Fig. 2. Programme for the Advanced International Colloquium and Technical Workshop on fish killing marine algae and their effects. blooms. The WG also decided to revise the classic but outdated Cooperative Research Report [2] on HAB effects on mariculture and marine fisheries published in 1992 for the ICES region. This influential but rather sparse document (only 38 pages) provided a cursory overview of HAB effects on living marine resources primarily fish and shellfish. There were no documented distinctions of fish-killing blooms as a functional group, and little understanding of the proximal mechanisms of fish mortalities. From a monitoring and resource management perspective, resolving an apparently simplistic equation (harmful agal bloom = dead fish) was largely a struggle to identify the causative microalgal species and whether their unknown ichthyotoxins were the primary or exclusive lethal mechanism. Aquaculture salmonids are the major finfish resource at HAB risk (ca. 95% by value) within the ICES region, comprising the North Atlantic including ocean gateways to the Arctic and Northern European marginal seas. Historical and prospective future losses are considered in a heavily capitalized industry with inconsistent reporting procedures 2 and inadequate risk assessment strategies. This salmonid risk situation due to HABs is replicated to a large extent in other economies (e.g., Chile, Pacific Northwest Canada and USA, Atlantic Canada, Tasmania, etc.) but does not fairly represent the global scenario for fish-killing blooms affecting other fish species and artisanal or small-scale fisheries. Establishment of a Term of Reference (ToR) within the ICES WGHABD (Belfast 2013) to address fish-killing blooms and marine mortalities coincided with updates and refinements to HAEDAT reporting of such events. Subsequent development of the Harmful Algal Information System (HAIS) as a global resource is managed by the Intergovernmental Oceanographic Commission (IOC), including HABMAP/ OBIS (https://obis.org/node/33dec23caf65-4fb1-a437-79543c562ef0). Globa lization of the original ICES HAEDAT with records since 1985 for the North Atlantic region, has expanded as the revised ICES-PICES-IOC HAEDAT (https://haedat.iode.org/) and now provides a global template for entry of data on fish-killing and marine mortality events. The IOC torch (not the Olympic one) on the fish-killing theme was carried from the ICES WGHABD and ignited at IOC-IPHAB XI (Paris, 2013) with the establishment of the Task Team on Fish Killing Marine Algae (Resolution XI.7). In subsequent intersessional periods the major tasks were primarily directed towards integrating descriptive data and developing knowledge on ichthyotoxic microalgae and their putative toxins, addressed by participation at conferences, project meetings and workshops to yield reports and primary publications. An international colloquium on the fish-killing algal theme was coordinated by IPHAB and GlobalHAB and co-sponsored by IOC, SCOR and the Fig. 3. Invited speakers and hosts of the Advanced International Colloquium and Technical Workshop on Fish-Killing HABs. Puerto Varas, Chile October 811, 2019. Photo courtesy of Oscar Espinosa, IFOP. HARMFUL ALGAE NEWS NO. 83 / 2026 Harmful Algae News An IOC Newsletter on Toxic Algae and Algal Blooms No. 83 June 2026 https://hab.ioc-unesco.org/ Long and Winding Sea-lanes for Fish-Killing Algal Events An ancient idiom dead fish rot (or stink) from the head down possibly attributable to Turkish or Persian fishers but the orig Fig. 2. Programme for the Advanced International Colloquium and Technical Workshop on fish killing marine algae and their effects. blooms. The WG also decided to revise the classic but outdated Cooperative Research Report [2] on HAB effects on mariculture and marine fisheries published in 1992 for Chilean government, through CORFO and cooperation of CREAN-IFOP (reported in HAN 63 [3]) (Fig. 2). The colloquium convenors invited international experts to Puerto Varas, Chile in 2019 to review disciplinary knowledge on all aspects of fish-killing algae and associated mortality events (Fig. 3). A p ins were added during the IPHAB XVII Intersessional (2025-2026), but the total meagre reported ichthyotoxins score (by March 2025) (zero goniodomins, zero prymnesins, one karlotoxin [sterolysin]) has increased dramatically (by February 2026): seven goniodomins, four prymnesins, one karlotoxin, and m (admittedly controversial) explain how toxigenic blooms may directly kill fish in aquaculture operations [e.g., 11]. Access to comprehensive time-series databases on HAB events (HAEDAT, HAIS/ OBIS) has allowed for interpretation of fish-killing events over decades on a regional geographical basis, e Catastrophic marine mass mortalities, shellfish toxicity and human respiratory problems from a Karenia cristata dinoflagellate bloom in South Australia, 20252026 Fig. 1. Satellite chlorophyll image from March 2024 showing widespread offshore diatom blooms in response to a massive upwelling event du from which the species