Molecular biomarkers as tools to assess the health of top predators in the Baltic Sea ecosystem: Using threatened seal species as sentinels.

Supervisors: Kristina Lehnert, Ursula Siebert (University of Veterinary Medicine Hannover).
The Baltic Sea located in Northern Europe is a heavily impacted brackish marine environment exposed to several anthropogenic stressors including acoustic noise and environmental contaminants due to the large number of people living in its catchment area. The resident seal species ringed seals (Pusa hispida), grey seals (Halichoerus grypys) and harbour seals (Phoca vitulina), are continuously exposed to these environmental contaminants through feeding, and because they are long-lived top predators, they accumulate a lot of these contaminants in their tissues over time. Minimally invasive molecular biomarkers which show early onset effects of the exposure to these contaminants are especially important because of the ethical and juridical constraints in sampling and studying free ranging wildlife. With the aid of quantitative real-time polymerase chain reactions (qPCR), this study measured for the first time the mRNA transcript levels of xenobiotic (ARNT and PPARα), endocrine disruption (TRα, TSHβ, ESR1 and RARα) and acute phase protein (HSP70) biomarkers in the blood of thirteen ringed seals, one grey seal and one harbour seal sampled across the Baltic Sea. mRNA transcription levels were then correlated with mercury concentrations in the liver and muscle tissues of the ringed seals. Species-specific differences were observed in mRNA transcription levels of ARNT, PPARα and TSHβ, indicating species-specific physiological responses in these species. There were no statistically significant differences of mRNA transcription levels of the biomarkers between the ringed seal sexes, but higher levels recorded in the males were probably a result of low pollutant burden in the females caused by transfer to their offspring. Differences between the ringed seals age classes is assumed to be linked to their varied prey differences. Post-mortem artefacts caused by RNA degradation were observed in mRNA expression levels of dead stranded seals that were found on the beach. The biomarkers showed no correlations with the mercury concentrations in the liver and muscle tissue of the ringed seals. These results reflect that minimally invasive biomarkers are sensitive tools to evaluate health, pollutant exposure and immune functions and can be used to monitor live populations and inform conservation decisions.