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Pollution and sea birds

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South American tern © Michael Schepard

Like marine mammals, sea birds are in all marine ecosystems at the top (or very near the top) of the food chain. As such, they are particularly sensitive towards biomagnifying substances. The best known biomagnifying contaminants are organochlorine pesticides (like DDTs), polychlorinated biphenyls (PCBs) and methylmercury.

Organoclorine compounds

Since the 1960s it is known that organochlorine pesticides can cause mortality, reduced fertility and eggshell thinning in terrestrial predatory birds. Effects of organochlorine pesticides have also been detected in sea birds. In 1965, the population of the Dutch Sandwich Tern colony on the island of Griend declined, from 20.000 to 650 individuals, due to pesticide effluents form a chemical factory. An estimated 50.000 - 100.000 common guillemots died in the Irish Sea in 1969 with liver and kidney lesions similar to those caused by PCBs. However, it couldn't be proven that the guillemots indeed died by PCB poisoning[1]. It was even suggested that the PCB contamination was only contributory and not the primary cause of the mass death[2]. DDTs have caused eggshell thinning during the 1960s and 1970s in pelicans and petrels. The eggs became so thin that when the birds sat on them for incubation, the eggs broke. This obliviously caused severe population declines in the affected species[2].

Methylmercury

Unlike terrestrial birds, some sea birds can typically accumulate large amounts of mercury without negative effects. High values, which would be lethal for terrestrial birds were measured in the feathers of albatrosses, although they showed no signs of damage. Like marine mammals, some sea birds might be able to transform methylmercury in less toxic inorganic mercury. Furthermore the birds transport methylmercury to their growing feathers. In some sea birds, up to 93% of the total mercury is stored in the feathers, where they cause no harm[1].

Below you can find some links to Belgian case studies on ecotoxicology in sea birds.

Case studies

Case study 1: The relation between pollutants and disease in guillemots [3]

Case study 2: Possible causes for breading failure in common terns[4]


References

  1. 1,0 1,1 Clark, R,B., 1999. Marine pollution. Oxford University press, Fourth edition, pp 161
  2. 2,0 2,1 Biology of marine birds. Schreiber, E.A. & Burger, J. (Eds). 2002. Boca Raton, Florida: CRC Press. 722 pp.
  3. Debacker, V.; Holsbeek, L.; Tapia, G.; Gobert, S.; Joiris, C.R.; Jauniaux, T.; Coignoul, F.; Bouquegneau, J.-M. (1997). Ecotoxicological and pathological studies of common guillemots Uria aalge beached on the Belgian coast during six successive wintering periods (1989-90 to 1994-95). Dis. Aquat. Org. 29(3): 159-168
  4. van den Heuvel-Greve, M.J.; Hoekstein, M.S.J.; Lefèvre, F.O.B.; Meininger, P.J.; Vethaak, A.D. (2003). Mogelijke oorzaken van slecht broedsucces in de visdiefkolonie bij Terneuzen; Stand van zaken en aanbevelingen. Rapport RIKZ, 2003.037: Middelburg, the Netherlands. 38 pp.


The main author of this article is Daphnis De Pooter
Please note that others may also have edited the contents of this article.