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3: Boxplots with Anova results indicated, outlining relationships between Didymosphenia. geminata biomass (ash free dry mass) g.m-22 and a) the Lentic influence index (Arc-GIS estimated) (ANOVA, P<0.0005
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A thesis examining Didymosphenia geminata invasion ecology and organism biology in New Zealand rivers and streams.
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... Given the extensive alterations in stream habitat and consequent trophic effects on many components of stream ecosystems, we contend that D. geminata can be considered an ecosystem engineer (Bray 2014, Ladrera et al. 2018, Bray et al. 2020, Clancy et al. 2021. Ecosystem engineers influence the acquisition of resources of other species by physically altering their environment. ...
... The original area of the distribution of Didymosphenia geminata (Fig. 5.a) is North America and Europe, but it spread and bloomed in the Southern Hemisphere representing a growing ecological and economic problem in the last decades Blanco & Ector, 2009;Bray, 2014). Though both native and invasive bloom-forming genotypes of D. geminata prefer oligotrophic waters, the latter ecotype is positively correlated with secondary nutrients as Ca + and SO 4 2− ions (Lindstrøm & Skulberg 2008;Whitton et al., 2009;Rost et al., 2011). ...
Both natural and anthropogenic processes can lead to the increasing salinity of surface waters. The knowledge about the ecological consequences of salinization on the biota is limited especially in case of microbiota, like diatoms. We collected the existing knowledge about the relationship between salinity and diatoms in fresh and saline waters. Based on the available papers, conductivity and ion composition are the most important variables shaping diatom communities. Secondary salinization can mask regional differences in diatom assemblages. Trait-based analyses highlight the competitive advantages of motile guild and the extreme trait categories in these environments. The increasing conductivity along a wide conductivity scale decreases the alpha-diversity. Salinization induces the spread and invasion of marine and brackish species into inland freshwaters as well as that of freshwater species tolerating elevated conductivity and/or need specific ions. Concerning food webs, salinity can directly change diatom communities and the subsequent upper trophic levels but most likely this effect manifests as a top-down regulation. Applicable diatom indices are available to assess the level of salinization. Furthermore, diatom-inferred salinity reconstructions are widely applied to assess the past changes of salinity. However, future models predicting ecological consequences of salinization are scarce and sometimes contradictory.
... Their massive biomass can lead to the disruption of the food web in the area, reducing the habitats of several groups of organisms (e.g. aquatic macroinvertebrates, fishes) and endangering the biodiversity of the communities living there (Bray, 2014). It results in significant and even drastic changes in ecosystems leading to changes in ecosystem functioning, trophic interaction and habitats Sala et al., 2000;Bray, 2014 (Laing and Gollasch, 2002;Bothwell et al., 2014;Novis et al., 2017;Rodríguez et al, 2017;Ahmmed et al., 2021;Kilroy et al., 2021;Kato-Unoki et al., 2022). ...
... aquatic macroinvertebrates, fishes) and endangering the biodiversity of the communities living there (Bray, 2014). It results in significant and even drastic changes in ecosystems leading to changes in ecosystem functioning, trophic interaction and habitats Sala et al., 2000;Bray, 2014 (Laing and Gollasch, 2002;Bothwell et al., 2014;Novis et al., 2017;Rodríguez et al, 2017;Ahmmed et al., 2021;Kilroy et al., 2021;Kato-Unoki et al., 2022). Microalgae cultures used for biofuel production, carbondioxide capture and for the production of high value products are also threatened by invasive diatom species (e.g. ...
... The knowledge of biodiversity of aquatic and subterranean biota, invertebrates or microorganisms including algae is underrepresented (MEA, 2003). Most processes, whether human-induced or of natural origin that contribute to the biodiversity loss in terrestrial areas or in macroscopic communities also affect microorganisms with diatoms among them (MEA, 2005;Bray, 2014;Reid et al., 2019). Their assemblages are directly impacted by many of the threats listed by Reid et al. (2019) including changing climate Várbíró et al., 2020;Tornés et al., 2021;B-Béres et al., 2019B-Béres et al., , 2022, biological invasions (Kato-Unoki et al., 2022;Kilroy et al., 2021), harmful algal blooms , emerging contaminants (Smucker & Vis, 2009), microplastic pollution (Harrison et al., 2012), freshwater salinization (Potapova & Charles, 2003) and cumulative stressors. ...
