Ecological factors differentially affect mercury levels in two species of sympatric marine birds of the North Pacific

• Published in: The Science of the total environment 2011-03, Vol.409 (7), p.1328-1335
• Main Authors: Hipfner, J.M., Hobson, K.A., Elliott, J.E.
• Format: Article
• Language: English
• Subjects: adults; Age Factors; age structure; Animal, plant and microbial ecology; Animals; Applied ecology; Auklets; Aves; Biological and medical sciences; blood; Breeding stage; Carbon Isotopes - blood; Cerorhinca monocerata; Charadriiformes - blood; Crustacea; Ecosystem; Ecotoxicology, biological effects of pollution; Effects of pollution and side effects of pesticides on vertebrates; Environmental Monitoring; fish; Food Chain; Fundamental and applied biological sciences. Psychology; Marine; Mercury; Mercury - blood; Nitrogen Isotopes - blood; Pacific Ocean; predators; progeny; Ptychoramphus aleuticus; Rhinoceros; Seabirds; Stable isotopes; sympatric species; Triangle Island; Water Pollutants, Chemical - blood
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2010.12.022

In 2003 and 2004, we measured mercury concentrations and δ 15N and δ 13C values in the whole blood of adults of two species of seabirds, Cassin's auklet ( Ptychoramphus aleuticus) and rhinoceros auklet ( Cerorhinca monocerata), during their prelaying, incubation, and provisioning periods. We also collected whole blood from the offspring of both seabirds. Among prey items, δ 15N values were higher in fish than in crustaceans, while δ 13C did not vary systematically between prey types. Mercury concentrations in prey showed little relationship with either stable isotope. In the zooplanktivorous Cassin's auklet, year, reproductive stage, and δ 15N and δ 13C stable isotope values explained only 14% of the variation in mercury concentrations in adult blood, and none of these variables had a statistically significant effect. In contrast, these same variables explained 41% of the variation in mercury levels in the more piscivorous rhinoceros auklet, and all but δ 15N values had statistically significant effects. Mercury concentrations in adult rhinoceros auklets were higher in 2003 than in 2004; higher prior to laying than during the incubation or provisioning periods; and increased with δ 13C values — but in just one of two years. In both species, mercury concentrations were substantially higher in adults than in nestlings. Our results accord with previous studies in showing that mercury concentrations can vary among years, species and age classes, while the marked variation with reproductive stage is noteworthy because it is so rarely considered. Our results may help to explain the disparate conclusions of previous studies: while many factors influence mercury concentrations in marine predators, they apparently do so in a manner that defies easy characterization. We believe that there is a need for more studies that consider a range of physiological, ecological and behavioral factors that might affect mercury burdens in marine predators. ► We measured mercury levels in two seabirds across two entire breeding seasons. ► Levels in rhinoceros auklets varied among years and foraging habitats, and peaked prior to laying. ► Levels in Cassin’s auklets were much more constant. ► Lack of consistency within and between species accords with disparate results of earlier studies.