An investigation of enhanced mercury bioaccumulation in fish from offshore feeding.

We investigated the dietary pathways of mercury transfer in the food web of Morency Lake (Canada) to determine the influence of carbon source and habitat use on mercury bioaccumulation in fish. Whole-body concentrations of methylmercury (MeHg) were significantly different in four fish species (white sucker, brown bullhead, pumpkinseed and smallmouth bass) and increased with both trophic position and greater feeding on offshore (versus littoral) carbon. An examination of fish gut contents and the depth distribution of invertebrates in Morency Lake showed that smallmouth bass and brown bullhead were supplementing their littoral diet with the consumption of either opossum shrimp (Mysis diluviana) or profundal amphipods in offshore waters. The zooplanktivore Mysis had significantly higher MeHg concentrations than zooplankton and benthic invertebrates, and it was an elevated source of MeHg to smallmouth bass. In contrast, profundal amphipods consumed by brown bullhead did not have higher MeHg concentrations than littoral amphipods. Instead, partitioning of benthic invertebrate resources likely explains the greater MeHg bioaccumulation in brown bullhead, associated with offshore feeding of amphipods. White sucker and brown bullhead had a similar trophic position but white sucker consumed more chironomids, which had one-third the MeHg concentration of amphipods. Our findings suggest that offshore feeding in a lake can affect fish MeHg bioaccumulation via two different processes: (1) the consumption of MeHg-enriched pelagic prey, or (2) resource partitioning of benthic primary consumers with different MeHg concentrations. These observations on the mechanisms of habitat-specific bioaccumulation highlight the complexity of MeHg transfer through lake food webs.

Spina bifida in a pre-Columbian Cuban population: A paleoepidemiological study of genetic and dietary risk factors.

A holistic approach is necessary to investigate health in archeological populations. Molecular techniques, particularly multiplex PCR and SNaPshot minisequencing, can be combined with paleopathology and dietary analysis (stable isotope, starch, zooarchaeological analyses) to understand aspects of population health. This article demonstrates how spina bifida, a multi-factorial disease characterized by the midline failure to complete vertebral neural arch formation, can be investigated holistically. Based on skeletal evidence, this disease was prevalent in a pre-Columbian Cuban population from the archeological site of Canimar Abajo (3000-1250 BP). Molecular paleopathological techniques were employed to examine disease potential in this preliminary study, examining 18 individuals (including two individuals with evidence of mild spina bifida, and 16 without such evidence) for four single nucleotide polymorphisms and one insertion sequence associated with spina bifida. The combined effect of these polymorphisms, as well as dietary factors, determines the risk of the population for spina bifida, and these factors united to create the observed high disease prevalence. We demonstrate how molecular paleopathology, corroborated by dietary analyses, can be used within a paleoepidemiological framework to understand population health and disease.

Metamorphosis in chironomids, more than mercury supply, controls methylmercury transfer to fish in High Arctic lakes.

Lake-dwelling Arctic char (Salvelinus alpinus) are monitored internationally as a sentinel species for effects of atmospheric mercury deposition on Arctic fresh waters. We investigated the control of mercury supply and biological processes on the methylmercury (MeHg) content of their main food, aquatic chironomids, in 22 lakes and ponds in the Canadian High Arctic. Total mercury (THg) concentrations in sediment (corrected for organic matter content) increased with drainage basin size, suggesting a gradient in mercury loading among study sites. MeHg concentrations in sediment and water were low and relatively uniform along this THg supply gradient suggesting MeHg production in High Arctic lakes is weakly coupled to inorganic mercury supply. Metamorphosis was a key biological process that concentrated MeHg in adult chironomids 1.7-2.9 times more than in immature stages. Drainage basin size, environmental mercury levels, and habitat characteristics were also significant factors but they explained less variation in chironomid MeHg concentration than their degree of maturity. Chironomid larvae, pupae, and adults are distinct mercury sources for fish, and we provide evidence from nitrogen stable isotopes and published feeding studies that suggest differential consumption of these stages may affect MeHg uptake by Arctic char. We conclude that biological and food web processes have a greater impact on MeHg transfer to fish than atmospheric mercury deposition in High Arctic lakes.