An ecologically and economically disruptive harmful algal bloom (HAB) affected much of the northeast Pacific margin in 2015, during a prolonged oceanic warm anomaly. Caused by diatoms of the genus Pseudo‐nitzschia, this HAB produced the highest particulate concentrations of the biotoxin domoic acid (DA) ever recorded in Monterey Bay, California. Bloom inception followed strong upwelling during the spring transition, which introduced nutrients and eliminated the warm anomaly locally. Subsequently, moderate and intermittent upwelling created favorable conditions for growth and accumulation of HAB biomass, which was dominated by a highly toxigenic species, P. australis. High cellular DA concentrations were associated with available nitrogen for DA synthesis coincident with silicate exhaustion. This nutrient influence resulted from two factors: (1) disproportionate depletion of silicate in upwelling source waters during the warm anomaly, the most severe depletion observed in 24 years, and (2) silicate uptake by the dense diatom bloom.

The field of eDNA is growing exponentially in response to the need for detecting rare and invasive species for management and conservation decisions. Developing technologies and standard protocols within the biosecurity sector must address myriad challenges associated with marine environments, including salinity, temperature, advective and deposition processes, hydrochemistry and pH, and contaminating agents. These approaches must also provide a robust framework that meets the need for biosecurity management decisions regarding threats to human health, environmental resources, and economic interests, especially in areas with limited clean-laboratory resources and experienced personnel. This contribution aims to facilitate dialogue and innovation within this sector by reviewing current approaches for sample collection, post-sampling capture and concentration of eDNA, preservation, and extraction, all through a biosecurity monitoring lens.

Domoic acid (DA) is produced by almost half of the species belonging to the diatom genus Pseudo-nitzschia and causes amnesic shellfish poisoning (ASP). It is, therefore, important to investigate the diversity and toxin production of Pseudo-nitzschia species for ASP risk assessments. Between 2018 and 2020, seawater samples were collected from various sites around Aotearoa New Zealand, and 130 clonal isolates of Pseudo-nitzschia were established. Molecular phylogenetic analysis of partial large subunit ribosomal DNA and/or internal transcribed spacer regions revealed that the isolates were divided into 14 species (Pseudo-nitzschia americana, Pseudo-nitzschia arenysensis, Pseudo-nitzschia australis, Pseudo-nitzschia calliantha, Pseudo-nitzschia cuspidata, Pseudo-nitzschia delicatissima, Pseudo-nitzschia fraudulenta, Pseudo-nitzschia galaxiae, Pseudo-nitzschia hasleana, Pseudo-nitzschia multiseries, Pseudo-nitzschia multistriata, Pseudo-nitzschia plurisecta, Pseudo-nitzschia pungens, and Pseudo-nitzschia cf. subpacifica). The P. delicatissima and P. hasleana strains were further divided into two clades/subclades (I and II). Liquid chromatography-tandem mass spectrometry was used to assess the production of DA and DA isomers by 73 representative strains. The analyses revealed that two (P. australis and P. multiseries) of the 14 species produced DA as a primary analogue, along with several DA isomers. This study is the first geographical distribution record of P. arenysensis, P.cuspidata, P. galaxiae, and P. hasleana in New Zealand coastal waters.

Following the recent leap in biotechnologies and particularly in high-throughput sequencing techniques, environmental DNA and RNA (eDNA and eRNA) are increasingly being used for biodiversity assessments and monitoring of complex ecosystems – lakes, streams and coastal waters. Growing interest and affordability of eDNA/eRNA based tools have led to the emergence of manifold protocols for capturing genetic material from variable biological matrices, e.g. soil, water, feces, biofilms, etc. The variability in eDNA and eRNA material (ranging from free-floating molecules to cellular complexes to intact organisms) and its patchy distribution in the environment may substantially affect effective capture from the environment. Therefore, it is extremely challenging for stakeholders to standardize or choose optimal protocols, impeding incorporation of eDNA/eRNA methods into routine monitoring and surveillance programs. Although there is still no consensus on the standardized workflow for processing eDNA/eRNA samples, the common practice for water samples is to concentrate nucleic acids (NA) via filtration, ranging from 0.22 to 20-micron pore size. Although using the smallest pore is assumed efficient for NA capture from a wide range of material (including sub-cellular particles), a trade-off between detection of the meaningful molecular signal and time(cost)-efficiency is needed. Using finer pore membranes increases the likelihood of clogging and prohibits processing larger volumes of water, thus reducing the chances of detecting rare biodiversity. Moreover, large sample volumes may be accompanied by increased concentrations of inhibitory substances (e.g. humic compounds), suppressing target molecular signal. Comparative studies involving formal cost-efficiency assessments are lacking, restricting informed decision-making around the optimized sampling approach for addressing a particular research or surveillance question. Identifying the optimal combination of time effort and signal detection efficiency is particularly crucial for targeted surveillance, e.g. detection and monitoring of nuisance organisms, endangered and indicator taxa or other species of particular economic or cultural importance. Although it has been previously shown that larger pore filters can be as efficient for species detection from waterborne eDNA, more data are needed on the amount and type of NA material capture and loss. Here, we present a comparison study using an easily cultured microalgal species (Alexandrium pacificum) as a proxy to test the effectiveness of different filter membranes (cellulose acetate membranes of 5 μm, 1.2 μm or 0.45 μm pore size, and positively charged nylon membrane with 1.2 μm pore size) in the context of targeted species detection. We performed an efficiency analysis to identify the method that delivered the optimal use of resources. A tiered experimental design was applied to: i) assess the impact of membranes on capturing various fractions of target eDNA/eRNA (intact cells, partially lysed cells, naked NAs) spiked into pre-filtered and ambient environmental seawater and ii) establish efficiency and utility of different membranes in terms of optimizing the performance – maximized output (capture of target eDNA and eRNA) balanced against minimized time and cost input. The results showed no statistically significant difference between membranes for capturing DNA signal from intact and partially lysed cell treatments. However, positively charged nylon membranes were more efficient in capturing naked NAs, as well as RNA from partially lysed cells. In terms of time effort and volume processed, higher efficacy was reported for the larger pore size cellulose membranes. However positively charged nylon consistently performed better for capturing RNA signal across treatments.