POSTER SESSION 2
10:30–12:30, Tuesday, September 15
Poster Session | 1 | 2 | 3 | 4 | Schedule at a Glance
ABSTRACT 1276 | POSTER 62
DETECTING ANOMALOUS BLOOM DYNAMICS FROM SENTINEL-3 CHLOROPHYLL-A TIME SERIES: THE 2021 EMERGENCE OF LINGULAULAX POLYEDRA RED TIDES IN SOUTHERN BRITTANY (FRANCE)
Phytoplankton blooms in coastal ecosystems arise from complex interactions between environmental forcing and community structure, occasionally leading to intense high-biomass events such as red tides. In southern Brittany, an unprecedented bloom of Lingulaulax polyedra occurred in summer 2021, raising the question of whether this event represented an anomaly or the emergence of a new bloom regime. We used daily satellite observations (Sentinel-3/OLCI) to investigate interannual variability in bloom dynamics over the period 2016 – 2025. Chlorophyll-a (Chl-a) was retrieved from remote-sensing reflectance using a band-switching bio-optical algorithm optimized for high-biomass conditions. On every image that was at least 20% cloud-free, pixels with Chl-a ≥ 30 mg·m–3 were considered as signatures of high-biomass coastal blooms. The mean number of bloom pixels increased markedly after the exceptional 2021 year. To identify distinct bloom seasonality patterns, hierarchical clustering was applied to annual seasonal cycles in the number of bloom pixels, using 3-day-averaged time series. The clustering analysis identified 2021 as a distinct year – characterized by a unique seasonal structure and the highest number of bloom pixels – but did not separate years before and after 2021, indicating no irreversible change in bloom seasonality. Phytoplankton data from a regular monitoring survey and from a citizen science program independently confirmed the increase in bloom events from 2021 to 2024, and the higher prevalence of dinoflagellates in the community. These results show how high-frequency satellite remote sensing can document changes in bloom dynamics in coastal systems and inform decisions regarding ecosystem management.
Amalia Maria Detoni, Institut des Substances et Organismes de la Mer (ISOMER – Nantes Université), [email protected], https://orcid.org/0000-0002-7893-5370
Maria Laura Zoffoli, Consiglio Nazionale delle Ricerche, Istituto di Scienze Marine (CNR-ISMAR), Trieste, Italy, [email protected], https://orcid.org/0000-0003-1892-0051
Victor Pochic, Nantes Université, Institut des Substances et Organismes de la Mer, ISOMER, [email protected], https://orcid.org/0000-0002-0885-0312
Pierre Gernez, Nantes Université, Institut des Substances et Organismes de la Mer, ISOMER, [email protected], https://orcid.org/0000-0003-2055-410X
Poster Session | 1 | 2 | 3 | 4 | Schedule at a Glance
