Rapid colonization of new habitats in the Wadden Sea by the ovoviviparous Littorina saxatilis (Olivi)

Abstract

The intertidal periwinkle Littorina saxatilis completely lacks larval dispersal and adult vagility is low. Although this suggests a low dispersal rate, L. saxatilis is frequently found in recently established habitats 'exotic' to the Wadden Sea. Populations occur on man-made structures like dikes, breakwaters and groynes, some of which are not older than several years. Furthermore, L. saxatilis is found on marsh grass Spartina anglica, introduced to the Wadden Sea in the 1920s and 1930s, as well as on mats of green macroalgae, which have become an abundant feature on the tidal flats since the late 1970s. Seagrass beds are likely to be the original habitat of L. saxatilis in the Wadden Sea. Since seagrass populations have dramatically declined over the last decades, colonization of new habitat types enabled L. saxatilis to maintain its Wadden Sea populations despite a changing environment. Colonizers can reach new habitats by means of passive transport, especially by rafting on macrophytes and by aerial dispersal attached to birds. In the Wadden Sea, the ovoviviparously reproducing L. saxatilis has demonstrated its ability to successfully found new populations with only a few individuals. No reduction of genetic variability (founder effect) was observed in recently established populations.