Scientific literature on the origins of Didymo , felt soled wading boots , and vectors for some aquatic invasive species

We outline, in chronological sequence, the events and findings over 25 years that have shaped our understanding of Didymosphenia geminate (Lyngbye) M. Schmidt blooms. Starting with the first appearance of D. geminata mats in streams on Vancouver Island in the late 1980s and followed years later by blooms in Iceland, South Dakota and Poland, D. geminata blooms were enigmatic for nearly 20 years. Early papers exploring whether blooms were caused by environmental change consistently failed to identify any specific factor(s) associated with their onset. Following the D. geminata outbreak in New Zealand in 2004 that seemed to result from an introduction of the species, the possibility that blooms that had previously occurred elsewhere in the world might also be explained by the introduction and movement among watersheds of a new variant with a bloom-forming tendency was touted and widely accepted. Now, however, the identification of very low soluble reactive phosphorus (SRP; below ∼2 ppb) as the proximate cause of bloom formation, has led to the more likely explanation that D. geminata blooms are the result of large-scale human intervention in climatic, atmospheric and edaphic processes that favour this ultra-oligotrophic species. In this new view, blooms of D. geminata are not simply due to the introduction of cells into new areas. Rather, bloom formation occurs when the SRP concentration is low, or is reduced to low levels by the process of oligotrophication. Mechanisms that potentially cause oligotrophication on global and regional scales are identified. Taylor, B. W; and M. L. Bothwell. 2014. The origin of invasive microorganisms matters for science, policy, and management: the case of Didymosphenia geminata. Bioscience 64:531-538. http://legislature.vermont.gov/assets/Documents/2016/WorkGroups/House%20Fish%20and%20Wildlife /Bills/H.5/Witness%20Testimony/H.5~Eric%20Palmer~Origin%20of%20Invasive%20Microorgani sms%20for%20Science,%20Policy%20and%20Mgmt~3-11-2015.pdf Abstract: The value of distinguishing native from nonnative invasive species has recently been questioned. However, this dichotomy is important for understanding whether a species’ successful dominance is caused by introductions, changing environmental conditions that facilitate an existing population, or both processes. We highlight the importance of knowing the origin of hard-to-detect invasive microorganisms for scientific research, management, and policy using a case study of recent algal blooms of the stalk-producing diatom Didymosphenia geminata. Nuisance blooms have been reported in rivers worldwide and have been hastily attributed to introductions. However, evidence The value of distinguishing native from nonnative invasive species has recently been questioned. However, this dichotomy is important for understanding whether a species’ successful dominance is caused by introductions, changing environmental conditions that facilitate an existing population, or both processes. We highlight the importance of knowing the origin of hard-to-detect invasive microorganisms for scientific research, management, and policy using a case study of recent algal blooms of the stalk-producing diatom Didymosphenia geminata. Nuisance blooms have been reported in rivers worldwide and have been hastily attributed to introductions. However, evidence indicates that blooms are probably not caused by introductions but, rather, by environmental conditions that promote excessive stalk production by this historically rare species. Effective responses to invasive microorganisms depend on knowing whether their proliferation is caused by being nonnative or is the result of changing environmental conditions that promote invasive characteristics of native species. Lavery, J. M.; J. Kurek; K. M. Ruhland; C. A. Gillis; M. F. J. Pisaric; and J. P. Smol. 2014. Exploring the environmental context of recent Didymosphenia geminata proliferation in Gaspesie, Quebec, using paleolimnology. Canadian Journal of Fisheries and Aquatic Sciences 71:1-11. Abstract: Management authorities often perceive Didymosphenia geminata (didymo) as an invasive, nuisance diatom species that has been introduced to eastern Canada; however, observations from early 20th century diatom surveys challenge this characterization. We apply paleolimnological techniques to place recent didymo blooms from Gaspésie, Quebec, into historical and environmental context. Sedimentary diatom assemblages were examined from Lac Humqui (a headwater lake) and