The non‐indigenous diatom Didymosphenia geminata alters benthic communities in New Zealand rivers

Abstract

Summary 1. Blooms of the benthic, stalked diatom Didymosphenia geminata were first observed in New Zealand in 2004. Since then, D. geminata has spread to numerous catchments in the South Island and is also spreading in its native range. The species is a rare example of an invasive alga in lotic systems. 2. Ecosystem effects may be expected as D. geminata attains unusually high biomass in rivers. We examined data from three independent studies in three South Island, New Zealand, rivers for evidence of effects on periphyton biomass and benthic invertebrate communities. 3. The combined results confirmed that the presence of D. geminata was associated with greatly increased periphyton biomass and, in most cases, increased invertebrate densities. We also recorded shifts in community composition, dominated by increased densities of Oligochaeta. Chironomidae, Cladocera and Nematoda also generally increased in density with D. geminata. Significant increases or declines in other invertebrate taxa were inconsistent among rivers. 4. In all three studies, increased spatial invertebrate community homogeneity was associated with high D. geminata biomass at the within‐river scale. However, no declines in taxon richness or diversity were detected. 5. Although ecosystem effects of D. geminata on existing periphyton biomass and invertebrate communities are measurable, no inferences can be made from the present data about effects on higher trophic levels (fish).

Invertebrate Composition and Abundance Associated withDidymosphenia geminatain a Montane Stream

“…DISCUSSION Overall, we observed higher abundance of Diptera and a lower percentage of EPT in D. geminata impacted areas of Rapid Creek. Similar results were reported from the White River, Arkansas, USA (Shelby 2006), and several New Zealand rivers (Lamed et al 2007, Shearer et al 2007, Kilroy et al 2009). Kilroy et al (2005) reported an increase of invertebrates overall, particularly for dipterans.…”

“…Recent research has focused primarily on the biology and distribution of D. geminata (Kawecka and Sanecki 2003, Kilroy et al 2005, Kilroy et al 2006, Kirkwood et al 2007, Spaulding and Elwell 2007, Whitton et al 2009). Other recent research on invertebrate communities has shown that invertebrate composition tends to shift from larger taxa (i.e., Ephemeroptera, Plecoptera, Trichoptera) to smaller taxa such as Diptera in areas impacted by D. geminata (Shelby 2006, Shearer et al 2007, Larson and Carreiro 2008, Gillis and Chalifour 2009, Kilroy et al 2009). Moreover, total invertebrate abundance tends to increase in areas where D. geminata is present (Gillis andChalifour 2009, Kilroy et al 2009).…”

Molecular species discovery in the diatom Sellaphora and its congruence with mating trials.

“…Most S. auldreekie clones have been isolated from Scottish lochs, but a single S. auldreekie strain, Cr44, was isolated from Australia, and S. capitata and S. bisexualis have also been found in both the UK and Australia Mann et al 2009). The extent to which humanmediated introductions have altered the geographical distribution of Sellaphora species remains unknown, but numerous cases of invasive aquatic species are known in Australasia, including some microalgae (Harper 1994;Wells et al 1999;Kilroy et al 2009). New sequencing technologies applied directly to natural samples or community fingerprinting techniques in combination with a DNA barcode database for species identification might in the future be used to tackle the ecology and geographical distribution of these species.…”

Molecular genetic tools for environmental monitoring of New Zealand's aquatic habitats, past, present and the future

“…Over the last two decades there has been a worldwide increase in the distribution and severity of blooms of D. geminata. This species has a unique ability to secrete unprecedented masses of mucilaginous stalks which forms mats that can severely impact native species and ecosystem functioning (Kilroy et al 2009 ) is recommended for collecting river samples for this QPCR assay and during a field trial positive results were obtained for samples with c. 60 cell m …”