Diatoms, a unique group of algae colonising a wide range of aquatic habitats and contributing to human well-being in many ways. We list and summarise these services using the classification of the Millennium Ecosystem Assessment (MEA), i.e. supporting, regulating, provisioning and cultural services. The most relevant supporting services are photosynthesis and primary production, as well as sediment formation. They also play a key role in nutrient cycling and habitat provisioning and serve as food for many organisms. Regulating services as oxygen production, climate control or sediment stabilisation are difficult to discuss without diatoms. Many provisioning services, directly used by humans, can be obtained from diatoms. These are tangible products such as medicines and immunostimulants but direct technologies such as wastewater treatment, micro- and nanotechnologies were also developed using diatoms. Studying of the past, present, and future linked to diatoms as a tool for palaeolimnology, ecological status assessment of waters and climate modelling is essential. Finally, the impressive morphology and ornaments of diatom frustules make them one of the most spectacular microorganisms, inspiring artists or providing a number of educational opportunities. Therefore, protecting aquatic habitats they inhabit is not simply a nature conservation issue but the key for human well-being in the future.
... The colonial benthic diatom Didymosphenia geminata (Lyngbye) M. Schmidt is capable of producing EPS stalk material that can result in dense macroscopic growths on the river bottom . Unlike most algal blooms which result from a proliferation of cells (Smayda, 1997), stalk material dominates D. geminata blooms, making up greater than 99% of the biomass of some blooms (Bray, 2014). Blooms often occur in rivers with very low soluble reactive phosphorus (SRP) concentrations , at or below the concentration detectable by many analytical techniques. ...
Despite two decades of research, the cause of blooms of the diatom Didymosphenia geminata remains uncertain. Blooms have been associated with low nutrient, oligotrophic streams. In this study, we used available data from across the globe and conducted experiments to determine how D. geminata responds to soluble reactive phosphorus (SRP) concentrations. Globally, D. geminata blooms have been found in streams with SRP below 11 μg P l−1. In North America, blooms only occurred at high equivalent latitudes when SRP was very low, whereas at lower latitudes blooms were observed under higher SRP concentrations. Using an in situ experiment, we found that following physical removal of D. geminata from stones, regrowth did not occur despite low SRP concentrations. In a second experiment, we found that there were no differences in D. geminata growth between a treatment which depleted SRP and a treatment which maintained elevated springtime SRP levels. These findings indicate that D. geminata blooms do not always form when SRP is low, even when cells are present. Bloom formation that is not exclusively related to low SRP suggests additional chemical or biotic factors, specific physical conditions, a seasonal timing requirement, or some combination of these with low P that are necessary to produce blooms.
... Our findings agree with the stalk formation patterns of Didymosphenia geminata, which blooms in oligotrophic rivers, and stalk overproduction was clearly related with water's P-depleted conditions Bothwell, 2011, 2012). These proliferations consist mainly in stalk material (Bray, 2014), which has been interpreted as an adaptive mechanism to maximise phosphate supply in chronic phosphorus-limited environments (Bray et al., 2017). In this species, phosphatase activity has been localised on or within stalks (Ellwood and Whitton, 2007;Aboal et al., 2012). ...
... The structure of the stalks of L. colosalis (Fig. 1e) and D. geminata (Aboal et al., 2012) seem similar, but a more in-depth microscopic study is needed. In both species a high percentage of mucilaginous mass consisted in stalk material (Bray, 2014) (Fig. 3c and d). It is quite likely that L. colosalis stalks could also play a significant role in adaptation to marine coastal systems with a high N:P stoichiometry of water and even in alkaline phosphatase activity but further research is needed to confirm these hypothesis. ...
... It forms blooms in oligotrophic rivers, where it has been proven that stalks overproduction is linked to the growth P-depleted conditions of overlying waters Kilroy & Bothwell, 2012). This proliferation consists mainly in stalk material (Bray, 2014), which has been interpreted as an adaptation mechanism to maximise the phosphate supply under chronic phosphorus-limited environments (Bray et al., 2017). In this species, phosphatase activity has been localised on or within stalks (Ellwood & Whitton, 2007;Aboal et al., 2012) by means of cells that can uptake organic phosphate; e.g. from the surrounding mucilage matrix. ...
... Proliferations of the invasive diatom Didymosphenia geminata (Bacillariophyceae) substantially alter periphyton biomass, affecting habitat characteristics and algal, invertebrate and fish community structure ( Figure 1a; Gillis & Chalifour, 2009;Kilroy, Larned, & Biggs, 2009;Jellyman & Harding, 2013;Bray, 2014). Didymosphenia geminata blooms are increasing in their severity and extent causing concern in many temperate regions of Europe, North and South America, Asia and Australasia (Beltrami et al., 2008;Bothwell, Taylor, & Kilroy, 2014;Spaulding & Elwell, 2007). ...
... Didymosphenia geminata challenges conventional understanding of periphyton accrual, where phosphorus limitation coupled with high light conditions drives basal stalk production and results in proliferation development . This mechanism produces dense benthic mats that are up to 99% stalk material by biovolume and have biomass orders of magnitude greater than proliferations of most other freshwater algae (Bray, 2014;Cullis, Gillis, Bothwell, & Kilroy, 2012). Stalk material exuded from a basal pore field (Metzeltin & Lange-Bertalot, 1995) comprises polysaccharide (Gretz, 2008). ...
