Biology subjects

Nodder, S.

Publications and source records attributed to Nodder, S..

3 recordsLinked to original sources

bioRxiv2025

Development and validation of five native Aotearoa New Zealand genera-specific large brown macroalgal eDNA ddPCR assays

Environmental DNA is a rapidly growing methodology for ecological studies, leading to an increase in innovative techniques, such as the droplet-digital PCR (ddPCR), that can quantify and target DNA at a high rate of sensitivity for eDNA studies. Large brown macroalgae, Phaeophyceae, are an ecologically significant, diverse, and abundant benthic group in temperate-reef coastal environments. Members of Phaeophyceae, such as Laminariales and Fucales, are becoming recognized as potential significant contributors to Blue Carbon, although measurement of their contribution is challenging. The goal of the present study was to track the fate of specific large, brown macroalgae (kelp) genera detritus, by designing and validating five assays targeting the eDNA of kelp genera that are abundant in the coastal environments of Aotearoa New Zealand: Carpophyllum, Cystophora, Ecklonia, Lessonia, and Macrocystis. Short, diagnostic sequences of the mitochondrial cytochrome c oxidase subunit III gene (cox3) were targeted using ddPCR analysis. Specificity and sensitivity testing were conducted to validate the design of each assay for future use. All five assays produced no cross-amplification and had limits of detection (LoD) that were less than 1 copy/{micro}l. These novel, highly sensitive assays will be beneficial for future experimental and in situ eDNA studies that focus on any of these indigenous genera.

molecular biology↗

bioRxiv2025

Export dynamics of protists across the southern subtropical frontal zone reveal taxon-specific patterns

Gravitational particle sinking is the main mechanism for carbon export in the biological carbon pump. However, the export dynamics of the particle-associated protist community are not fully understood. We used 18S rRNA gene metabarcoding to characterise the exported protist community within sinking particles and bathypelagic surficial sediments in oligotrophic subtropical and high-nutrient, low-chlorophyll subantarctic waters. Sinking particles were collected with formalin-fixed and preservative-free particle interceptor traps (fixed and live traps, respectively) to identify the community involved in particle export (fixed) and protist loss from remineralisation (live). We paired this with community analysis of the upper and lower water column (mixed layer and below mixed layer to mesopelagic, respectively) to compare the relative sources of exported protists. Amplicon sequences variants (ASVs) from upper water column samples accounted for 2 to 4-fold higher proportion of reads and ASV rich-ness compared to lower water column samples in fixed trap and sediment samples, suggesting low influence of the suspended protist community from the lower water column on export. We further traced the export patterns of upper water column protist taxa by analysing the change in taxa relative abundance across the mixed layer to mesopelagic depths. Export patterns differed between taxa, which is similarly suggested by taxa-specific loss of ASV richness between fixed and live traps, but remained the same across biogeochemically-contrasting water masses. This could imply that the drivers for protist loss during export are related to characteristics consistent across environmental conditions, such as specific microbial interactions or inherent cell properties.

microbiology↗

bioRxiv2022

Salp blooms increase carbon export 5-fold in the Southern Ocean

The Southern Ocean (SO) contributes substantially to the global biological carbon pump (BCP). Salps in the SO, in particular Salpa thompsoni, are keystone grazers that produce large, fast-sinking fecal pellets with high export potential. In a first study of this kind, we conducted Lagrangian experiments to quantify the salp bloom impacts on export pathways by contrasting locations differing in salp bloom presence/absence. We show that blooms increased particle export by ~5-fold, and exported up to 46% of net primary production out of the euphotic zone. BCP efficiency increased from 5% in non-salp areas to up to 28% in salp areas, which is among the highest recorded in the global ocean. Using SO salp abundances from KRILLBASE, we estimate they can consume ~ 13% of regional production, mediating 13-40% of the SO BCP. Consideration in models forecasting the SO BCP is recommended considering long-term increases in SO salp abundances.

ecology↗