5/20/2015  |   10:30 - 10:45   |  101A

INTRODUCTION: TRANSITIONS IN UNDERSTANDING DIDYMOSPHENIA GEMINATA The widespread, yet elusive, diatom Didymosphenia geminata has captured the attention of scientists, managers, and policy makers alike. The increasing incidence of nuisance levels of benthic mats of D. geminata globally continues to drive efforts to better understand the basic biology and ecology of this species. Despite these efforts, environmental triggers to mat development as well as the impact to ecosystem processes and seasonal dynamics remain unclear. Recent and ongoing research examines phosphorus availability as a contributor to mat development and stalk length. Yet, the influence of other nutrients and whether the biogeochemical cycles are altered in the presence of D. geminata continues to be enigmatic. As the number of ecosystems containing D. geminata mats have increased over the last decade, it is imperative that the transition in understanding from the research of the past few decades, pushes us forward to a better understanding of the influence D. geminata may have on food web dynamics, ecosystem processes, and nutrient cycling in these oligotrophic lotic ecosystems.

Lisa Kunza (Primary Presenter/Author), South Dakota School of Mines and Technology, lisa.kunza@sdsmt.edu;


Carole-Anne Gillis (Co-Presenter/Co-Author), Gespe'gewaq Mi'gmaq Resource Council, gilliscaroleann@hotmail.com;

5/20/2015  |   10:45 - 11:00   |  101A

DIDYMO: IT'S ALL ABOUT THE STALKS If Didymosphenia geminata did not exhibit extraordinary extracellular polymeric substance (EPS) synthesis, it would not have attracted world-wide attention. Prodigious stalk production by D. geminata sets it apart from other diatoms and defines “bloom”, “nuisance” for this species. When considering diatoms, one usually conjures up images of smooth, clean, beautifully patterned silica frustules. In nature the glass “shoebox” is covered with slimes and a variety of EPSs that mediate interactions with the outside world. Diatom EPSs can self-assemble into specialized structures including tubes, apical pads, adhering films, fibrils, motility polymers and stalks. These provide for protection, adhesion, cohesion, motility, buoyancy, signaling, etc. D. geminata is valuable as a model system for study of EPS extrusion and self-assembly. Detailed examination of the chemistry, ultrastructure, molecular biology and physiology of stalk production allows for explanation of the dramatic nature of the recent proliferation of Didymo mats world-wide.

Michael Gretz (Primary Presenter/Author), Michigan Technological University, mrgretz@mtu.edu;

5/20/2015  |   11:00 - 11:15   |  101A

CAN CHANGES IN THE VALVE MORPHOLOGY OF DIDYMOSPHENIA GEMINATA AMONG BLOOM POPULATIONS HELP EXPLAIN RECENT INVASIONS? In the last two decades, the diatom Didymosphenia geminata has produced nuisance blooms in many parts of the world that had previously been free of this problem. Recent blooms could be caused either by the introduction of a particularly aggressive strain spreading into new areas or environmental changes that would cause locally present but cryptic populations to bloom. Using landmark-based shape analysis, we examine patterns in valve morphology among and within populations of D. geminata in two main areas: across North American, and New Zealand. The patterns of shape variation in North America were low within a population but often distinct among populations suggesting the environmental change model. While relatively low variability in valve shape within and among New Zealand populations is consistent with the Aggressive Colonization model which supports the prevailing notion that D. geminata is non-native in that country.

Robert Pillsbury (Primary Presenter/Author), University of Wisconsin Oshkosh, pillsbur@uwosh.edu;


Brenna Glas (Co-Presenter/Co-Author), University of Wisconsin Oshkosh, brenna.glas@gmail.com;

