Factors impacting contaminant body burdens and contaminant effects at different trophic levels in an estuarine ecosystem



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Organic contaminants continue to enter coastal ecosystems, creating stress for animals that inhabit these areas. A variety of factors such as land use, climate, and habitat usage have the potential to impact the accumulation and effects of these organic chemicals. At the same time, the role of these factors in modifying accumulation or contaminant effects at one trophic level can have indirect impacts on higher trophic levels. One example of a negatively impacted coastal ecosystem where land use and climate impact the effects of organic contaminants is the Charleston Harbor estuarine area in Charleston, South Carolina. The objective of this set of studies was to examine the impacts of shifts in land use and climate on contaminant uptake in the Charleston Harbor ecosystem. To better understand these effects at different trophic levels, the bottlenose dolphin was selected as a representative sentinel species. Atlantic croaker was selected as a representative dolphin prey species.
The first objective was to use GIS modeling techniques to investigate the relationship between environmental factors and body burdens of organic contaminants in bottlenose dolphins and in dolphin prey fish (e.g. Atlantic croaker). The second objective was to focus on the effects of changing temperatures on uptake of triclosan (a poorly understood antimicrobial chemical with increasing environmental concentrations) in Atlantic croaker in a lab environment as well as to study effects of this chemical on croaker physiology using a series of reflex action mortality predictors (RAMP). The final objective was to explore the effects of triclosan on anti-predator behavior in Atlantic croaker, specifically whether increased exposure would make Atlantic croaker more vulnerable to predation by impacting the strategies used by fish to escape a simulated predator or burst swimming performance. The two triclosan studies consisted of 64 fish randomly assigned to one of four treatment groups which represented a combination of two temperatures and triclosan exposure or no triclosan exposure. The GIS study found that the most important variables in predicting dolphin contaminant loads included a combination of land use characteristics, prey fish characteristics, and characteristics of the individual dolphin, demonstrating the importance of looking at various factors simultaneously. Additionally, some variables were important in fish models but not dolphin models, meaning they could indirectly impact dolphin contaminant body burdens. This study also found that preferential predation on highly contaminated fish may play a role in dolphin contaminant concentrations. The lab studies of triclosan accumulation and effects in Atlantic croaker found that exposure to triclosan at a higher water temperature led to significantly higher accumulation of triclosan than exposure at a lower temperature. Exposure to triclosan, but not changes in water temperature, significantly negatively impacted fish reflexes, specifically resulting in the loss of the dorsal spine reflex. This reflex did not return in any fish during a 5 week reflex recovery trial. The impact of triclosan on the dorsal spine reflex may provide insight into the other sublethal effects of triclosan as well as potential impacts on social patterning in these fish. Triclosan exposure also significantly impacted the strategies employed by croaker to escape a simulated predator, with triclosan exposed fish spending more time stationary than their non-exposed counterparts. There was no effect of water temperature on the strategies used. All four groups were significantly different from one another in terms of swimming performance. The most important factor discriminating between both low and high water temperature as well as control and triclosan groups was total food consumed. Actual triclosan body burden only had a significant effect on the ninth principle component which represents only 0.07% of the total variance in the data. Notably, this was the only principle component where the number of bursts loads strongly. The effects of water temperature on triclosan accumulation as well as the effects of triclosan exposure on anti-predator behavior may lead to differential predation for croaker and have impacts on bioaccumulation in higher trophic level species that consume croaker.



Ecotoxicology, Contaminants, Bottlenose dolphins, Atlantic croaker, Dichlorodiphenyltrichloroethane (DDT), Polybrominated diphenyl ethers (PBDEs), Polychlorinated biphenyls (PCBs), Triclosan, Geographic information systems (GIS), Anti-predator behavior, Model, Physiology, Land use, Climate, South Carolina, Marine