Collaborative Research: Cascading effects of an invasive seaweed on estuarine food webs of the southeastern US

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During the last decade, the Asian seaweed, Gracilaria vermiculophylla, has proliferated along high-salinity mudflats in several Georgia and South Carolina estuaries. The invasion is noteworthy because the mudflats in these estuaries were historically devoid of macrophyte-based primary production and structure. Gracilaria has few native analogues in these mudflat environments, and thus represents an opportunity to examine the ecosystem consequences of an invasion within an historically-unexploited niche. In theory, Gracilaria affects populations of species that are directly dependent on the invader for structure and food, as well as altering community- and ecosystem-level processes such as detrital production and food web structure. Through a combination of manipulative field experiments, laboratory assays and stable isotope analysis, the investigators will test three mechanisms by which Gracilaria influences native community structure. The novel structure and primary production generated by Gracilaria vermiculophylla may be 1) increasing rates of secondary production 2) increasing levels of mudflat microbial production through leeching of dissolved nutrients, and 3) increasing detrital input to microbial and macrobial food webs. This project will provide a mechanistic understanding of the multiple cascading impacts of an invasive species within the estuarine community. Species invasions that alter ecosystem functions are usually the most profound. These alterations are often generated by a small number of invaders that create physical structure, including important biogenic habitat, de novo. By altering physical structure, these non-native ecosystem engineers alter local abiotic conditions, interactions between species, and species composition. Highly influential invaders may also change food web structure and trophic flow of energy and materials. Such substantive food web changes can occur when an influential invader provides nutrients or resources that are different in quality, quantity or both. An invasive species that both provisions new physical structure and fundamentally alters food web structure could exert an overwhelming influence on native communities when these mechanisms act in synergy.The project also includes education and outreach components, especially mentoring. It will prepare two graduate and three undergraduate students for scientific careers by having them independently develop projects related to the project. Their research will integrate the traditional experimental techniques used to study invasive species with advanced analytic techniques of stable isotope analyses, PCR-based identification of gut contents, and enumeration of microbial communities. Consistent with their past projects and the goals of NSF, the PIs are committed to mentoring a diverse group of students across multiple educational levels (high school, undergraduate, graduate) and ethnicities. They will involve two high school science teachers through a "teacher as researcher" program to participate in field and laboratory projects. Each will conduct research and be expected to develop new unit plans for their classrooms. Finally, the PIs will continue to disseminate their results to the public through lectures, open house events at their institutions, as well as radio, newspaper, and television interviews. Finally, this study will be of immediate benefit to managers charged with mitigating the impacts of invasive species.