Certain species of algae can have substantial socio-economic costs because they produce toxins that are harmful to other species in their environments, as well as to humans. Recently, a species of golden alga has exhibited a significant increase in its frequency and severity of toxic blooms in lakes and reservoirs nationally and globally. The spread of this species has been surprisingly rapid through US waterways during the last decade. To date, sixteen states have confirmed massive fish kills attributable to golden algae. This project will examine two hypothesized mechanisms for how invasive algal species become established in new environments. The first hypothesis is that enrichment of water with nutrients creates less diverse microbial communities, which are then less resistant to invasion. The second hypothesis is that invasion success is simply a function of the number of invaders that disperse to the new habitat. This research will conduct experiments in outdoor tanks at the University of Oklahoma Biological Station to test the ability of a lake community to resist invasion by golden algae. The experimental treatments will consist of different rates of introduction of golden algae and different levels of microbial diversity in the community, created through nutrient enrichment and quantified using DNA sequencing.
This study represents a test of the applicability of general ecological theory to understanding freshwater microbial diversity, but also provides insight into what controls freshwater harmful algal invasions. As such, the results from this project are of broad relevance to the management of freshwater ecosystems. Results will be disseminated through scientific presentations and journal publications, and also through outreach to local communities and K-12 students and teachers that visit the university biological station. This project supports the dissertation research of a graduate student.
Overview We conducted a mesocosm experiment using natural Lake Texoma (OK-TX) microbial assemblages to address the roles of propagule pressure (i.e., the number of individuals invading a given habitat) and community resistance to species invasion in a microbial system. Using the invasive harmful algal bloom species, Prymnesium parvum, we asked "what propagule size is necessary to result in a successful invasion of P. parvum?" and "do excess resources and subsequent community simplification reduce resistance to invasion of P. parvum?" Understanding and answering these questions is important because (1) excess nutrients and community simplification are well known phenomena associated with eutrophication of fresh waters, (2) blooms of P. parvum have become an increasingly common in freshwater ecosystems across southern North America causing massive fish kills, and (3) little, if anything, is known about the relevance to microbes of invasion ecology concepts derived from multi-cellular organisms. Findings of this study have also contributed to two public presentations, one chapter of Zamor’s dissertation, and are being prepared for publication in a scientific peer-reviewed journal. Findings In this mesocosm experiment we manipulated P. parvum propagule size (3 treatments: low, medium, and high) and nutrients (low and high) in 2-L bottles containing a natural microbial community isolated from Lake Texoma to assess their effects on P. parvum establishment success and the potential for interactions between propagule pressure and invasion resistance. We analyzed taxonomic composition of the microbial community by sequencing both the bacterial and eukaryotic hypervariable regions on the small subunit ribosomal DNA using high-throughput pyrosequencing. This produced approximately 800,000 sequences that we used to compare community diversity and to detect P. parvum presence. Manipulations of nutrients were effective in lowering observed microbial diversity. Additionally, at high propagule pressure eukaryotic diversity was also decreased. Interestingly, at high propagule pressure, bacterial diversity was increased. However, regardless of the biodiversity of the microbial assemblages, P. parvum successfully established in all high propagule pressure treatments. This suggests that propagule pressure overwhelmed any resistance effects and is potentially more important in determining the establishment success of P. parvum as a microbial invader. Training and Development This project has provided experience in both research and teaching skills to co-PI Richard Zamor. This project allowed Zamor to become proficient in numerous molecular methods including next-generation gene sequencing, bioinformatics and data processing, and project management. This included training with world-class genomics experts Bruce Roe and Fares Najar (Advanced Center for Genome Technology – Univ. of Oklahoma) and attending a workshop to learn the bioinformatics package ‘mothur,’ hosted by Pat Schloss (Univ. of Michigan). Through this project, Zamor also successfully initiated collaboration with Dave Caron (Univ. of Southern California) and his graduate student (Adriane Jones), and spent time training in Prof. Caron’s laboratory. Additionally this project enabled both undergraduate (Jeffrey Hayworth, training in bioinformatics) and graduate members of the lab (Jessica Beyer & Thayer Hallidayschult) to gain hands-on experience with molecular techniques. Outreach Activities Through this project, Zamor has successfully started an outreach program with Owasso High School, in Owasso, OK, to spread general background information that is fundamental to this project including information on invasive species, microbial ecology, harmful algae blooms, and limnology. This outreach program provides students a chance to experience zooplankton, algae, and invasive species up close under the microscope. Zamor has also included two junior graduate students in the lab (Hallidayschult and Beyer) in this outreach program to ensure that this outreach is maintained after the completion of his degree.
