Work

Detection of the Toxic Marine Dinoflagellate Alexandrium pseudogonyaulax in Small-Volume Seawater Samples Using a ddPCR Assay for Environmental DNA at the Southern Baltic Sea Coast

Year: 2026

Type: article

Abstract: Alexandrium pseudogonyaulax is an increasingly recurrent harmful algal bloom species in Northern European waters, making reliable detection, including of low-abundance populations, important for monitoring. This study evaluated droplet digital PCR (ddPCR) for detecting A. pseudogonyaulax in a standardised 1-L seawater sample and compared molecular measurements with microscopic cell enumeration. Weekly surface-water samples were collected at Heiligendamm, southern Baltic Sea, from June to September 2021 (18 samples). Environmental DNA was extracted after filtration of 1 L of seawater, and A. pseudogonyaulax 28S rRNA gene copy numbers (GCN) were quantified by ddPCR. Microscopic enumeration was performed from a 25-mL subsample, corresponding to an approximate detection limit of 40 cells L−1. Molecular and microscopic measurements showed pronounced temporal co-variation. Across the time series, 28S GCN ranged from 3.8 × 103 to 9.93 × 106 GCN L−1. On five sampling dates, microscopy was below its detection limit, whereas A. pseudogonyaulax DNA was consistently detected at 3.8 × 103–3.19 × 105 GCN L−1. Among samples with microscopically detectable cells, GCN and cell abundance showed a positive but non-significant association (Spearman’s ρ = 0.58, p = 0.077, n = 10). Field-derived GCN-per-cell estimates were lower than culture-derived values, indicating that a fixed conversion factor should not be applied to environmental samples. Overall, the results support ddPCR as a sensitive complement to microscopy and indicate that a standardised 1-L sample can support species-specific detection also at low abundance. Further validation across sites, seasons, and molecular targets is required before routine implementation.

Source: Water

DOI: 10.3390/w18212689

Authors: Gizem Koc, Anke Kremp, Philipp Retzlaff, Urban Tillmann, Bernd Krock, Matthias Labrenz

Institutions: Leibniz Institute for Baltic Sea Research Warnemünde, Klaipėda University, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung

Language: English

Topic: Marine Toxins and Detection Methods

Subfield: Environmental Chemistry

Field: Environmental Science

Domain: Physical Sciences

SDGs: Life below water, Clean water and sanitation

Open Access status: gold

Estimated APC paid: $3,137