ACTNOW at ICHA 2025 (Chile)

At the International Conference on Harmful Algae (ICHA 2025) Keelan Lawlor presented new findings that advance our understanding of harmful algal bloom (HAB) monitoring and demonstrate how integrating molecular and traditional techniques can strengthen long-term biodiversity observation in marine ecosystems.

The presentation, titled “Comparison of Microscopy and Metabarcoding for Long-Term Monitoring of Harmful Algae Taxa in the Western English Channel,” was delivered by researchers from the Marine Biological Association (MBA), in collaboration with the Plymouth Marine Laboratory and the University of Plymouth—all part of the ACTNOW consortium.

Revealing Two Decades of Change in Harmful Algae Communities

Using a unique 20-year dataset from the Western Channel Observatory, the study compared data derived from traditional microscopy with those obtained using metabarcoding techniques. The comparison revealed that harmful algal taxa represent between 0.15–6.8% of total phytoplankton based on microscopy, and 6.7–10% when assessed through molecular data.

While both methods identified Phaeocystis spp. as a dominant taxa in at least one season, the molecular dataset revealed a greater diversity of harmful algae overall. This finding suggests that DNA-based approaches can detect a wider range of species, including rare or morphologically similar taxa that often go unnoticed under the microscope.

Toward Integrated Monitoring Approaches

The results underscore the need for integrated monitoring frameworks that combine both microscopy and molecular methods to ensure accurate, large-scale, and long-term tracking of harmful algal species. Molecular tools offer scalability and sensitivity, while traditional microscopy provides continuity with existing datasets—together, they form a powerful basis for next-generation ecosystem assessments.

This work directly supports ACTNOW’s mission to provide science-based tools and indicators that help European regulators and stakeholders assess the cumulative impacts of multiple stressors on marine biodiversity and ecosystem health.