Historical invasions of the intertidal zone of Atlantic North America associated with distinctive patterns of trade and emigration
▻http://www.pnas.org/content/106/20/8239.full
Abstract
Early invasions of the North American shore occurred mainly via deposition of ballast rock, which effectively transported pieces of the intertidal zone across the Atlantic. From 1773–1861, >880 European ships entered Pictou Harbor, Nova Scotia, as a result of emigration and trade from Europe. The rockweed Fucus serratus (1868) and the snail Littorina littorea (≈1840) were found in Pictou during this same period. With shipping records (a proxy for propagule pressure) to guide sampling, we used F. serratus as a model to examine the introductions because of its relatively low genetic diversity and dispersal capability. Microsatellite markers and assignment tests revealed 2 introductions of the rockweed into Nova Scotia: 1 from Galway (Ireland) to Pictou and the other from Greenock (Scotland) to western Cape Breton Island. To examine whether a high-diversity, high-dispersing species might have similar pathways of introduction, we analyzed L. littorea, using cytochrome b haplotypes. Eight of the 9 Pictou haplotypes were found in snails collected from Ireland and Scotland. Our results contribute to a broader understanding of marine communities, because these 2 conspicuous species are likely to be the tip of an “invasion iceberg” to the NW Atlantic from Great Britain and Ireland in the 19th Century.
#espèces_invasives, mais pas trop mobiles ce qui permet de les suivre sur (assez) longue période, ici, le #varech et le #bigorneau en #Nouvelle-Écosse
Article accessible. La conclusion :
We have demonstrated the value of a multidisciplinary approach for examining biological invasions. By combining historical, genetic, and ecological data, we refined understanding of 2 particular introductions while exploring limits of resolution for 4 fundamental questions in invasion biology: Where did the invader first become established? When did it arrive? Where did it come from? How did it get there? Beyond these immediate results, our data contribute to a broader understanding of marine communities. First, F. serratus and L. littorea must be the tip of an “invasion iceberg” involving a suite of associated, but less conspicuous, species that followed the same path from Great Britain and Ireland to North America through Nova Scotia. Communities on both sides of the Atlantic should now be examined for other invaders that have been considered indigenous or at best “cryptogenic”, with better ability to assess the role of source-specific genetic adaptation to invasion success. Second, all introductions must be evaluated against relevant ecological and evolutionary processes and integrated into our understanding of community structure and function, especially in terms of long-term changes and our perception of what is natural or desirable in our marine environment. It can be difficult to compare recipient and source habitats directly because many port areas are completely transformed from their 19th Century states. Nevertheless, adjacent areas can provide clues about habitat, ecotypic identity, and diversity that underlie our interest in eventual comparisons of community structure on northern Atlantic rocky coasts. Indeed, the emerging concern of “sliding baselines” in the assessment of our natural world requires that we know what came from where and when.