Nutrient And Contaminant Dynamics In The Marine Food Web Of Kotzebue Sound (Alaska)

Abstract

The objectives of these studies were to document nutrient and contaminant concentrations in upper trophic level organisms of the Kotzeue, Alaska marine food web; address associated risks and benefits to human consumers of these species; understand the drivers of nutrient and contaminant patterns and concentrations; and test the limitations of chemical feeding ecology tools used to trace nutrient and contaminant pathways within this food web. Tissues of subsistence harvested animals were analyzed for nutrients, contaminants and stable isotopes (delta13C and delta15N). Foods derived from sheefish (Stenodus leucicthys) and spotted seal (Phoca largha) provide numerous essential nutrients, with limited risk from contaminant exposure. Food processing altered nutrient and contaminant concentrations and stable isotope ratios, warranting the evaluation of foods as they are ultimately consumed when determining the risks and benefits of traditional diets. delta13C and delta15N, common chemical tracers of feeding ecology and contaminant pathways in food webs, varied widely by tissue type. delta15N and mercury did not differ consistently among seal tissues. Consequently, when utilizing stable isotopes as tracers of feeding ecology and mercury exposure, the specific tissue consumed and the processed state of the tissue should be considered. Bioaccumulation patterns differed between sheefish and spotted seals in relation to their respiratory physiology and persistent organic pollutant (POP) partitioning behavior between lipids and the respiratory medium (i.e., air versus water). Certain POPs that do not bioaccumulate in fish due to rapid excretion across the gills into surrounding waters (low KOW) do bioaccumulate in seals if not efficiently eliminated via the lungs to the air (high K OA). Thus, KOW alone cannot predict bioaccumulation in mammals. Regulatory guidelines must incorporate KOA into chemical risk-assessments for air-breathing species, including humans and marine mammals. Ringed ( Phoca hispida), spotted and bearded (Erignathus barbatus ) seals had distinct blubber fatty acid (FA) signatures. Blubber of ringed and spotted seals exhibited significant stratification relative to both FA degree of unsaturation and carbon chain length. FA stratification appears largely driven by the steep temperature gradient of blubber, except in the case of polyunsaturated FA (PUFA) which may be maintained in the inner blubber for rapid mobilization to meet physiological requirements.