Mary Coyle Student Corner Your Ugly Neighbor: Rock Snot, A Native Nuisance

ppearing in rivers like an alien invader, Didymosphenia geminata Ahas garnered universal disgust, frustration and the worst nickname of all algal species, “rock snot.” This stalked is notorious for unsightly, grayish- brown mats that form along the bottom of oligotrophic rivers and streams (Figure 1).These mats range from small tufts along the apical surface of substrate to mats that cover the entire stream or river bottom to depths exceeding 20 cm. Due to the physical structure of the stalks, D. geminata mats have a significant impact on the aesthetic and biological characteristics of river systems. Beyond its unsightly appearance, D. geminata nuisance mats snag fishing gear and alter macroinvertebrate community Figure 1. Didymosphenia geminata on stream bottom rock (A) and nuisance mat (B) in the structure and near-substrate hydrology. Kootenai River, Libby, MT. Sections of rivers that have heavy mat coverage have decreased densities of conditions are commonly found below kilometers downstream of Libby Dam, taxa of large-bodied macroinvertebrates dams, leading to a high prevalence while patchy mat coverage continues of Ephemeroptera (mayflies), Plecoptera of nuisance mats in the tailwaters of for another 49 km downstream and (stone flies), and Trichoptera (caddis impounded systems. While predominantly persists for 10 months out of the year flies), known as EPT taxa, while the a lotic (flowing water) issue, nuisance (Figure 2). Impounded by Libby Dam, density of small-bodied taxa such as mats have been known to occur at lake the tailwaters of the Kootenai River, Chironomidae (midges) increased. This outlets and along shorelines that have where mat coverage is greatest, has an could alter the composition of local significant wave action. average soluble reactive phosphorus fisheries by reducing prey abundance for Historically, the occurrence of (SRP) concentration below detection (0.5 those species that key in on large EPT D. geminata mats has been observed µg/L) and nitrate + nitrite concentrations taxa. However, while the appearance throughout Europe since the mid-19th >200 µg/L. Nitrogen concentrations in the of these infuriating mats may mimic an century. However, these mats generally Kootenai River have steadily increased invasion, this diatom may, in fact, be a red persisted for a short period of time over the past nine years and are predicted flag of changes in the environment at a resulting in little public attention. The to continue to rise as a result of upstream global scale. current D. geminata mats that are anthropogenic activities in the watershed. receiving attention throughout the United Background States and other parts of the world are of Native Nuisance vs. Invasive Status Counter to the typical occurrence a different nature. These “nuisance mats” As a microscopic member of of nuisance algae in systems with high are defined as those that extend >1km the aquatic community, a shift to a nutrients, D. geminata forms nuisance that persist for several months of the highly noticeable macroscopic state is mats in winter in cold rivers with low year (Spaulding and Elwell 2007). The noteworthy. However, without a historical nutrient concentrations (especially Kootenai River in northwest Montana, reference of D. geminata as part of phosphorus – P), high light availability, USA has mat coverage over 70 percent of the periphyton, the occurrence of mats and stable bedrock. These habitat the river bed that extends at least 32 river results in a public perception that an