name cristata is derived), and a longer hypocone with the right lobe slightly longer than the left. Scanning electron microscopy revealed that the crest was formed by a slight elevation of the right side of the apical groove. On the dorsal side, the apical groove extended to o Unprecedented bloom of Fibrocapsa japonica on French coasts Fig. 1. Map of the different bays in southern Brittany monitored as part of the REPHY program. Since 1987, the REPHY (French Phytoplankton and Hydrology Monitoring Network in Coastal Waters), operated by IFREMER, has conducted long-term m Fig. 3. Light microscope images of living Fibrocapsa japonica cells. Scale bars = 20 μm. French waters. REPHY data [9] indicate that the previous maximum abundance occurred in 2013 in the Vilaine estuary, reaching 1.9 x 105 cells L1, approximately 25 times lower than values than maximum concentrati First Record of Fukuyoa sp. (Gambierdiscoideae) in the Northeastern Region of Términos Lagoon, Campeche, Mexico Fig. 1. Map of sampling stations at Términos Lagoon, Campeche, Mexico. The station where Fukuyoa sp. was found is circled in red. Términos Lagoon is a region of substantial economic rele Fig. 2. (AB). Fukuyoa sp. in ventral view. (C). Dorsal view. (D). Antapical view showing plates S. d. p., 1, 1. (EF). Ventral view showing plates 1, 1,2, 7, S. d. p., 1,1. (GH). Antapical view showing plates 1p,2,3, 1, 2. Scale bars = 20 μm. in Australia [6] recorded F. paulensis at temperatures of Trophic interactions shape ciguatera risk in a warming ocean Ciguatera is one of the most widespread marine poisonings worldwide, caused by the consumption of fish that bioaccumulate ciguatoxins (CTXs) produced by dinoflagellate species belonging to the genus Gambierdiscus. Its expansion into non-en drivers such as temperature variability and habitat disturbance. Calibration and validation with empirical data on cell densities, toxin concentrations, and ecosystem dynamics will be essential to generate robust predictions. The inclusion of spatial structure and coupling with human health risk mod Red and green waters in southern B rittany (France) in March 2026 linked to a bloom of Mesodinium spp. Fig. 1. Map of reported water discoloration events in southern Brittany (1012 March 2026) based on PHENOMER observations and direct reports. Locations include the Bay of Audierne and the Bay of C Fig. 3. Sentinel-2 satellite image (11 March 2026) showing the spatial extent of the bloom in southern Finistère, with burgundy-red patches indicative of high Mesodinium surface concentrations. are more stable and impart a green coloration. This transformation can occur within minutes, explaining t Fig. 6. Cells of Mesodinium major. 13. Different views of living cells. 46. Representation of pigment dynamics during Mesodinium cell degradation: transition from phycoerythrin-dominated red coloration to chlorophyll-dominated green coloration following cell lysis. All images to scale. accompanied Who turned on the light? First report of extensive bioluminescent blooms of the heterotrophic dinoflagellate Noctiluca scintillans with low abundance of bioluminescent bacteria in the Gulf of Nicoya, Costa Rica Historically, the Gulf of Nicoya has experienced recurrent algal blooms, including events Fig. 2. Dominant dinoflagellate of the Noctiluca scintillans algal bloom around Cedros Island. (A) Bloom of N. scintillans. (B) Ciliate fed on by Noctiluca, Strombidium sp. (C) Culture of bioluminescent bacteria. (D, E) bioluminescence observed at night on Cedros Island and surrounding areas (photog estuaries supporting fisheries, tourism, and biodiversity. Monitoring these processes allows differentiation between benign and harmful blooms and supports the preservation of ecosystem integrity. Ultimately, such phenomena not only expand scientific understanding but also underscore the resilience International Conference on Molluscan Shellfish Safety (ICMSS) Dear colleagues, We wanted to draw your attention to the upcoming International Conference on Molluscan Shellfish Safety (ICMSS), taking place 611 September 2026 at the University of Exeter, UK. Further details, including registration (w DART in action: Scientists launch regional effort against toxic diatoms Scientists from across Asia have come together to tackle the growing threat of toxic diatoms that produce neurotoxin Domoic Acid (DA). On 1718 March 2026, researchers from China, Malaysia, and Singapore gathered in Qingdao, Chin Fig. 2. Kick-off meeting and research presentations. (A) Nancheng Chen, the lead PI, delivers the opening address. (BD) PIs from participating countries presenting their national research plans. (EF) Selected presentations delivered during the workshop. molecular tools can greatly improve our abilit IOC-FAO Intergovernmental Panel on Harmful Algal Blooms (IPHAB) Extraordinary online Session 27 October 2026 and 18th Session (IPHAB-XVIII), 1820 March 2027, FAO, Rome The Intergovernmental Panel on Harmful Algal Blooms (IPHAB) was established in 1992 to strengthen the scientific, managerial, and fi