Seabirds as monitors of mercury in the marine environment

Abstract

The oceans play a major role in global cycling of mercury and widespread contamination of marine ecosystems has been demonstrated in recent years. Monitoring mercury in the marine environment is a priority and biomonitoring has featured prominently in this respect. Seabirds, as top predators, present high mercury levels due to food chain amplification and thus will reflect slight variations in environmental mercury and its hazards to humans better than do most invertebrates and cold blood vertebrates. There is experimental evidence that levels of mercury in seabirds show a dose-response relationship, so that increased contamination of the environment causes a corresponding increase in the level in birds. This coupled with current knowledge on the dynamics of mercury in birds gives a good basis for the use of seabird as monitors of mercury. Internal tissues, blood, eggs, feathers and chicks have been used as monitoring units. Feathers are the most attractive amongst them. They are both chemically and physically stable, accumulate higher mercury levels than other tissues and their sampling is non-destructive. However, it is essential to sample a consistent feather area from all birds to minimise the effects of moult and body feathers are the most adequate. Feathers from birds in museum collections offer a great potential for the study of synoptic geographical and historical of changes in mercury levels on a global scale with large sample sizes. For example, studies with time series of feather samples from seabirds provide evidence of a 3-fold increase of mercury contamination in the marine ecosystem of North-eastern Atlantic over the last 100 years and little increase in mercury contamination in the Southern hemisphere during the same period.