Award: OCE-1357386

Biological introductions, defined as the establishment of species in geographic regions outside the reach of their natural dispersal mechanisms, have dramatically increased in frequency during the 20th century and are now altering community structure and ecosystem function of virtually all marine habitats. To date, studies on marine invasions focus principally on demographic and ecological processes, and the importance of evolutionary processes has been rarely tested. This knowledge gap has implications for management policies, which attempt to prevent biological introductions and mitigate their impacts. This grant uses an invasive seaweed (Gracilaria vermiculophylla) as a model system to illustrate how combining multiple tools (population genetics, high-throughput phenotyping assays, and niche models) can help to assess the importance of phenotypic evolution in facilitating marine invasions. Gracilaria vermiculophylla is native to China, Korea, Russia and Japan, and has been introduced to every continental margin in the Northern Hemisphere. Using population genetics, we found that >95% of introduced thalli have a genetic signature similar to thalli of the Pacific coastline of northeastern Japan, strongly indicating this region served as the principal source of the introductions to North America and Europe. Notably, northeastern Japan exported the vast majority of the aquacultured oyster Crossostrea gigas during the 20th century, and both G. vermiculophylla and oysters thrive within shallow, soft-bottom and estuarine habitats. Thus, the preponderance of evidence suggests that G. vermiculophylla was inadvertently introduced with C. gigas shipments, and moreover, that northeastern Japan is a common source region for a several estuarine invaders in or near oyster beds (Figure 1). We also demonstrated a shift in mating system during the invasion. Native populations in the northwest Pacific Ocean were nearly always attached by holdfasts to hard substrata and, as is characteristic of the genus, haploid-diploid ratios were slightly diploid-biased. In contrast, along North American and European coastlines, introduced populations nearly always floated atop soft-sediment mudflats and were overwhelmingly dominated by diploid thalli without holdfasts. Introduced populations exhibited population genetic signals consistent with extensive vegetative fragmentation, while native populations did not. Thus, the ecological shift from attached to unattached thalli, ostensibly necessitated by the invasion of soft-sediment habitats, correlated with shifts from sexual to asexual reproduction and slight to strong diploid bias (Figure 2). Finally, we found that introduced populations have greater survivorship under extreme heat, cold and low-salinity stresses relative to Japanese source populations. The invasion of G. vermiculophylla was also accompanied by local adaptation within eastern North America, as populations from warmer, lower-latitude estuaries had greater heat tolerance than did populations from colder, higher-latitude estuaries. This cline recapitulates a parallel decline in native Japan and was generated at a remarkable rate, given that the introduction occurred within the last 20 years. We conclude that rapid evolution plays an important role in facilitating the invasion success of this and likely other marine species and reinforces the threat that introductions represent to nearshore ecosystems (Figure 3). This grant facilitated the training of 2 high school students, 6 undergraduates, 3 MS students and a postdoctoral associate. Three of these students (2 undergraduates and 1 MS students) are now enrolled in PhD programs, and the postdoc is now an Assistant Professor. The grant also facilitated a citizen-science program in close collaboration with a local non-profit educational center. A custom-built curricula for K-8 students in Charleston County elementary schools. Entitled "Lowcountry Algal Monitoring Program for Students" (or LAMPS) centers on statistics and marine ecology using "Case Studies" that are based on real data the students collect. Each month, we take pictures of long-term quadrats on a Charleston Harbor mudflat, and the students use a point-intercept method to assess percent cover of the invasive seaweed. Since Spring 2015, at least 3990 K-12 children have helped to generate data, and we?ve helped train 340 teachers from across South Carolina. (see http://www.patriotspointsciencespotlight.com/lamps.html for more details.) Last Modified: 05/30/2018 Submitted by: Erik E Sotka