... 2-4 lg/L). At phosphorus concentrations above 2 lg/L DRP D. geminata is less likely to bloom and, where present, often persists only as a minor component of periphyton (Beltrami et al., 2008;Bothwell et al., 2014;Bray, 2014;Kilroy & Larned, 2016). Disappearance of D. geminata has also been recorded from rivers with increasing nutrient concentrations (Kawecka, 1965;Kawecka & Sanecki, 2003). ...
Nuisance proliferations of the invasive benthic alga Didymosphenia geminata (Bacillariophyceae) are of major concern in many temperate regions due to their severe effects on river habitats and communities. Proliferations result from the production of basal stalk material, stimulated by phosphorus limited, high light conditions. An unresolved disconnect occurs where nitrogen and phosphorus are observed to stimulate D. geminata cell division, but, within a realised niche, disappearance or establishment failure occurs where dissolved reactive phosphorus ( DRP ) concentrations occur above c . 2–5 μg/L.
Our aims were to examine the mechanisms behind D. geminata bloom stimulation and absence/disappearance. We examined: (1a) whether prolonged nitrogen (Na NO 3 – N) and phosphorus (NaH 2 PO 4 – P) addition would stimulate cell division, and (1b) whether subsequent nutrient limitation stimulated stalk production; (2) whether the mechanism behind D. geminata absence at >5 μg/L DRP , occurred either as (2a) a deleterious consequence of prolonged N + P exposure or (2b) was associated with increasing densities of co‐occurring algae; and (3) whether water velocity stimulated D. geminata cell division thereby influencing outcomes.
Didymosphenia geminata cell densities, frequencies of dividing cells, stalk production and densities of competing algae were examined in flow‐through channel mesocosms over 8 weeks. Treatments included: Waitaki River water (control); N + P amended water; and two treatments in which nutrient amendments were changed over time, these being N + P to N, and N + P to Waitaki water.
Continued N + P amendment was positively correlated with D. geminata cell densities. N‐replete P‐limited channels, however, accrued greatest densities of D. geminata cells, stalk fragments and dividing cells. Results suggest that within a realised niche short term N + P amendment followed by chronic P limitation could either hasten and/or worsen bloom development.
Water velocity influenced community successional trajectories and D. geminata fitness outcomes. Across all nutrient and velocity treatments, a decline in D. geminata cell densities and cell division was correlated with increasing densities of competing algae.
Phosphorus limitation stimulating stalk production appears to be an example of physiological stress resulting in increased fitness (known as eustress) and D. geminata dominance. This contrasts with a general pattern of competitive exclusion as nutrient concentrations increase.
... Under hydrologically stable conditions, this can result in large benthic masses . Proliferations consist of up to 99% stalk material, cover entire stream reaches and may be over 300 mm in thickness (Bray, 2014). These mats are a complex mixture of detritus, bacteria, macroinvertebrates and mesofauna, epiphytic algae, and other unattached algal species (Gretz, 2008). ...
... Ellwood & Whitton (2007) found organic phosphorus to comprise *85% of filterable phosphate in the water column, over an 8-month period within a system containing D. geminata proliferations. While water column concentrations of organic phosphorus may be important in providing D. geminata with P sources, data suggest that water column DRP, TP, OP and FOP are limiting, and rarely above detection limits in New Zealand rivers with D. geminata proliferations Bray, 2014). Moreover, organic phosphorus, bioavailable and larger detrital material were all present within mat interstices at concentrations orders of magnitude greater than overlying water, corroborating observations and analyses elsewhere (Kirkwood et al., 2007;Gretz, 2008;Aboal et al., 2012;Kilroy pers. ...
... Novel or quantitative differences in traits associated with resource use efficiency, or rates of acquisition are known to be adaptive strategies of invaders of nutrient-poor systems (Funk & Vitousek, 2007;Leishman et al., 2010;Heberling & Fridley, 2013;Ordonez & Olff, 2013). Increasing fitness with the increasing biomass is observed in D. geminata in which both downstream propagule numbers and benthic cell density positively correlate with biomass upstream (Bray, 2014). The importance of phosphatase acquisition and nutrient cycling within a mat will vary dependent on available water column phosphate (organic and inorganic), organic matter accrual through both allochthonous and autochthonous pathways, and with mat depth and age. ...
