EFFECTS OF POLYHALOGENATED AROMATIC-HYDROCARBONS AND RELATED CONTAMINANTS ON COMMON TERN REPRODUCTION - INTEGRATION OF BIOLOGICAL, BIOCHEMICAL, AND CHEMICAL-DATA

In eight Dutch or Belgian common tern (Sterna hi, undo) colonies, bree ding biology and food choice were determined, and 15 second eggs were collected from three-egg clutches for artificial incubation, biochemic al analysis and analysis of yolk-sac polyhalogenated hydrocarbon (PHAH ) levels. Results from these analyses were combined with biological da ta from the eggs remaining in each clutch. In some breeding colonies s evere flooding, rainy and cold weather, and extreme predation caused e xtensive losses of eggs and chicks. A relationship was found between y olksac mono-ortho polychlorinated biphenyl (mo-PCB) levels and main fo od species (fish or insects) of the adult terns before egg-laying. Col ony average breeding data differed only slightly, and were difficult t o relate to PHAH-levels. When the colonies were grouped after yolksac PHAH-patterns and main food species, significant differences in averag e egg laying date, incubation period, egg volume and chick weight coul d be related to differences in yolksac PHAH and retinoid levels, and h epatic ethoxyresorufin-O-deethylase (EROD) activity. The data from all colonies also were combined into one data-set and correlated with the biochemical parameters and PHAH levels. In summary higher yolksac PHA H levels or hepatic EROD-activity correlated with and later egg laying , prolonged incubation period and smaller eggs and chicks. Lower yolks ac retinoid- and plasma thyroid hormone levels, and a higher ratio of plasma retinol over yolksac retinoids correlated with later egg laying , prolonged incubation periods and smaller chicks and eggs. The dynami c environment of the terns had more obvious detrimental effects on bre eding success than PHAHs. However, the more subtle effects observed fo r PHAHs could still be of importance during specific stress circumstan ces. To monitor site-specific reproduction effects, tree-nesting birds feeding on relatively big and non-migrating fishes would be most suit able. The use of specific biomarkers for exposure and effect is recomm ended to establish a causal relationship between a certain class of po llutants and an adverse biological effect.