Hydrobiologia 309: 15-27, 1995. P. J. Mill & C. D. McQuaid (eds), Advances in Littorinid Biology. 15 © 1995 Kluwer Academic Publishers. Printed in Belgium. TBT effects on the female genital system of Littorina littorea: a possible indicator of tributyltin pollution Barbara Bauer 1 , Pio Fioronil, Imke Ide 2 , Stefanie Liebe 2 , Jorg Oehlmann 3 , Eberhard Stroben' & Burkard Watermann 2 l lInstitutfiir Spezielle Zoologie und Vergleichende Embryologie, Hifferstrasse 1, D-48149 MUnster, Germany 2 LimnoMar, Wulfsdorfer Weg 200, D-22926Ahrensburg, Germany 3 Internationales Hochschulinstitut, Markt 23, D-02763 Zittau, Germany Key words: Littorina littorea, reproductive failure, TBT contamination, biomonitoring, antifouling paints, histopathology Abstract Specimens of the prosobranch Littorina littorea (L., 1758) collected along the East Frisian North Sea coast in summer 1993 exhibited alterations of the pallial oviduct termed as intersex in response to tributyltin (TBT) pollution. The range of TBT body burden was between 150.9 and 1289.5 g as Sn kg -l (dry wt.). Five stages of intersex development (0-4) could be distinguished and are documented with scanning electron micrographs. In stages 2-4, which can be found in the direct vicinity of harbours and marinas, the morphological malformations of the oviduct inhibit successful copulation and capsule formation, resulting in sterilization. The intersex index (ISI, calculated as the average intersex stage of a population) and the average prostate length of females were used as parameters for the determination of intersex intensities in the populations. Both indices show significant and positive correlations to the TBT body burden of L. littorea and are promising parameters for TBT biomonitoring. A comparison of TBT bioconcentration factors with populations from England and France indicates that the threshold concentration for intersex development is in the range of 15 ng TBT as Sn/l. Morphometric analyses of the midgut gland revealed no significant differences between sampling stations. In the ovary a retardation and blockage of maturation (atresia) was observed in populations close to harbours. Lytic processes in ovary follicles were observed not only at TBT exposed sites but also at reference stations. Introduction Tributyltin (TBT) compounds used as biocides in antifouling paints and in various other formulations are known to produce a variety of malformations in marine animals, with molluscs being one of the most TBT- sensitive groups of invertebrates (for review Bryan & Gibbs, 1991). TBT-induced detrimental effects in Great Britain and France, e.g. malformations of oyster shells and the imposex phenomenon of prosobranchs, became evident in the 1980s. Consequently, legislative restrictions were drawn up to reduce TBT contamina- tion in coastal waters. The imposex phenomenon of prosobranchs has been successfully used as a biomon- itoring system to determine the degree of environmen- tal TBT pollution (e.g. Gibbs et al., 1987; Oehlmann et al., 1993). The established European imposex species for TBT biomonitoring (e.g. Nucella lapillus (L.), Hinia reticu- lata (L.), Ocenebra erinacea (L.)) are absent on the German North Sea coast or can only be found in restricted areas. The periwinkle Littorina littorea (L.) is the only prosobranch which is very common and can be sampled in sufficient numbers. In the present study the potential of L. littorea was evaluated for TBT biomonitoring. Littorina littorea is a shallow water species which lives on rocky and sandy shores. Though the bulk of the population occurs intertidally, some specimens can be found up to a depth of 15 m. Their geographical distri- bution ranges from Asturia to northern Norway in the