42 Summer 2015 / NALMS • LAKELINE Figure 2. Photograph of the Kootenai River bottom with >80% Didymosphenia geminata, nuisance coverage (A). Close up of nuisance mat,“rock snot”(B). invasion is underway. Unfortunately, this examined the commonality of this diatom the presence of a mat, amount of shade misconception has led to the widespread and its prevalence for nuisance mats and size of the water body were also belief that the species is an invasive in the throughout the intermountain northwest. recorded on data sheets accompanying United States. Historically, D. geminata each tube. Tubes with samples preserved was described as a rare diatom located Regional Distribution with Lugol’s iodine and the data sheet only at northern latitudes and it was not Algal scrapings were collected from were then mailed to me at the University considered an invasive until extensive sites across Montana and with of Idaho for analysis. nuisance mats were recorded from New an emphasis on areas with records of To analyze the samples, I examined York to Montana in the 1990s and 2000s. visual sightings of mats. To increase the multiple subsamples from each sample In 1989, persistent, nuisance mats area sampled, I enlisted the assistance by placing approximately 5–8 mL onto a were first recorded throughout central of federal (USFS, EPA, USGS) and glass microscope slide, covering it with Vancouver Island, Canada, in pristine state agencies (Montana Fish, Wildlife a cover slip and examining them with river systems and an association was and Parks and Idaho Department of the aid of a compound microscope at made between the presence of mats Fish and Game), private individuals 120×. If 5 or more cells of D. geminata to popular fishing locations (Bothwell (e.g., fly fishers or interested citizens), were found, a positive detection et al. 2009). Further tests showed that and personnel from non-governmental was recorded. A digital photograph D. geminata cells could remain viable organizations (NGOs) such as Trout (Figure 3) was taken of the cell and the in damp felt-soled waders for 50 days Unlimited (TU), Kelly Creek Fly remaining algae scraping was dried on (Kilroy et al. 2007), confirming the Casters (KFC), and the Federation of Fly an index card to create a voucher for plausibility that anglers and other Fishers (FFF). PowerPoint presentations that sample. Photograph number, stream recreationists were moving this diatom were given to several of the larger characteristics, and coordinates were all among rivers. However, as mats have organizations (TU Libby, KFC, and recorded on the envelope that held the continued to appear and research has IDFG) to disseminate information about algae scraping. Characteristics viewed in matured, patterns have begun to emerge the ecology of D. geminata, methods to the subsample such as presence of stalk and the concept of this species being an collect samples, and how to identify D. material from the D. geminata cells were invasive in the northern hemisphere is geminata mats. also recorded. All data were then entered being refuted, especially given historical Volunteers were asked to collect a into a Microsoft Access database that recorded dating to 1866 confirming its scraping of algae from various depths and will be available online to researchers or presence in Montana. Rather, changes rocks at one location to provide a diverse interested parties within the next year. in water quality conditions are being sample. The sample was placed in a 15 D. geminata detections from this linked to the presence of nuisance mats. ml centrifuge tube at least ¼ to ½ full, study and Tait (2010) were plotted on a To investigate this hypothesis throughout labeled with the name of the river, date, GIS map with ArcMap v. 10.2.2. This a D. geminata mat affected region, I and location. Other information such as map provides a reference of D.geminata

Summer 2015 / NALMS • LAKELINE 43 percent of the rivers had D. geminata P limitation may be increases in nitrogen as a normal member of the periphyton from atmospheric and terrestrial community (Figure 4). This survey clearly sources. Globally, nitrogen production demonstrated that D. geminata is common for agriculture, from the consumption throughout the region and usually occurs of fossil fuels, and from other human in a “well-behaved,” non-nuisance/non- activities has reached all-time highs mat phase. Data collection and synthesis within the last decade (Gu et al. 2013). will continue throughout 2015 to This massive shift has had wide-reaching increase our understanding of the species effects on the nitrogen cycle, including throughout the United States. increased wet and dry nitrogen deposition. This increase of nitrogen within lentic and A Native Nuisance lotic systems has the potential to affect As this study has shown, D. geminata the N:P ratio, resulting in phosphorus is common throughout the intermountain limitation. northwest. Supporting the historical To evaluate this hypothesis, I records of D. geminata as native species conducted mesocosm studies near Libby in Idaho and Montana, the question Dam, Montana, investigating phosphorus remains, what shifts in the environment, enrichment as a management strategy including possible changes in water study in March to September, 2013 and Figure 3. Didymosphenia geminata cells in an quality, causes D. geminata to move into January to May, 2014. Results from algae scraping from Cedar Creek in northwest a nuisance mat-forming phase from a these studies clearly showed that P Montana 2014. well-behaved member of the periphyton enrichment suppressed the stalk growth community? What threshold is the of D. geminata at all concentrations (0.5, trigger? And finally, what, if anything, can 1.5, 2, 3, 5 and 8 µg/L) of P added, and presence throughout the U.S. in 2014. be done to reverse this trend across the that algal diversity and biomass increased From the algae scrapings and sequential landscape? significantly. mapping of D. geminata cells, the To provide a complete story, a commonality of this algal species in the Limiting Nutrients mesocosm study investigating the region has been clarified (Figure 4). Of Phosphorus limitation (< 2 µ/L) has response of mats to changes in the the 127 creeks and rivers surveyed in been strongly linked to nuisance mat nitrogen to phosphorus ratio is currently Idaho and Montana, 52 percent had D. growth (Kilroy and Bothwell 2012). underway. This study will help determine geminata as part of the algal community. Given phosphorus concentrations have if increasing nitrogen in an already Of those with D. geminata, only 32 remained relatively stable in the Kootenai phosphorus limited system will continue percent had visible mats, while 68 River, a potential mechanism increasing to lead to increasing nuisance mats or if

