Brawley et al. 2009. Historical invasions of the intertidal zone of Atlantic North America associated with distinctive patterns of trade and emigration. doi: 10.1073/pnas.0812300106
Origins of invasive marine organisms
Trade and emigration from Europe to North America in the 19th century resulted in thousands of ships crossing the Atlantic Ocean. Shipping records from 1773-1861 indicate that nearly all ships arriving in Pictou Harbour, Nova Scotia originated in Scotland, England, or Ireland. Some of these ships brought marine organisms on the rocks used as ship ballast. Two invasive species, the rockweed Fucus serratus and the periwinkle snail Littorina littorea, have become common on Canada's North Atlantic coast, and the snail quickly became abundant on the Atlantic coast of the United States. By using genetic fingerprints and historical shipping records, Susan Brawley et al. determined that F. serratus and L. littorea found in Pictou Harbour likely originated in Great Britain and Ireland. Microsatellite analysis of F. serratus indicated 2 separate introductions to Nova Scotia: one originating in Galway, Ireland, and one in Greenock, Scotland. L. littorea showed a similar pattern, with 8 of the 9 cytochrome b haplotypes matching those from snails captured in Ireland and Scotland. These findings suggest that shipping records may provide a proxy for recognizing the introduction of invasive marine species, and the authors suggest that these species form the tip of the "invasive iceberg."