Chemical and biological pollution contribute to the immunological profiles of free-ranging harbor seals

Abstract

Polychlorinated biphenyls and other persistent organic pollutants have been associated with immunotoxicity and outbreaks of (infectious) disease in marine mammals by rendering them vulnerable to infection by pathogens such as viruses and bacteria. In an immunotoxicological study of free-ranging harbor seals (Phoca vitulina), we obtained samples of blood and blubber from seal pups that were live-captured from two remote and two near-urban sites in British Columbia, Canada, and Washington state, USA. Using these samples, we quantified hematology, innate immune function, adaptive immune function, and polychlorinated biphenyl accumulation. While controlling for confounding factors (age, sex, and condition), univariate correlations between phagocytosis (r2 = 0.30, p = 0.002), respiratory burst (r2 =0.45, p= 0.000), T-lymphocyte function (r2 = 0.16, p = 0.028), lymphocyte signaling (r2 = 0.17, p = 0.025), and lymphocyte counts (r2 = 0.29, p = 0.002), and polychlorinated biphenyl concentrations suggested chemical-associated immunotoxicity. Principal component analysis of immunological endpoints provided additional evidence of immunotoxic effects in seals. However, principal component analysis also identified a noncontaminant-related factor by distinguishing between seals inhabiting urban versus remote sites, with results being consistent with increased pathogen exposure. Elevated fecal coliform concentrations in water, and observations of terrestrial spill-over pathogens in local seals, further support the notion of biological pollution at these sites. Although our study highlights the role that environmental contaminants might play in rendering marine mammal populations vulnerable to disease through immunotoxicity, it also suggests that biological pollution represents an emerging conservation concern.

Emerging infectious diseases in cetaceans worldwide and the possible role of environmental stressors

“…Biological pollution is an emerging issue, with the findings of terrestrial pathogens in marine mammals, of a significant increased fecal coliform count in harbour seals living near urban developments and of cutaneous disorders of miscelleanous aetiology in coastal odontocetes (Mos et al 2006, Van Bressem et al 2007b, Miller et al 2008. Climate changes can increase water temperatures, modify the distribution of vectors and reservoir species, change pathogen and host interaction dynamics and alter pathogen transmission cycles (Greer et al 2008).…”

Use of glacial and terrestrial habitats by harbor seals in Glacier Bay, Alaska: costs and benefits

“…Ross 2000, Boyd & Murray 2001, Mos et al 2006. Among pinnipeds, harbor seals have the broadest distribution (from ap proximately 30°t o 80°N in the eastern Atlantic region and from 28° to 62°N in the eastern Pacific region) and occur in diverse habitats (Perrin et al 2002).…”

The marine mammal microbiome: current knowledge and future directions

“…For marine mammals, susceptibility to pathogens may be particularly elevated due to anthropogenic stressors such as depleted food resources, habitat degradation and chemical or sound exposure [12][13][14][15] . Additionally, succession events occurring after an initial bacterial infection may lead to dysbiosis, and alterations in the host's microbiome may be a better predictor of disease progression than following the presence of individual pathogenic agents 16 .…”