Figure 4. Didymosphenia geminata distribution throughout Idaho and western Montana collected by authors and volunteers. Yellow dots are confirmed presence ofD. geminata cells with no mat presence. Red dots are confirmed presence of cells and mats ofD. geminata and blue dots are algal scrapings that were negative for D. geminata.

44 Summer 2015 / NALMS • LAKELINE the threshold has already been reached. At rates and bloom formation in relation Mary Coyle is a Ph.D. the conclusion of these studies, my goal is to ambient dissolved phosphorus student of natural to be able to make recommendations for concentration. Freshwater Biology, 57: resources at the University the management of D. geminata mats in 641-653. of Idaho. A native of the Kootenai River. Spaulding, S. and Elwell, L. 2007. McCall, Idaho, and a fly Increase in nuisance blooms and fishing enthusiast, she is Conclusion geographic expansion of the freshwater passionate about restoring D. geminata is an unsightly nuisance diatom Didymosphenia geminata. U.S and protecting water that many wish would just wash away. Geological Survey Open File Report resources throughout the However, this diatom may be an indicator 2007. Pacific Northwest. Her graduate research is focused of a much larger environmental issue. Tait, C. 2010. Aquatic invasive species on developing management strategies for Didymo Understanding the driving mechanism database. United States Forest Service. nuisance mats in the Kootenai River of Libby, MT. behind the dramatic shift of the http://www.fs.usda.gov/Internet/FSE_ c microscopic native diatom to the ugly DOCUMENTS/stelprdb5182307.pdf macroscopic nuisance is essential to identify viable management strategies and understand ecosystem health. While the Kootenai River has an extensive water quality dataset, for most river systems Large Lake Aeration Design & Consultation with significantD. geminata nuisance mats, long-term water quality data are patchy or non-existent, making it difficult to detect consistent and widespread regional trends. To further understand this complex issue, efforts to compile mat (nuisance or otherwise) locations, cell locations, and related water quality data are imperative. Understanding global environmental health trends is an enormous undertaking but by working to understand this perplexing diatom, I aim to gain valuable insights. If you are interested in providing algae scrapings for D. geminata detections 800-432-4302 and the Didymo Database, please contact www.vertexwaterfeatures.com Mary Coyle at rocksnotresearch@gmail. com.

References Bothwell, M.L., D. Lynch, H. Wright and J. Denisger. 2009. On the boots of fishermen: The history of didymo (HOLSINGER . . . Contintued from page 20) blooms on Vancouver Island, . Fisheries, 34: 282-388 and Anatoxin-a in Drinking Water by Liquid Chromatography Electrospray Gu, B., J Chang, Y. Min, Y. Ge, Q. Zhu, Ionization Tandem Mass Spectrometry (LC/ESI-MS/MS). EPA 815-R-009. J.N. Galloway and C. Peng. 2013. World Health Organization (WHO). 1999. Toxic Cyanobacteria in Water: A guide The role of industrial nitrogen in the to their public health consequences, monitoring and management. Bartram, J. and global nitrogen biogeochemical cycle. Chorus, I. (Eds). CRC Press, London. Scientific Reports, 3:2579 Kilroy, C., A. Lagerstedt, A. Davey and DISCLAIMER K. Robinson. 2007. Studies on the The views expressed in this article are those of the individual author and do not survivability of the invasive diatom necessarily reflect the views and policies of the U.S. Environmental Protection Didymosphenia geminata under a Agency. range of environmental and chemical conditions. Natl. Inst. Of Water and Atmos. Res., Christchurch, N.Z. Hannah Holsinger is an environmental scientist in EPA’s Office of Ground Water Kilroy, C. and M.L. Bothwell. 2012. and Drinking Water. She is based in Washington, DC, where she serves as the Didymosphenia geminata growth drinking water program’s cyanotoxin team lead. c

Summer 2015 / NALMS • LAKELINE 45