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 2.7 106 350 251 >10 >10 Salinity 43.6 Brackish 34.0 35.0 Temperature (C) 28.0 Variable 16.0 19.5 pH 8.3 7.8 8.2 Dissolved Oxygen (mg L-1) 0.1 Oversaturated Intense reddish Reddish-brown Parameter Sampling date PLSC (cells L-1) Chl-a (μg L-1) Nitrogen (μg L-1) Color ria, can contribute to reddish or pinkish coloration in hypersaline environments [1]. However, their contribution to the Old Point discoloration remains hypothetical because these microorganisms were not directly identified or quantified during the present event. A population of calanoid copepods was also observed in the samples. Their occurrence indicates that grazers were present during the bloom and could potentially have interacted with the dinoflagellate and cyanobacterium populations. However, the present observations do not allow their grazing impact on Prorocentrum abundance to be quantified. The PLSC is composed of benthic and epiphytic dinoflagellates widely distributed in tropical and subtropical marine environments. Members of the complex are commonly associated with macrophytes, sediments, rocks, coral substrates, and other surfaces, and are among the most frequently reported benthic Prorocentrum taxa [2,3]. The occurrence of high densities in the water sample from the Old Point lagoon is therefore of ecological interest. Because our samples were collected from the water column and no quantitative assessment of benthic or epiphytic populations was undertaken, we cannot determine whether the observed cells originated from active growth in the water column, resuspension from sediments, or detachment from mangrove-associated substrates. Nevertheless, the observation suggests that 12 hypersaline mangrove lagoons may provide suitable conditions for the temporary accumulation of PLSC cells in the water column. The environmental conditions recorded during the event are also relevant to the ecology of P. lima. Experimental studies indicate that members of the complex can tolerate relatively broad salinity ranges, including values approaching 45 PSU, and some strains have been reported from hypersaline mangrove-associated habitats [4]. Thus, the salinity of 43.6 PSU recorded at Old Point is within the upper range reported for P. lima and should not be interpreted as evidence of exceptional physiological tolerance. Rather, the combination of high salinity, restricted water exchange, mangrove-derived organic matter, and high microbial biomass may have contributed to the accumulation of PLSC cells in this shallow lagoon. Because dissolved inorganic nutrients and dissolved or particulate organic carbon were not measured during the event, the relative contribution of nutrient enrichment, organic matter availability, and water exchange remains unresolved. The occurrence of P. lima is relevant from a harmful-algal-bloom perspective. Members of the PLSC are recognized producers of bioactive and phycotoxic compounds, particularly okadaic acid and dinophysistoxins, which are associated with diarrhetic shellfish poisoning (DSP) [3,5]. No toxin analysis was conducted in the present study, and therefore no inference regarding the toxicological status of the Old Point bloom can be made. Importantly, no fish, invertebrate, or other visible organism mortality was observed during the bloom. The simultaneous occurrence of Aphanocapsa sp. is also noteworthy. The cyanobacterial population was abundant and occurred together with the PLSC under strongly hypersaline conditions. Although the present observations do not allow us to establish whether the two populations interacted, their co-occurrence suggests that the bloom was not driven by a single phytoplankton taxon but represented a broader microbial response to the unusual environmental conditions prevailing in the lagoon. The provisional identification of the cyanobacterium as Aphanocapsa sp. should be considered tentative until confirmed using additional morphological and/or molecular evidence. Reddish and pinkish water discolorations have previously been documented in tropical mangrove environments under hypersaline conditions. E.g., pink coloration in mangrove-associated environments in Martinique has been attributed to blooms of the halophilic microalga Dunaliella salina. The Old Point event appears to differ from this phenomenon because a high abundance of the PLSC and Aphanocapsa sp. was observed during the discoloration, while the persistence of reddish coloration after filtration suggests that additional dissolved, colloidal, or submicron microbial components may have contributed to the visual appearance of the water. The event therefore illustrates the complexity of microbial assemblages associated with hypersaline mangrove lagoons. To our knowledge, this observation represents a previously undocumented high-density occurrence of the Prorocentrum lima species complex associated with a hypersaline mangrove lagoon in the Caribbean. The combination of extreme but physiologically plausible salinity, high phytoplankton biomass, reddish water discoloration, very low dissolved oxygen, and the simultaneous occurrence of Aphanocapsa sp. suggests a distinctive microbial bloom under restricted water-exchange conditions. Further monitoring should combine HARMFUL ALGAE NEWS NO. 84 / 2026 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