Evaluating records of trans-Atlantic dispersal of drifting disseminules to European shores.

Disseminules have drifted in long distance dispersal from the Americas to the coasts of Europe with records extending to the Arctic Ocean and southwards to the Macaronesian islands. The parent plants originate from tropical wetland forests to boreal conditions. Their disseminules undergo different ocean crossing times according to buoyancy duration. We use plastic-drift as a surrogate for the likely risks that disseminules endure during long-distance oceanic spread relating to their size, behaviour and losses from sinking. While origins of disseminules have a wide latitudinal biogeography we have used the records of the extensive strandings on Floridian, Bermudian and the east coast of North American shores as the region with which to compare the comparatively sparse arrivals in Europe. Studies on plastic drift show that the Atlantic current flow is mainly directed towards the northern coast of Ireland, that also covers the west coast of Scotland and south-west Britain. We have concentrated our records to this region, in particular to the Atlantic coasts of Ireland. Few disseminules arrive on European shores in a viable state, and for those that do, the temperate conditions may not suit germination. Some stranding events are likely to have anthropogenic involvement; but the great majority are most probably naturally distributed. Historically, the ethnographic significance suggests stranding events have taken place over centuries and most probably regularly took place during the Holocene. The increase of records in recent decades is likely to have been due to interested observers with access to taxonomic guides, the popular literature and on-line information.