An overview of the 20182025 monitoring, detection, and control programme for Alexandrium catenella in Southern Chile The frequency, persistence, and geographical extent of harmful algal blooms (HABs) caused by the dinoflagellate Alexandrium catenella have increased in southern Chile over recent decades, largely in association with climate-change-related environmental anomalies [1]. This species produces paralytic shellfish toxins (PST), causing paralytic shellfish poisoning (PSP) and generating significant impacts on public health and the fisheries and aquaculture sectors. Of particular concern is its documented northward expansion towards areas with intensive aquaculture [23], where high densities of vegetative cells may cause substantial mortality in farmed fish [4]. The threat became particularly evident during the austral summer of 2016, when anomalous oceanographic conditions associated with a strong El Niño event and the positive phase of the Southern Annular Mode [5] contributed to the simultaneous development of extensive blooms of Pseudochattonella verruculosa and A. catenella. This event caused one of the largest socio-economic impacts associated with HABs worldwide [68]. The massive expansion of A. catenella around Chiloé Island led to extreme shellfish toxicity and one of the most severe socio-environmental crises in Chilean history [911]. In response, the National Fisheries and Aquaculture Service (SERNAPESCA) established a monitoring, detection, and control programme for A. catenella under Res. Ex. N 529/2009 and subsequent amendments, most recently Res. Ex. N 6004/2019. Since 2021, the programme has been implemented by the Universidad San Sebastián in Puerto Montt. Its objective is to prevent the northward transport of A. catenella from bloom-affected areas, such as Aysén, into regions where the species is absent or occurs at low abundance. Wellboats transporting live salmon from the southernmost provinces (Magallanes and Aysén) northward pose a risk of introduction of harmful algal species into new growing areas. These vessels, predominantly used in modern Fig. 1. Schematic representation of the wellboat sampling process, conducted by qualified professionals acting as legal witnesses who certify that A. catenella has not been detected in the live fish cargo from phytoplankton sample collection (1) to the reporting of results to SERNAPESCA and the company responsible for salmon production and transport [4]. In the event of a positive detection, regulations require the wellboat to fully recirculate the water in its holds under closed-circuit conditions south of the 433453S latitude. HARMFUL ALGAE NEWS NO. 84 / 2026 salmon aquaculture, are specialized vessels equipped with large circulating seawater tanks (wells) designed to hold and transport live fish. In compliance with national regulations, SERNAPESCA requires phytoplankton screening of all wellboat water transporting live salmon northward across the 4322S sanitary boundary, also known as the HABline, towards the Los Lagos region, where major salmon processing plants are located (Fig. 1). To this aim, samples for HAB screening are collected each time the water in the salmon wells is renewed. At each sampling point, 20 L of well water are sieved through a 20-μm mesh, and the plankton concentrate, resuspended in 60 mL, is poured into a 500 mL bottle, fixed with Lugols iodine, and left to settle for 10 min. Then, an aliquot is taken with a pipette from the bottom of the bottle, and a drop (0.1 mL) is placed on a glass slide, covered with coverslip, and scanned under an onboard microscope. This operation is repeated three times. The wellboat is confirmed to be A. catenella-free when no cells are detected in any of the three aliquots examined. When A. catenella is detected, vessels must undergo additional phytoplankton analysis before receiving authorisation to continue their journey. Surveillance is complemented by weekly monitoring at four fixed coastal stations along the sanitary boundary. From 2018 to 2025, the programme analysed 24,851 samples, of which 248 (1%) were positive for A. catenella. These findings demonstrate the continuity of the monitoring effort and its capacity to provide timely detection of this microalga during live salmon transport operations. The highest number of detections occurred in 2018, when 168 of 2,797 samples (6%) were positive (Fig. 2). This increase coincided with a bloom of A. catenella in the Aysén Region which reached maximal densities of 50,000 cells L-1 (Fig. 3), highlighting the importance of continuous surveillance to prevent the spread of this highly toxic species into unaffected areas. Overall, the A. catenella programme has strengthened early warning and con- 9 Harmful Algae News