salinity were seen on either growth or metabolic rate. Our data indicate terrapins may be able to cope with some effects of salinity change through physiological adjustments but are less able to cope with PCBs. We show that PCB 126 disrupts the ecophysiological mechanisms that affect life history traits and thus ultimately could alter population structure and dynamics. The present study enriches our understanding of the environmental toxicology of reptiles and aids in the interpretation of health conditions documented in field-collected turtles contaminated with PCBs.