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 during the year preceding the 2025 Karenia bloom, which occurred mainly within Spencer Gulf and Gulf St Vincent, South Australia. https://oceancurrent. aodn.org.au. In early March 2025, surfers off the Fleurieu Peninsula, near Adelaide (South Australia), began suffering respiratory irritation, which they linked to a yellowgreen algal bloom (Fig. 1), accompanied by a thick sea foam and dead marine life washing up onshore (Fig. 2). The bloom subsequently expanded to Yorke Peninsula, Kangaroo Island, Gulf St Vincent, and parts of the Spencer Gulf. As of May 2026, 15 months later, Karenia species are still present at abundances of ~104 cells L-1 in some coastal areas of South Australia, although both abundances and distribution have markedly declined from their peak in mid-to-late 2025. Surfers, beachgoers and coastal residents reported illnesses ranging from skin and eye irritation to respiratory symptoms such as coughing and shortness of breath. Public health advisories recommended avoiding affected waters and bloom-generated foams and seeking medical attention if symptoms develop. Testing of commercially harvested oysters, mussels, cockles and scallops detected brevetoxins in shellfish, resulting in the closure of some South Australian oyster harvesting areas for approximately eight months during 2025. Satellite images of the chlorophyll-a anomalies over the past 20 years, covering the period from May to September 2025 [5] showed that the anomalously high chlorophyll region covered an 6 estimated 20,000 km2. Mass mortalities affected at least 770 marine fish, mammals, birds and invertebrates, also disrupting commercial fisheries (calamari), aquaculture (abalone) and tourism industries (https://www. inaturalist.org/projects/sa-marinemortality-events-2025-2026). Previously known marine HAB-forming taxa in the region [1] included species causing water discolorations (Noctiluca), those responsible for fish kills (Heterosigma akashiwo, Chattonella marina, Karenia mikimotoi), producing seafood toxins (Alexandrium minutum, A. pacificum). However, such a prolonged marine mass mortality event affecting fish, mammals, birds and invertebrates, combined with associated human health impacts, had never previously been documented in Australia. Water testing in March 2025 revealed the co-occurrence of several Karenia species, including Karenia mikimotoi [2]. Blooms of this species had previously been recorded in the region in March 1995 and FebruaryMarch 2014 [34], during which massive fishkill events occurred. In May 2025, brevetoxins were confirmed for the first time in Australian waters, suggesting the presence of a brevetoxin-producing Karenia species. A massive six-month effort by 24 scientists [5] from 10 organisations in Australia, New Zealand, and the U.K., led by Professor Shauna Murray, involved culturing, light and scanning electron microscopy, molecular techniques, and toxin chemistry analyses (partly funded by the Fisheries Research and Development Corporation, FRDC). This work ultimately identified and confirmed K. cristata as the toxinproducing species, with a brevetoxin profile (BTX-2, BTX-3, BTX-B5), that differs from the well-studied K. brevis, as it does not produce BTX-1 (Type A) analogues. The dinoflagellate K. cristata (Fig. 3) had previously only been reported from two cold-water locations: False Bay and Walker Bay, South Africa [6], in the mid-1990s, and a remote island off the coast of Newfoundland (French Territory) [7]. The pale yellow-green cells (2132μm long, 1629 μm wide) were fragile, fast swimming, dorsoventrally compressed (914 μm deep), and consisted of a short hemispherical epicone with a minute apical crest (cr; Fig. 2. Seafoam and dead fish on Adelaide beaches, MayOctober 2025. Photos: Samantha Sea; Shauna Murray. 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