Didymosphenia geminata is a benthic bloom-forming diatom that is invasive in many temperate, oligotrophic freshwater ecosystems. D. geminata blooms are unusual, resulting from prolific basal stalk production stimulated by phosphorus limitation. The adaptive value of stalk production and bloom development is disputed. We examined blooms in relation to stalk biomass, biovolume and phosphatase activity. An austral summer survey of 15 sites within the Waitaki River of New Zealand compared reference communities (no detectable D. geminata), with those impacted by high and low D. geminata biomass. Sites were compared for differences in phosphatase location and activity using chromogenic substrates, community composition using morphological identifications, and overlying water and pore-water chemistry. Experimental microcosms subjected live proliferations to varied phosphate concentrations, and phosphatase rates and location were examined. Survey results identified phosphatase activity increased with D. geminata biomass, with lowest rates in reference communities. Pools of labile nutrients were detected in D. geminata mats, and in vitro hydrolysis rates were rapid in replete phosphoester conditions (~0.2 mmol l−1 h−1 cm−2 at 16°C), with activity concentrated on stalks. Our results suggest D. geminata bloom development is an adaptation to maximise supply of phosphate under chronic phosphorus limitation.
... Kilroy & Bothwell (2011) proposed that under these phosphorus-limiting conditions, D. geminata cells divide slowly, but photosynthesis continues and excessive stalks are produced as a form of 'photosynthetic overflow'. Other field-based studies or assessments have highlighted stable river flows, temperature, light and various elements (e.g., calcium) as playing a role in regulating mat development (e.g., Lindstrøm & Skulberg 2008, Kirkwood et al. 2009, Kilroy & Bothwell 2012, Bray 2014. Despite the results of these and other studies, multiple factors related to D. geminata biology and mat formation remain unknown, including variables that initiate cell attachment, triggers of sexual reproduction and cellular mechanisms that promote excessive stalk production. ...
... The results of both PAM and microscopical assessments in the media manipulation experiments showed that D. geminata could only survive within a narrow range of low NaNO 3 concentrations. In an extensive field-based study, Bray (2014) identified flow regulation, river stability and lower nitrogen and magnesium concentrations as the main determinants of D. geminata presence or increased biomass. Other evidence to suggest a role of nitrogen in regulating D. geminata comes from research on spring-fed creeks. ...
Over the past three decades the freshwater diatom Didymosphenia geminata (Lyngbye) M. Schmidt has expanded its range globally. In some rivers D. geminata has become invasive, forming expansive and thick polysaccharide-dominated mats. Techniques to maintain and study D. geminata in the laboratory are limited. In this study, a 96-well plate format assay using pulse amplitude modulated (PAM) fluorometry was developed to study D. geminata under controlled conditions. The PAM assay and morphological assessments were used to investigate the addition of sodium nitrate (NaNO3) to a previously developed D. geminata-specific growth medium (Didymo Medium; DM). Addition of low concentrations (ca. 0.003–0.018 µM) enhanced cell survival and health. Central-composite design (CCD) experiments coupled with response surface methodology were then used to investigate optimal concentrations of six key chemicals in DM (magnesium sulphate, calcium chloride, mono-potassium phosphate, sodium metasilicate pentahydrate, ferric sodium ethylenediaminetetraacetic acid (EDTA) and NaNO3). An optimised DM recipe is provided. The PAM assay was also used to analyse the influence of maintaining D. geminata cells in river waters sourced from locations with and without the diatom. A NaNO3 spiking experiment was undertaken using water from one location. The maximum quantum yields of cells maintained in all river waters remained relatively constant and higher than those maintained in DM or Milli-Q water for the seven day test period. The results of the NaNO3 river water spiking experiment provided contrasting results to the culture medium trials, with minimal impact on photosynthetic efficiency. These data, coupled with the results of the CCD experiment, suggest complex interactions among nutrients that have varying effects on D. geminata cell health. Together with microscopical observations, the 96-well plate PAM assay provides a useful tool for improving knowledge of D. geminata biology and growth requirements.
Didymosphenia geminata is a stalked freshwater diatom, which forms large blooms in ultra-oligotrophic conditions, and it has been declared a nuisance species in many lotic systems worldwide. Its presence is verified in Argentine Patagonia since 2010. To understand the differences in the community of macroinvertebrates between non-invaded sites and D. geminata blooms, three non-invaded sites and three sites with 80–90% blooms coverage were sampled seasonally at Futaleufú River. Physical and chemical variables (pH, suspended solids, total dissolved solids, conductivity, dissolved oxygen, and nutrients) showed no significant differences between sites. Sites with D. geminata blooms were associated with significantly higher values of periphyton biomass and chlorophyll a. Macroinvertebrate community differed between D. geminata infected sites and sites with native periphyton. Higher total macroinvertebrate density, higher tolerant groups (Orthocladiinae and non-insect taxa) density, and total richness were found in the presence of blooms. Trophic structure changed at D. geminata blooms, where shredders and collector-gatherers increased in abundance. The diatom blooms may constitute a new complex micro-habitat that provides refuge from harsh current and predators, as well as new foraging opportunities, producing a bottom-up effect on the benthic community.
