Award: OCE-1039513

The winter of 1962-63 in Europe was the coldest since 1740 and had catastrophic effects on intertidal populations, including mass mortality of many species and contraction of geographic ranges by hundreds of kilometers. Ecologically dominant "ecosystem engineering" species suffered extensive mortality and some species and their associated communities took almost 50 years to return to their previous geographic range limits. The winter of 2009-2010 was among the 7 coldest of the past century, and ranked third coldest since 1962-63, according to the Hadley Centre monthly Central England Temperature. Based on MODIS satellite measurements and high resolution gridded ICOADS data, sea surface temperature (SST) during the winter of 2009-10 in Europe appears to have been virtually identical that of 1962-63 (Fig. 1). The aftermath of this winter offered an outstanding opportunity to test the mechanisms controlling the biogeographic limits of major ecosystem engineering species in rocky and sedimentary intertidal habitats on a continental scale, and to understand the role of rare climatic events in controlling continental patterns of community composition. During the summers of 2010 and 2011 we surveyed the continental coast of Europe from Central Portugal to the eastern English Channel, as well as the coast of England, Wales and Scotland, at 20 to 50 kilometer intervals and measured the abundance of important intertidal species. We examined a northern barnacle species Semibalanus balanoides, whose reproduction is blocked by warm winter conditions. We predicted that it should have highly successful reproduction because of the cold winter of 2009-2010. After more than 5 decades of northward retreat due to warming winters, that species expanded its range by 80 to 200 kilometers in 3 different geographic regions after the cold winter of 2009-2010, and was seen in locations where it had not been observed in 40 to 60 years. The marine decorator worm Diopatra is a southern species whose reproduction is blocked by cold summer conditions. We predicted no change in its distribution because the summers of 2009-2010 were warmer than average, and as expected, we saw no change. We hypothesized that the subtropical marine mussel Mytilus galloprovincialis, and Chthamalus barnacles would suffer only reproductive failure in the cold winter. Consistent with our predictions, Chthamalus young of the year were rare in the English Channel in regions where adult Chthamalus populations had been expanding in recent warming decades. Mytilus galloprovincialis adults in the English Channel were common in regions where their populations had been expanding due to long term warming, indicating that adult survival was unaffected by the cold conditions. Our results indicate that the geographic distribution of species is affected by long-term climate change, but that long-term change in biogeography can be reversed by extreme events, with consequences that can potentially last for decades, depending upon the longevity of species and upon their rates of dispersal. Our project supported research experiences by both undergraduate and graduate students, who interacted with European scientists, who made a total of 8 presentations of their results at international scientific conferences, and who were co-authors of a total of 5 papers published in the scientific literature. Two of the students developed collaborations with European scientists which led to further research opportunities during the second field season of the project. The principal investigators of the project developed new research collaborations in the UK, France, Spain and Portugal, which will be continued with new funding from NSF and NASA. Last Modified: 10/03/2011 Submitted by: David S Wethey