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 monitoring of phytoplankton species along the French coastline. Coupled since 2013 with the citizen science program Phenomer (https://www.phenomer.org/) [1], which aims to collect public reports of discoloured water events along the French coasts, these initiatives provide substantial spatial coverage and a high level of information for the study of blooms. Between November 2025 and January 2026, samples collected as part of the REPHY monitoring program, together with reports of brown-coloured waters exhibiting visible mucilaginous aggregates, enabled IFREMER to detect a bloom of the raphidophyte Fibrocapsa japonica in southern Brittany (Fig 1). The observation of a bloom of such magnitude is unprecedented along the French coasts since the establishment of the REPHY monitoring program. Twice a month, vertical profiles of various physicochemical parameters (temperature, salinity, dissolved oxygen, fluorescence and turbidity) were collected throughout the entire water column at REPHY sampling stations. During routine samplings conducted at the Men er Roué station in Quiberon Bay and the Concarneau large station in Concarneau Bay (Fig. 1) on November 18, 2025, unusually high fluorescence peaks were recorded. Measurements recorded in Quiberon Bay on November 18, 2025 (Fig. 2) indicated a homogeneous water column in terms of both salinity and temperature, with values around 33 and 14 C, respec8 northward up to the bay of Brest (Fig. 4). The northward displacement is most likely attributable to the persistent southerly winds in the area during this period. The geomorphology of Brittany, characterised by a succession of semi-enclosed bays and substantial riverine nutrient inputs, likely further supported bloom development. An unusually high abundance of Karenia spp. (mostly Karenia mikimotoi) was also recorded during the same period, reaching 3.3 x 104 cells L1 in Quiberon Bay on November 18, 2025. Both Fibrocapsa and Karenia are classified by the French sanitary agency Anses as potential producers of brevetoxins (BTXs) [2], phycotoxins known to pose risks to shellfish consumers [3] and with toxic effects in marine fauna, including fish kills [4]. Chemical analyses, using an LCMS/MS method developed within the EMERGTOX monitoring program for emerging marine toxins in shellfish [5], were therefore conducted on eight shellfish samples (pools of several individuals of blue mussels, Mytilus spp., and Pacific oysters, Magallana gigas, separately) collected in Quiberon Bay and Morbihan Gulf. All thirteen targeted brevetoxins were below detection levels [6]. Additional screening for other Karenia-associated toxin families (tamulamides, brevisulcatic acids, gymnocins, brevisulcenals, brevisamide, brevenal, brevesin, and several brevetoxins not covered by the EMERGTOX method) also yielded negative results. Fibrocapsa japonica, described in Japan in 1973 by Toriumi and Takano [7], was first reported along the French coasts in 1991 [8]. It has since been regularly observed, but this represents the first bloom of such magnitude in tively, consistent with seasonal conditions. In contrast, unusually high fluorescence values were recorded in the upper few meters of the water column (04 m), reaching up to 35 FFU, indicating elevated chlorophyll-a concentration. This was confirmed by very high chlorophyll-a concentration measured in the subsurface sample (105.7 μg L1). These values decreased from 4 m depth to the seabed (10 m), reflecting the presence of a surface bloom. This was consistent with elevated dissolved oxygen concentrations at the surface (~10.8 mg L1 at 1 m), which decreased along with fluorescence, indicating intense photosynthetic activity in surface waters. Turbidity values exhibited a similar pattern, suggesting a high load of suspended organic matter. Light microscopy observations using the Utermöhl method revealed a bloom of Fibrocapsa japonica (Fig. 3) and molecular identification based on culture sequencing of D1-D3 region of the LSU rDNA gene, using D1r/D3b primers, confirmed the species. A bloom maximum was recorded in Quiberon Bay on 18 November 2025, reaching 4.8 x 106 cells L1. REPHY monitoring further showed that the bloom persisted over a ten-week period and p ro g re s s ive - Fig. 2. Vertical profile of physicochemical parameters recorded in Quiberon Bay ly migrated on 18 November, 2025. 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