The species in the Japanese knotweed complex (Fallopia japonica s.l. and its hybrids) are among the most invasive plants on earth. Their expansion and reproduction in the introduced range have been mostly due to vegetative reproduction, but observations of low seedling numbers and hybridization processes exist. Knowledge of factors affecting germination characteristics is essential if the risk of sexual reproduction is to be assessed, and its impact on the ability of the species to spread and adapt to different environments. This study aims to examine the germination success of Fallopia japonica s.l. seeds of different ages, quality, and storage conditions. Irrespective of age and even after natural overwintering in the soil, seeds germinated quite well (48-79%). Ungerminated seeds collected in autumn of 2008 were characterized by a low weight/length ratio (W/L), low nutrient concentrations, and a greenish tepal coloration. These differences may be due to alternative male taxa participating in the pollination process. Spring collected seeds were subject to strong predation by birds. In contrast to the high germination observed under laboratory conditions, seed germination or early establishment in the field was inhibited and only a few seedlings were observed. Although the factors that inhibit the establishment of mature seeds in the field remain unknown, there is a clear risk that sexual reproduction could gain importance in the future as a result of changing environmental conditions or genetic adaptation. Not only would this facilitate expansive dispersal by wind, but it might also increase the potential for further adaptation of the species complex.

Over the past 25 years, the grey seal (Halichoerus grypus) population in the North Sea increased on average at 5% per year, while founding a number of new colonies. Based on published data, this note compares recent trends in pup production at nine breeding sites, with focus on the German island of Helgoland. Since 1997, numbers born at Helgoland increased at 35% per year (95% CI: 29-42), reaching an all-time high of 53 in 2007. Yet, this was less than 1% of all grey seal oVspring in the North Sea area. Some other small stocks had similarly high growth rates of 20-50%, which must be explained by immigration from the larger colonies, as sustained autochthonous increase cannot exceed 13% per year in the species. Further, the Helgoland breeding stock increased signiWcantly faster than the neighbouring colonies at Amrum (13%) and in the Dutch Wadden Sea (20%), indicating higher oVspring survival and/or higher relative inXux of migrants. This is attributed to the fact that at Helgoland newborn seals are safe from Xoodwater. In the other two sites, in contrast, pups are born on sandbanks and are thus often hit by winterly storm tides, which poses a risk to their survival. Because of the favourable breeding conditions at Helgoland, this new colony is expected to soon become an important stronghold of the grey seal in the Dutch-German North Sea area.

No abstract

. 2ØØ1. This publication can be downloaded as a pdf-file from the EURING website: www.euring.org And also from the website of the Dutch Ringing Scheme: www.vogeltrekstation.nl The two former EURING code manuals, 'EURING Code Manual ' (1966) and 'Code Manual New EURING' (1979), can also be downloaded (pdf) from the two websites mentioned above.