Lac au Saumon (a lake with an inflowing river currently supporting blooms). The Lac Humqui assemblage experienced a broad-scale shift in their dominant life strategy with declines in fragilarioid taxa and increases in planktonic diatoms (i.e., Cyclotella–Discostella species) that began_1970 and increased to modern abundances_1990. Strong relationships between this diatom shift and increases in regional air temperatures and earlier river ice-out dates are consistent with longer growing seasons and enhanced thermal stability in Lac Humqui. Didymo was observed throughout the Lac au Saumon core, demonstrating that it has been present in the region since at least _1970. Our paleolimnological evidence indicates that blooms likely form in response to regional consequences of climate warming, rather than human introduction. Management authorities often perceive Didymosphenia geminata (didymo) as an invasive, nuisance diatom species that has been introduced to eastern Canada; however, observations from early 20th century diatom surveys challenge this characterization. We apply paleolimnological techniques to place recent didymo blooms from Gaspésie, Quebec, into historical and environmental context. Sedimentary diatom assemblages were examined from Lac Humqui (a headwater lake) and Lac au Saumon (a lake with an inflowing river currently supporting blooms). The Lac Humqui assemblage experienced a broad-scale shift in their dominant life strategy with declines in fragilarioid taxa and increases in planktonic diatoms (i.e., Cyclotella–Discostella species) that began_1970 and increased to modern abundances_1990. Strong relationships between this diatom shift and increases in regional air temperatures and earlier river ice-out dates are consistent with longer growing seasons and enhanced thermal stability in Lac Humqui. Didymo was observed throughout the Lac au Saumon core, demonstrating that it has been present in the region since at least _1970. Our paleolimnological evidence indicates that blooms likely form in response to regional consequences of climate warming, rather than human introduction. Kilroy, C., and M. L. Bothwell. 2012. Didymosphenia geminata growth rates and bloom formation in relation to ambient dissolved phosphorus concentration. Freshwater Biology 57:641-653. https://www.researchgate.net/publication/263198176_Didymosphenia_geminata_growth_rates_and_b loom_formation_in_relation_to_ambient_dissolved_phosphorus_concentration Summary 1. The bloom-forming freshwater stalked diatom Didymosphenia geminata is unusual among algae in that nuisance growths occur almost exclusively in oligotrophic waters. Current hypotheses to explain this phenomenon have assumed supplemental acquisition of phosphorus from novel sources within the stalk ⁄mat matrix. 2. We carried out a synoptic survey of river sites in the South Island, New Zealand, to determine whether D. geminata cell division and stalk development (measured as mat coverage or standing crop) were related to ambient phosphorus concentrations in the overlying river water. 3. High coverage (>50%) by D. geminata was largely concentrated at sites with mean dissolved reactive phosphorus (DRP) <2 mg m) in the overlying water. Didymosphenia geminata was present at only one site with DRP >4 mg m)3, with very low coverage. Cell division rate (measured as the frequency of dividing cells, FDC) was positively correlated with mean DRP suggesting that division rates were controlled by the available phosphorus concentration in ambient river water. At the same time, FDC was negatively correlated with D. geminata standing crop (measured as an index incorporating percentage cover and mat thickness). 4. In a single river reach with a stable cross-channel gradient of total dissolved phosphorus (TDP) caused by inflows from a high-nutrient tributary, again we observed a negative correlation between percentage cover by D. geminata and concentrations of TDP. 5. Finally, we made a series of observations on D. geminata-dominated communities that had been exposed to water enriched with NO3 -N and PO4 -P for 4 weeks, followed by exposure to unenriched water. After 2 weeks of nutrient deprivation, D. geminata cell division rates declined by 60%, mean stalk length increased by 250%, and total carbohydrate quadrupled relative to initial values. The appearance of the community changed from a dark brown mat to a thick pale mat typical of D. geminata blooms. 