5/20/2015  |   11:15 - 11:30   |  101A

DIDYMO IN PINE CREEK, PENNSYLVANIA: ENVIRONMENTAL FACTORS CONTROLLING DISTRIBUTION AND PLANS FOR FUTURE RESEARCH In 2013, Didymosphenia geminata (didymo) was first documented in Pine Creek, a highly recreated tributary to the Susquehanna River in north-central Pennsylvania, USA. Environmental DNA monitoring has since confirmed that didymo is confined to one tributary and from there downstream throughout Pine Creek. Preliminary data suggest that didymo coverage is highest during the late fall months in this free flowing system. Longitudinal observations indicate that dissolved phosphorus concentrations may limit the spatial distribution of didymo to cold, nutrient poor headwater reaches. Other stalked diatoms (Gomphoneis sp.) have been observed in adjacent tributaries with incrementally higher phosphorus concentrations. Upcoming research is planned that will examine the current and historic distribution of didymo throughout Pine Creek and surrounding watersheds in Pennsylvania. Habitat suitability of 17 Pennsylvania watersheds will be determined using a combination of continuous instream water chemistry, dissolved phosphorus, and stream morphology data. Additionally, the physiologically important fatty acid content of didymo vs. non-didymo biofilms will be examined. This research is intended to provide much needed technical understanding of didymo in the mid-Atlantic region, USA.

Matthew Shank (Primary Presenter/Author), Susquehanna River Basin Commission, mshank@srbc.net;

5/20/2015  |   11:30 - 11:45   |  101A

MACROINVERTEBRATE STRUCTURAL AND CONSUMPTION RESPONSES TO DIDYMOSPHENIA GEMINATA MATS IN THE UPPER TENNESSEE RIVER WATERSHED Didymosphenia geminata (Didymo) mats can blanket stream substrata, changing habitat and food resource availability for benthic species. Given that eradication of Didymo from a stream is unlikely, it is important to critically assess mat impacts on ecosystem structure and function. We studied the relationships among benthic macroinvertebrates and Didymo in three Tennessee streams to assess changes in community composition and food resource use. Similar to previous studies, total invertebrate abundance consistently increased with increasing Didymo abundance, attaining a 6-fold increase in mats. Few correlations with specific groups were found. Emphemerella sp. was the most abundant EPT genera and its abundance decreased with increasing Didymo in two streams. However, Emphemerella were overall most abundant at the site with highest Didymo coverage. Despite little influence on composition, stable isotope analysis suggested that Didymo mats shifted invertebrate consumption away from rock biofilms to biofilms growing on macrophytes and leaves. Didymo cells were only a major food resource in one stream, and for only isopods, snails, and crayfish. Overall, Didymo mats had a stronger impact on macroinvertebrate resource use than on their composition.

Justin Murdock (Primary Presenter/Author), Tennessee Technological University, jnmurdock@tntech.edu;


Natalie Knorp (Co-Presenter/Co-Author), Tennessee Tech University, neknorp42@students.tntech.edu;


Lucas Hix (Co-Presenter/Co-Author), Tennessee Tech University, lahix42@students.tntech.edu;

5/20/2015  |   11:45 - 12:00   |  101A

EXPLORING THE IMPACT OF DIDYMOSPHENIA GEMINATA NUISANCE GROWTHS ON JUVENILE ATLANTIC SALMON Since 2006, nuisance growths of the diatom Didymosphenia geminata (didymo) have occurred in the Restigouche River system in eastern Canada. These dense mats have shifted macroinvertebrate community structure and prey abundance for juvenile Atlantic salmon (JAS). To understand the impacts of didymo on JAS, we assessed its effect on prey production, location, and availability. In parallel, we outlined the impact of mats on prey-predator interactions, habitat selection, and growth rates of JAS. Increasing didymo coverage lead to a significant positive relationship between proportions of benthic forays vs. drift forays (R2 = 0.54, p < 0.001). This shift in foraging behavior was not triggered by limited drifting prey availability. Isotopic signatures of JAS in didymo-affected sites suggest that these consumers have a more depleted diet than those in didymo-free sites. As for habitat selection, JAS site fidelity is sustained with increasing didymo cover. JAS daily weight gain is significantly lower in didymo-affected sites than didymo-free sites (p < 0.001). Underlying mechanisms by which D. geminata alters Atlantic salmon habitat will be discussed and the importance of thresholds dynamics will be highlighted.

Carole-Anne Gillis (Primary Presenter/Author), Gespe'gewaq Mi'gmaq Resource Council, gilliscaroleann@hotmail.com;


Normand E. Bergeron (Co-Presenter/Co-Author), Institut national de la recherche scientifique, Centre Eau Terre Environnement, normand.bergeron@ete.inrs.ca;