Work

Alexandrium catenella blooms driven by extreme thermal anomalies in a fjord system

Year: 2026

Type: article

Abstract: Blooms of Alexandrium catenella have affected coastal activities of the Northwestern Patagonia in the last 30-years, more particularly shellfish aquaculture, benthic fisheries and public health. These blooms have been associated with large-scale climatic anomalies such as positive phases of the El Niño Southern Oscillation (ENSO) and Southern Annular Mode (SAM). Nevertheless, their association with large-scale oceanographic anomalous conditions has been little studied. Here, we carried out for the first time a retrospective co-occurrence analysis of A. catenella blooms and Marine Heatwaves (MHWs), defined as anomalously warm temperature events observed in the ocean, over the 20 years period 2003–2023 in the Northwestern Patagonia. Our results reveal the important role of positive temperature anomalies and therefore MHWs in facilitating A. catenella blooms. Summers 2009, 2016, and 2018 stand out in terms of bloom intensities and MHWs, registering cell densities above 50 × 10 3 cells L −1 and the highest values were found in March 2009 with 3.4 × 10 5 cells L −1 . These strong blooms were accompanied by strong temperature anomalies and MHWs, with events classified as Category III in 2009 and Category II in 2016. In contrast, low cell densities of A. catenella were detected in summer 2019 and 2020, attributed to unfavourable thermal conditions (either unstable or not strong enough), limiting the bloom proliferation. Overall, our results indicate that positive thermal anomalies and MHWs create favourable conditions for the initiation and intensification of A. catenella blooms in Northwestern Patagonia, although thermal forcing alone is not always sufficient to trigger bloom development.

Source: Water Biology and Security

DOI: 10.1016/j.watbs.2026.100718

Authors: Cécile Pujol, Patricio A. Díaz, Guido Mancilla-Gutiérrez, Felipe Tucca, Alexander Barth, Aida Alvera-Azcárate