6. All these results indicate that D. geminata cell division rates are actively controlled by concentrations of available phosphorus in the overlying water and that stalk production (represented by mat thickness and extent, stalk length and total carbohydrate) is inversely related to D. geminata cell division rates. They thus support an explanation for D. geminata blooms in oligotrophic rivers tied to enhanced stalk production in nutrient-poor waters, rather than through acquisition of additional phosphorus through recycling processes within the mat. Kilroy, C., and M. L. Bothwell. 2011. Environmental control of stalk length in the bloom-forming, freshwater benthic diatom Didymosphenia geminata (Bacillariophyceae). Journal of Phycology 47:981-989. Abstract: Blooms of the freshwater stalked diatom Didymosphenia geminata (Lyngb.) M. Schmidt in A. Schmidt typically occur in oligotrophic, unshaded streams and rivers. Observations that proliferations comprise primarily stalk material composed of extracellular polymeric substances (EPS) led us to ask whether or not the production of excessive EPS is favored under nutrient-limited, high-light conditions. We conducted experiments in outdoor flumes colonized by D. geminata using water from the oligotrophic, D. geminata–affected Waitaki River, South Island, New Zealand, to determine the relationship between D. geminata stalk length, cell division rates, and light intensity under ambient and nutrient enriched conditions. Stalk lengths were measured in situ, and cell division rates were estimated as the frequency of dividing cells (FDC). FDC responded positively to increasing light intensity and to nutrient additions (N+P and P). Under ambient conditions, stalk length increased as light level increased except at low ambient light levels and temperature. Nutrient enrichment resulted in decreased stalk length and negative correlations with FDC, with this effect most evident under high light. Our results are consistent with the hypothesis that extensive stalk production in D. geminata occurs when cell division rates are nutrient limited and light levels are high. Thus, photosynthetically driven EPS production in the form of stalks, under nutrient-limited conditions, may explain the development of very high biomass in this species in oligotrophic rivers. The responses of FDC and stalk length under nutrient replete conditions are also consistent with occurrences of D. geminata as a nondominant component of mixed periphyton communities in high-nutrient streams. Blooms of the freshwater stalked diatom Didymosphenia geminata (Lyngb.) M. Schmidt in A. Schmidt typically occur in oligotrophic, unshaded streams and rivers. Observations that proliferations comprise primarily stalk material composed of extracellular polymeric substances (EPS) led us to ask whether or not the production of excessive EPS is favored under nutrient-limited, high-light conditions. We conducted experiments in outdoor flumes colonized by D. geminata using water from the oligotrophic, D. geminata–affected Waitaki River, South Island, New Zealand, to determine the relationship between D. geminata stalk length, cell division rates, and light intensity under ambient and nutrient enriched conditions. Stalk lengths were measured in situ, and cell division rates were estimated as the frequency of dividing cells (FDC). FDC responded positively to increasing light intensity and to nutrient additions (N+P and P). Under ambient conditions, stalk length increased as light level increased except at low ambient light levels and temperature. Nutrient enrichment resulted in decreased stalk length and negative correlations with FDC, with this effect most evident under high light. Our results are consistent with the hypothesis that extensive stalk production in D. geminata occurs when cell division rates are nutrient limited and light levels are high. Thus, photosynthetically driven EPS production in the form of stalks, under nutrient-limited conditions, may explain the development of very high biomass in this species in oligotrophic rivers. The responses of FDC and stalk length under nutrient replete conditions are also consistent with occurrences of D. geminata as a nondominant component of mixed periphyton communities in high-nutrient streams. Bothwell, M. L., and C. Kilroy. 