Didymosphenia geminata (Protista, Bacillariophyceae) invasion, resistance of native periphyton communities, and implications for dispersal and management

Abstract

Historically described as cosmopolitan but rare, the benthic diatom Didymosphenia geminata is now considered a nuisance, bloom-forming and invasive species. In New Zealand, D. geminata was first recorded in 2004 in the lower Waiau River. By winter 2008 it had been identified in 26 major catchments. To investigate invasion success of D. geminata in relation to succession and biomass accumulation of native periphyton communities, we conducted a two-factorial field experiment. Seven successional stages of a native periphyton community (substrate exposure time: 0-49 days) were exposed to two D. geminata propagule concentrations (low and high) for 25 days. D. geminata propagule concentration and successional stage of the native periphyton community significantly affected the invasion success of D. geminata. While D. geminata invasion was low on all substrates that had been exposed to the low D. geminata propagule concentration, there was a unimodal relationship between invasion success and substrate exposure time at the high propagule concentration. D. geminata abundance was low on uncolonised substrates, increased when the native communities were 1-or 2-week-old, and low when the age of the native communities was 4 or more weeks. These results imply that D. geminata is a late successional species that needs some existing structure to anchor to a substrate. Although late successional stages of the native periphyton community displayed partial resistance to D. geminata invasion, trying to keep D. geminata abundances as low as possible appears to be the only way to manage this species at this time. Abbreviations DRPDissolved reactive phosphorus DIN Dissolved inorganic nitrogen DRSi Dissolved reactive silicate

Interactions between the mat‐forming algaDidymosphenia geminataand its hydrodynamic environment

“…[37] Current evidence for a dual nutrient-source strategy in D. geminata is limited to our observations of flow-dependent changes in transport processes within mats, low ambient nutrient-concentrations in D. geminata-dominated rivers, and large quantities of POM within and beneath D. geminata mats (Flöder and Kilroy 2009;Whitton et al 2009). More compelling evidence would include high concentrations of dissolved nutrients and/or high rates of POM remineralization in mat matrices, and demonstration of mass transport-limited nutrient uptake.…”

“…Despite these harsh conditions, D. geminata mats can reach densities >1000 g ash‐free dry weight m − 2 and dominate the benthos in terms of cover and biomass (Kirkwood et al 2007; Miller et al 2009; Kilroy et al 2009). D. geminata mats overgrow and kill native periphyton, and they are efficient traps for seston (Flöder and Kilroy 2009). As a result, mats are often underlain by and impregnated with nutrient‐rich particulate organic matter (POM) (Whitton et al 2009).…”

A conceptual model for the blooming behavior and persistence of the benthic mat‐forming diatomDidymosphenia geminata in oligotrophic streams

“…Currently neither of the upper or lower flow related threshold values are known for quantifying the potential for colonization of the substrate by D. geminata. It has been shown that colonization of D. geminata cells after a disturbance event is indeed influenced by the micro‐topography of the substrate material [ Bergey et al , 2010] and the concentration of new cells arriving from upstream [ Flöder and Kilroy , 2009]. The presence of residual D. geminata mats is therefore also likely to affect the colonization of new cells because of the impact of the mats on the near‐bed hydraulic conditions [ Larned et al , 2011].…”

Recent views on river pollution and diatoms

“…Serra et al (2009) looked at metal accumulation kinetics during biofilms colonization. Two papers about an invasive species (Floder & Kilroy, 2009;Kilroy et al, 2009), Dydimosphaena geminata, studied its colonization process and the evolution of its biomass on various substrates in New Zealand rivers; these studies do not assess the effect of any metal or pesticide, however-they were categorized in this group because of the presence of the same indicative word (colonization) in their abstracts.…”