An IOC Newsletter on Toxic Algae and Algal Blooms No. 84 September 2026 https://hab.ioc-unesco.org/ Unveiling biotic controls of Alexandrium minutum in the Ría de Vigo (NW Spain) Understanding biotic interactions that regulate the dynamics of harmful algal bloom (HAB) species r Fig. 2. The study area in the Ría de Vigo (NW Spain). The red dots indicate the locations where the A. minutum strains were isolated. [1]. We propose that such stable abiotic conditions may facilitate the establishment and persistence of key biotic interactions between the microalgae and their micr Fig. 4. Abundance of Alexandrium minutum (Am) (A) and bacteria (B) in quasi-axenic monocultures (blue lines) or co-cultures with Alteromonas sp. (Alt) (red lines) with B-vitamins (w B-vit, solid lines) or without B-vitamins (wo B-vit, dashed lines). (C) Taxonomic composition of the bacterial microbi Fig. 5. Box and whisker plot showing the response ratios (RR) of Alexandrium minutum growth to the addition of different Zostera marina exudates at low (200300 μM DOC) and high (500600 μM DOC) concentrations. A total of 14 and 10 response ratios were included for the low and high concentration treat dinoflagellates. It has been suggested that phenolic compounds produced by marine angiosperms, e.g. [25], may play a significant role in the negative interaction between these plants and dinoflagellate growth [56, 21]. However, this hypothesis has not yet been experimentally tested. Acknowledgement Intense algal bloom during the austral summer in Inglesa and Calderilla Bays (Atacama, Chile): phytoplankton monitoring, environmental observations and implications for coastal aquaculture Fig. 1. Seawater discoloration in Inglesa Bay sector, Caldera during the first week of February 2026. (A) and Fig. 3. Dominant dinoflagellate species in the algal bloom. (A) Akashiwo sanguinea and (B) Tripos cf. furca. radically (2005, 2009, 2014, and 2016), including blooms of the toxic dinoflagellate species such as Protoceratium reticulatum, which produces yessotoxins (YTX) and has been detected along t Fig. 5. Abundance of other microplankton groups in February 2026 at the five sampling stations in the Caldera Bay System. 2. Rodríguez L 1978. Noticiario Mensual del Museo de Historia Natural de Chile 22(266):69 3. Rodríguez L 1985. Rev Biol Mar 21:173197. https://hdl.handle. net/20.500.14330/PER01 An overview of the 20182025 monitoring, detection, and control programme for Alexandrium catenella in Southern Chile The frequency, persistence, and geographical extent of harmful algal blooms (HABs) caused by the dinoflagellate Alexandrium catenella have increased in southern Chile over recent deca 3. 4. 5. 6. 7. 8. Fig. 2. Annual number of analysed samples and positive detections between 2018 and 2025. Bars represent the total number of samples collected each year. The red area indicates positive results (number shown at the base of each bar), whereas the blue area corresponds to negative res A mixed bloom of Prorocentrum lima species complex and Aphanocapsa sp. under hypersaline conditions in a mangrove lagoon of the Seaflower Biosphere Reserve, Colombian Caribbean Fig. 1. Old Point Regional Park, San Andrés Island, Seaflower Biosphere Reserve, showing the small mangrove lagoon where t Table 1. Measurements of physicochemical characteristics recorded during the mixed bloom of the Prorocentrum lima species complex and Aphanocapsa sp. Old Point, Colombia Lago delle Nazioni, Italy Paracas Bay, Peru 14 April 2026 December 2019 January 2020 2729 August 2017 4.5 106 4.7 107 2 morphological and molecular identification of benthic Prorocentrum and cyanobacteria with measurements of dissolved inorganic nutrients, dissolved and particulate organic carbon, phycotoxins, microbial community composition, sediment resuspension, and water-exchange and salinity dynamics. Acknowled Forthcoming IOC-FAO IPHAB The Eighteenth Session of the IOC-FAO Intergovernmental Panel on Harmful Algal Blooms (IPHAB-XVIII) will meet on 16-18 March 2027 at FAO Headquarters in Rome. The establishment of an intergovernmental panel on HABs in 1991 was a response to the need to improve the manageria The second International Conference on Ostreopsis Development ICOD 2, French Basque Country, June 1011, 2027 Over the last decades increasing attention has been paid to benthic dinoflagellates belonging to the genus Ostreopsis. The presence of these microalgae has been reported in many temperate re NEW! IOC Toxins database The IOC Toxins database is now on-line. It contains reference information about toxins, some of which are associated with Harmful Algal Events. The IOC Toxin Reference List is work in progress. Some sections are complete, some are partly complete and some are empty. The Lis