2011. Phosphorus limitation of the freshwater benthic diatom Didymosphenia geminata determined by the frequency of dividing cells. Freshwater Biology 56:565-578. https://www.researchgate.net/publication/230353517_Phosphorus_limitation_of_the_freshwater_bent hic_diatom_Didymosphenia_geminata_determined_by_the_frequency_of_dividing_cells Summary 1. Unlike other nuisance algal species, the freshwater benthic diatom Didymosphenia geminata typically forms blooms in low-nutrient rivers. The negative association between D. geminata blooming behaviour and nutrient levels appears at both catchment and smaller scales. We conducted a series of trials in streamside experimental channels colonised with D. geminata using water from the D. geminataaffected, oligotrophic Waitaki River, South Island, New Zealand to determine how elevated nitrate and phosphate concentrations affected D. geminata cell division. Because D. geminata blooms are typically most pronounced in unshaded waters, we also investigated the growth response to shading. In all experiments, we used the frequency of dividing cells (FDC) as a metric of cell division. 2. Concentrations of nitrate and dissolved reactive phosphorus (DRP) in the Waitaki River were very low (4 mg m)3 NO_3 -N and <1 mg m)3 DRP). In pilot trials, substrata colonized by D. geminata were subjected to enrichment by either switching the water source to Nand P-rich spring water or by adding a stock NO_3 _ PO3_4 solution. Both trials resulted in periods of rapid cell division lasting at least 8 days. 3. Experimental addition of NO_3 alone triggered an initial cell division which was not sustained. However, addition of PO3_4 alone or together with NO_3 resulted in prolonged elevation in cell division indicating that the cell division rate was P-limited. 4. Reduced light levels resulted in decreased FDC in D. geminata in both ambient and N, N + P and P-enriched river water. 5. Stimulation of D. geminata division rate by addition of PO3_4 above ambient levels confirms that, while blooming behaviour is often associated with oligotrophic rivers, the cells divide faster with greater levels of phosphorus enrichment. If Didymo weren’t already present everywhere, this is how it might spread: Bothwell, M. L., D. R. Lynch, H. Wright, and J. Densinger. 2009. On the boots of fishermen: the history of Didymo blooms on Vancouver Island, British Columbia. Fisheries 34(8):382-388. http://www.env.gov.bc.ca/wat/wq/studies/didymo-blooms.pdf Abstract: In 1989 blooms of the river benthic diatom Didymosphenia geminata (didymo) first appeared and rapidly spread among rivers on central Vancouver Island, covering the bottoms with thick, woollylooking mats. Although didymo is native to North America, extensive field surveys of rivers on Vancouver Island and other data indicate that didymo blooms are new. No known environmental changes were associated with the onset of didymo blooms. However the pattern of didymo spread among rivers on Vancouver Island correlates with the activity of fishermen and the commercial introduction and widespread use of felt-soled waders in the late 1980s. Since 1994 nuisance blooms of didymo have appeared in numerous other places in the Northern Hemisphere and South Island, New Zealand, all areas frequented by fishermen. Actions by government agencies to educate the public and restrict the use of felt-soled waders have been undertaken in some jurisdictions and at least one commercial manufacturer of waders will discontinue production of felt-soled models in the near future. NOTE: Bothwell later proved his own theory to be wrong (see above). In 1989 blooms of the river benthic diatom Didymosphenia geminata (didymo) first appeared and rapidly spread among rivers on central Vancouver Island, covering the bottoms with thick, woollylooking mats. Although didymo is native to North America, extensive field surveys of rivers on Vancouver Island and other data indicate that didymo blooms are new. No known environmental changes were associated with the onset of didymo blooms. However the pattern of didymo spread among rivers on Vancouver Island correlates with the activity of fishermen and the commercial introduction and widespread use of felt-soled waders in the late 1980s. Since 1994 nuisance blooms of didymo have appeared in numerous other places in the Northern Hemisphere and South Island, New Zealand, all areas frequented by fishermen. Actions by government agencies to educate the public and restrict the use of felt-soled waders have been undertaken in some jurisdictions and at least one commercial manufacturer of waders will discontinue production of felt-soled models in the near future. NOTE: Bothwell later proved his own theory to be wrong (see above). Kilroy, C., A. Lagerstedt, A. Davey, and K. Robinson. 2007. Studies on the survivability of the invasive diatom Didymosphenia geminata under a range of environmental and chemical conditions. National Institute of Water and Atmospheric Research Ltd, Christchurch, New Zealand, report CHC2006-116. http://www.biosecurity.govt.nz/files/pests/didymo/didymo-survival-dec-06-rev-may-07.pdf